S1P (sphingosine 1-phosphate) represents one of the key latest additions to the list of vasoactive substances that modulate vascular tone. PAR-2 (proteinase activated receptor-2) has been shown to be involved in cardiovascular function. In the present study, we investigated the involvement of PAR-2 in S1P-induced effect on vascular tone. The present study has been performed by using isolated mouse aortas. Both S1P and PAR-2 agonists induced endothelium-dependent vasorelaxation. L -NAME ( N G -nitro- L -arginine methyl ester) and wortmannin abrogated the S1P-induced vasorelaxatioin, while significantly inhibiting the PAR-2-mediated effect. Either ENMD1068, a PAR-2 antagonist, or gabexate, a serine protease inhibitor, significantly inhibited S1P-induced vasorelaxation. Aortic tissues harvested from mice overexpressing PAR-2 displayed a significant increase in vascular response to S1P as opposed to PAR-2-null mice. Immunoprecipitation and immunofluorescence studies demonstrated that S1P 1 interacted with PAR-2 and co-localized with PAR-2 on the vascular endothelial surface. Furthermore, S1P administration to vascular tissues triggered PAR-2 mobilization from the plasma membrane to the perinuclear area; S1P-induced translocation of PAR-2 was abrogated when aortic rings were pre-treated with ENMD1068 or when caveolae dysfunction occurred. Similarly, experiments performed in cultured endothelial cells (human umbilical vein endothelial cells) showed a co-localization of S1P 1 and PAR2, as well as the ability of S1P to induce PAR-2 trafficking. Our results suggest that S1P induces endothelium-dependent vasorelaxation mainly through S1P 1 and involves PAR-2 transactivation.

Sex differences in Ca 2+ -dependent signalling and homoeostasis in the vasculature of hypertensive rats are well characterized. However, sex-related differences in SOCE (store-operated Ca 2+ entry) have been minimally investigated. We hypothesized that vascular protection in females, compared with males, reflects decreased Ca 2+ mobilization due to diminished activation of Orai1/STIM1 (stromal interaction molecule 1). In addition, we investigated whether ovariectomy in females affects the activation of the Orai1/STIM1 pathway. Endothelium-denuded aortic rings from male and female SHRSP (stroke-prone spontaneously hypertensive rats) and WKY (Wistar–Kyoto) rats and from OVX (ovariectomized) or sham female SHRSP and WKY rats were used to functionally evaluate Ca 2+ influx-induced contractions. Compared with females, aorta from male SHRSP displayed: (i) increased contraction during the Ca 2+ -loading period; (ii) similar transient contraction during Ca 2+ release from the intracellular stores; (iii) increased activation of STIM1 and Orai1, as shown by the blockade of STIM1 and Orai1 with neutralizing antibodies, which reversed the sex differences in contraction during the Ca 2+ -loading period; and (iv) increased expression of STIM1 and Orai1. Additionally, we found that aortas from OVX-SHRSP showed increased contraction during the Ca 2+ -loading period and increased Orai1 expression, but no changes in the SR (sarcoplasmic reticulum)-buffering capacity or STIM1 expression. These findings suggest that augmented activation of STIM1/Orai1 in aortas from male SHRSP represents a mechanism that contributes to sex-related impaired control of intracellular Ca 2+ levels. Furthermore, female sex hormones may negatively modulate the STIM/Orai1 pathway, contributing to vascular protection observed in female rats.

AngII (angiotensin II) induces atherosclerosis and AAAs (abdominal aortic aneurysms) through multiple proposed mechanisms, including chemotaxis. Therefore, we determined the effects of whole-body deficiency of the chemokine receptor CCR2 (CC chemokine receptor 2) on these diseases. To meet this objective, apoE (apolipoprotein E) −/− mice that were either CCR2 +/+ or CCR2 −/− , were infused with either saline or AngII (1000 ng·kg −1 of body weight·min −1 ) for 28 days via mini-osmotic pumps. Deficiency of CCR2 markedly attenuated both atherosclerosis and AAAs, unrelated to systolic blood pressure or plasma cholesterol concentrations. During the course of the present study, we also observed that AngII infusion led to large dilatations that were restricted to the ascending aortic region of apoE −/− mice. The aortic media in most of the dilated area was thickened. In regions of medial thickening, distinct elastin layers were discernable. There was an expansion of the distance between elastin layers in a gradient from the intimal to the adventitial aspect of the media. This pathology differed in a circumscribed area of the anterior region of ascending aortas in which elastin breaks were focal and almost transmural. All regions of the ascending aorta of AngII-infused mice had diffuse medial macrophage accumulation. Deficiency of CCR2 greatly attenuated the AngII-induced lumen dilatation in the ascending aorta. This new model of ascending aortic aneurysms has pathology that differs markedly from AngII-induced atherosclerosis or AAAs, but all vascular pathologies were attenuated by CCR2 deficiency.

The present study investigated the role of ROS (reactive oxygen species) and COX (cyclo-oxygenase) in ethanol-induced contraction and elevation of [Ca 2+ ] i (intracellular [Ca 2+ ]). Vascular reactivity experiments, using standard muscle bath procedures, showed that ethanol (1–800 mmol/l) induced contraction in endothelium-intact (EC 50 : 306±34 mmol/l) and endothelium -denuded (EC 50 : 180±40 mmol/l) rat aortic rings. Endothelial removal enhanced ethanol-induced contraction. Preincubation of intact rings with L -NAME [ N G -nitro- L -arginine methyl ester; non-selective NOS (NO synthase) inhibitor, 100μmol/l], 7-nitroindazole [selective nNOS (neuronal NOS) inhibitor, 100μmol/l], oxyhaemoglobin (NO scavenger, 10μmol/l) and ODQ (selective inhibitor of guanylate cyclase enzyme, 1μmol/l) increased ethanol-induced contraction. Tiron [O 2 − (superoxide anion) scavenger, 1 mmol/l] and catalase (H 2 O 2 scavenger, 300 units/ml) reduced ethanol-induced contraction to a similar extent in both endothelium-intact and denuded rings. Similarly, indomethacin (non-selective COX inhibitor, 10μmol/l), SC560 (selective COX-1 inhibitor, 1μmol/l), AH6809 [PGF 2α (prostaglandin F 2α )] receptor antagonist, 10μmol/l] or SQ29584 [PGH 2 (prostaglandin H 2 )/TXA 2 (thromboxane A 2 ) receptor antagonist, 3μmol/l] inhibited ethanol-induced contraction in aortic rings with and without intact endothelium. In cultured aortic VSMCs (vascular smooth muscle cells), ethanol stimulated generation of O 2 − and H 2 O 2 . Ethanol induced a transient increase in [Ca 2+ ] i , which was significantly inhibited in VSMCs pre-exposed to tiron or indomethacin. Our data suggest that ethanol induces vasoconstriction via redox-sensitive and COX-dependent pathways, probably through direct effects on ROS production and Ca 2+ signalling. These findings identify putative molecular mechanisms whereby ethanol, at high concentrations, influences vascular reactivity. Whether similar phenomena occur in vivo at lower concentrations of ethanol remains unclear.

The metabolic syndrome, Type II (non-insulin-dependent) diabetes and obesity are associated with endothelial dysfunction and increased plasma concentrations of NEFAs (non-esterified fatty acids; free fatty acids). The present study was undertaken to define the inhibitory effects of saturated NEFAs on EDR (endothelium-dependent relaxation). Experiments were performed in rings of rabbit aorta to establish (i) dose–response relationships, (ii) the effect of chain length, (iii) the effect of the presence of double bonds, (iv) reversibility and time course of inhibition, and (v) the effect on nitric oxide production. Aortic rings were incubated (1 h) with NEFA–albumin complexes derived from lauric (C 12:0 ), myristic (C 14:0 ), palmitic (C 16:0 ), stearic (C 18:0 ) and linolenic (C 18:3 ) acids. EDR induced by acetylcholine (0.1–10 μmol/l) was measured after pre-contraction with noradrenaline. Inhibition of EDR was dose-dependent (0.5–2 mmol/l NEFA), and the greatest inhibition (51%) was observed with stearic acid (2 mmol/l). Lauric acid had the smallest inhibitory effect. The inhibitory effects were always reversible and were evident after 15 min of incubation. Linolenic acid caused a significantly lower inhibition of EDR than stearic acid. SOD (superoxide dismutase) restored the inhibitory effect caused by NEFAs, suggesting the involvement of ROS (reactive oxygen species) in removing nitric oxide. The nitric oxide concentration measured after exposure of the rings to acetylcholine was lower after incubation with NEFAs than with Krebs buffer alone. This finding is consistent with removal of nitric oxide by ROS. This claim was supported by the demonstration of increased concentrations of nitrated tyrosine in the rings incubated with NEFAs.

Systemic arterial compliance has been known to increase during healthy pregnancy, whereas, recently, the carotid artery has been reported to stiffen. To clarify this controversy, we simultaneously measured aortic PWV (pulse wave velocity) and carotid artery elastic parameters in a cohort of pregnant women. Twelve normotensive pregnant women were studied longitudinally during the three trimesters of pregnancy (T 1 , T 2 and T 3 respectively) and 12 weeks PP (postpartum). Carotid artery diastolic diameter and pulsatile distension was measured by an echo-wall tracking method and carotid pulse pressure by applanation tonometry. Carotid strain, compliance, distensibility coefficient, stiffness index β, E inc (incremental elastic modulus) and augmentation index were calculated. Aortic PWV was determined to estimate aortic distensibility. All carotid artery elastic parameters indicated significant stiffening from T 1 to T 3 (1.8±0.2 versus 2.9±0.3 mmHg for E inc ), which was reversed after delivery (2.3±0.2 mmHg). Aortic PWV decreased during pregnancy (6.2±0.2 versus 5.4±0.2 m/s) and increased in the PP period (6.7±0.2 m/s). No correlation was found between changes in carotid artery elastic parameters and changes in aortic PWV either from T 1 to T 3 or from T 3 to PP. The carotid artery exhibits regionally specific stiffening during pregnancy, which appears to represent a qualitatively different change in arterial elastic behaviour.

Transfer function techniques are increasingly used for non-invasive estimation of central aortic waveform characteristics. Non-invasive radial waveforms must be calibrated for this purpose. Most validation studies have used invasive pressures for calibration, with little data on the impact of non-invasive calibration on transfer-function-derived aortic waveform characteristics. In the present study, simultaneous invasive central aortic (Millar Mikro-tip® catheter transducer) and non-invasive radial (Millar® Mikro-tip® tonometer) pressure waveforms and non-invasive brachial pressures (Dinamap®) were measured in 42 subjects. In this cohort, radial waveforms were calibrated to both invasive and non-invasive mean and diastolic pressures. From each of these, central waveforms were reconstructed using a generalized transfer function obtained by us from a previous cohort [Hope, Tay, Meredith and Cameron (2002) Am. J. Physiol. Heart Circ. Physiol. 283 , H1150–H1156]. Waveforms were analysed for parameters of potential clinical interest. For calibrated radial and reconstructed central waveforms, different methods of calibration were associated with differences in pressure ( P <0.001), but not time parameters or augmentation index. Whereas invasive calibration resulted in little error in transfer function estimation of central systolic pressure (difference −1±8 mmHg; P =not significant), non-invasive calibration resulted in significant underestimation (7±12 mmHg; P <0.001). Errors in estimated aortic parameters differed with non-invasively calibrated untransformed radial and transfer-function-derived aortic waveforms (all P <0.01), with smaller absolute errors with untransformed radial waveforms for most pressure parameters [systolic pressure, 5±16 and 7±12 mmHg; pulse pressure, 0±16 and 4±12 mmHg (radial and derived aortic respectively)]. When only non-invasive pressures are accessible, analysis of untransformed radial waveforms apparently produces smaller errors in the estimation of central aortic systolic pressure, and other waveform parameters, than using a generalized transfer function.

This study investigated vascular reactivity in response to acetylcholine, in the presence of acute inhibition of nitric oxide synthase, in the carotid artery and aorta of obese C57Bl6/J mice fed on a high-fat diet for 30 weeks, and of control mice. A subgroup of obese animals was also treated with the ET A receptor antagonist darusentan (50mg·kg -1 ·day -1 ). In vascular rings from control animals, acetylcholine caused endothelium-dependent contractions in the carotid artery, but not in the aorta. In vascular rings from obese mice, contractility to acetylcholine was also evident in the aorta, and that in the carotid artery was increased compared with control mice. ET A receptor blockade by darusentan treatment of the obese mice prevented enhanced vasoconstriction to acetylcholine, resulting in mild vasodilatation. Thus obesity increases endothelium-dependent vasoconstriction in the absence of endothelial nitric oxide. This effect can be completely prevented by chronic ET A receptor blockade, suggesting that endothelin modulates increased endothelium-dependent vasoconstriction in obesity.

Hypertension is a major risk factor in the development of cardiovascular disease. Adenovirus gene transfer of endothelin-1 (Ad.CMV.ET-1) in rats produced significant (5-fold) increases in plasma ET-1 and systemic blood pressure (46%) 4 days after viral administration, compared with β-galactosidase (Ad.CMV.β-gal) injected as control. The density ( B max ) of the ET receptor ET A measured in aortas was reduced significantly by more than 50% to 17±2fmol·mg -1 of protein for the Ad.CMV.ET-1 group compared with 39±6fmol·mg -1 of protein for the control. There was no change in the density of the smaller population of the ET B sub-type. In agreement, the ratio of ET A mRNA to cyclophilin mRNA (a housekeeping gene) measured by Northern analysis was reduced in Ad.CMV.ET-1 rats compared with controls. The ratio of mRNA encoding the ET B sub-type did not change. ET-1 vasoconstriction was significantly reduced ( P <0.05) in aortas from Ad.CMV.ET-1-treated rats [pD 2 = 8.67±0.14 (where pD 2 is -log 10 EC 50 ); n = 11] versus the control (pD 2 = 9.11±0.06; n = 14) but there was no significant difference in the potency of two other vasoconstrictors tested (noradrenaline and Arg-vasopressin), indicating this was a specific effect on ET receptors. There was no change in the affinity of ET-1 binding to either receptor sub-type in the experimental group compared with the control, demonstrating that the attenuation in the constrictor response is the result of the reduced density of receptors rather than a change in affinity. The results show that ET A (but not ET B ) receptors are modulated in this experimental model of hypertension and provide further evidence for selective blockade of the ET A receptor as a therapeutic strategy.

Aging impairs endothelial function and the vascular tone regulation, although the precise mechanism remains unclear. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by vascular endothelial cells. Because ET-1 has a potent vasoconstrictor effect on vessels, it may be involved in the regulation of vascular tonus. We hypothesized that aging causes a decrease in ET-1 expression in aorta, and that exercise training improves the aging-induced decrease in ET-1 expression in aorta. This study was performed to examine whether gene expression of ET-1 in the aorta of rats is altered by aging and subsequent exercise training. We studied expression of ET-1 mRNA in the aortas of sedentary young rats (Sedentary young group, 4 months old), sedentary aged rats (Sedentary aged group, 23 months old), and swim trained aged rats (Training aged group, 23 months old; swimming training for 8 weeks, 5days/week, 90min/day). The expression of ET-1 mRNA in the aorta was analysed by real-time quantitative PCR. Body weight and resting heart rate were significantly lower in the Training aged group compared with the Sedentary aged group. These results suggest that the Training aged rats exhibited physiological effects from exercise training. The expression of ET-1 mRNA in the aorta was markedly lower in Sedentary aged group compared with the Sedentary young group, whereas it was significantly higher in Training aged group compared with the Sedentary aged group. These results show that the expression of ET-1 mRNA in the aorta is decreased by aging, and that the expression is increased by exercise training. Therefore, the present study provides a possibility that exercise training improves endothelial function through up-regulation of the aging-induced decrease in ET-1 expression in the aorta.

Mean arterial pressure (MAP) is estimated at the brachial artery level by adding a fraction of pulse pressure (form factor; = 0.33) to diastolic pressure. We tested the hypothesis that a fixed form factor can also be used at the aortic root level. We recorded systolic aortic pressure (SAP) and diastolic aortic pressure (DAP), and we calculated aortic pulse pressure (PP) and the time-averaged MAP in the aorta of resting adults ( n = 73; age 43±14 years). Wave reflection was quantified using the augmentation index. The aortic form factor (range 0.35-0.53) decreased with age, MAP, PP and augmentation index (each P <0.001). The mean form factor value (0.45) gave a reasonable estimation of MAP (MAP = DAP+0.45PP; bias = 0±2mmHg), and the bias increased with MAP ( P <0.001). An alternative formula (MAP = DAP+PP/3+5mmHg) gave a more precise estimation (bias = 0±1mmHg), and the bias was not related to MAP. This latter formula was consistent with the previously reported mean pulse wave amplification of 15mmHg, and with unchanged MAP and diastolic pressure from aorta to periphery. Multiple linear regression showed that 99% of the variability of MAP was explained by the combined influence of DAP and SAP, thus confirming major pressure redundancy. Results were obtained irrespective of whether the marked differences in heart period and extent of wave reflection between subjects were taken into account. In conclusion, the aortic form factor was strongly influenced by age, aortic pressure and wave reflection. An empirical formula (MAP = DAP+PP/3+5mmHg) that is consistent with mechanical principles in the arterial system gave a more precise estimate of MAP in the aorta of resting humans. Only two distinct pressure-powered functions were carried out in the (SAP, DAP, MAP, PP) four-pressure set.

Ultrasound examinations of the heart and major peripheral arteries have been performed as separate procedures; both potentially limited by suboptimal views in certain subjects and the inability to obtain ideal pictures of particular intracardiac structures. Transvenous ultrasound may offer new advantages in certain areas, we therefore studied six adult baboons using a single-plane 5.5–10 MHz transducer mounted on a 10 French (10F) catheter, introduced via the right femoral vein and positioned under fluoroscopic control. Imaging and Doppler studies were performed to delineate cardiovascular anatomy as well as ventricular function response to positive (dobutamine) and negative inotropic (esmolol) agents. The procedure was safe and feasible in all cases. Clear and novel two-dimensional and flow information were obtained from the iliac arteries, descending aorta, both renal artery origins, ascending aorta, including the aortic arch, main pulmonary artery and its bifurcation, as well as head and neck vessels. Novel intracardiac views were obtained, including right ventricular long axis, left ventricular apex and ‘flask’ views of the left ventricle. Excellent dynamic information for left ventricular function was also available [e.g. myocardial V max of the anterior left ventricular wall was 6.8±2.5 cm/s at rest, 14.6±5.5 cm/s after dobutamine ( P = 0.009) and 4.5±1 cm/s after esmolol ( P = 0.03 compared with control)]. We conclude that, in adult primates, transvenous ultrasound safely and reliably provides novel information of cardiovascular structure and function.

We have examined the effects of pre-hepatic portal hypertension on the responsiveness of aorta from Wistar and Sprague–Dawley rats. Rats were made portal hypertensive by creating a calibrated portal vein stenosis, or sham operated. In rat aorta, there was no significant difference between portal hypertensive and sham-operated animals in the contractile potency of KCl, noradrenaline or phenylephrine. In aortas from Wistar rats, the maximum response to KCl (0.71±0.12 ;g) and noradrenaline (1.00±0.17 ;g) but not phenylephrine (0.86±0.10 ;g) in portal hypertensive animals was significantly increased compared with that in sham-operated animals (0.45±0.04 ;g, 0.57±0.07 ;g, 0.71±0.05 ;g respectively). In aortas from Sprague–Dawley rats, the maximum response to KCl (1.21±0.21 ;g) and phenylephrine (1.54±0.30 ;g) but not noradrenaline (0.93±0.09 ;g) in portal hypertensive animals was significantly increased compared with that in sham-operated animals (0.59±0.09 ;g, 0.76±0.11 ;g, 1.04±0.10 ;g respectively). There was no difference between portal hypertensive and sham-operated Wistar rats in the affinity or maximum number of binding sites for [ 3 H]prazosin to α 1 -adrenoceptors in cardiac ventricular membranes. It is concluded that portal hypertension tends to produce an increase rather than a decrease in the contractile response to vasoconstrictors in aorta from both Wistar and Sprague–Dawley rats. This suggests that the diminished responsiveness to vasoconstrictors reported in portal hypertensive rats in vivo is not due to a diminished responsiveness at the level of the vascular smooth muscle.

1. Patients with an elevated plasma level of either homocysteine or cholesterol are at increased risk of cardiovascular disease. Both methionine, the precursor of homocysteine, and cholesterol are found primarily in the same foods; therefore we investigated the effect of methionine feeding alone, cholesterol feeding alone, and both, on the thickness of the aortic wall and the aortic elastic lamina of normotensive animals. 2. Twenty normotensive rats were divided into four groups of five animals. The following diet was administered for 15 weeks: normal chow; normal chow supplemented with 2% methionine; normal chow supplemented with 2% cholesterol; normal chow supplemented with 2% methionine+2% cholesterol. 3. The results showed a 3-fold decrease ( P < 0.003) in the aortic elastic lamina in the 2% methionine group and a 2.5-fold decrease in the 2% cholesterol group compared with the normal chow group. There was a 9-fold ( P < 0.0003) decrease in the 2% methionine+2% cholesterol group compared with the normal chow group. Furthermore, feeding with methionine plus cholesterol significantly increased aortic wall thickness compared with the methionine group, cholesterol group or control. 4. These results demonstrate an augmented effect of cholesterol plus methionine in the deterioration of the aortic elastic lamina, and furthermore, the combination of these two agents increases the thickness of the aortic wall. The results indicate a more important role for these two agents in combination than for either agent alone.

1. The role of nitric oxide as mediator of the vascular alterations present in different models of experimental liver cirrhosis is controversial. In the present study, we evaluated the role of nitric oxide and that of the endothelium in the response to phenylephrine and acetylcholine of isolated aortic rings from chronic bile duct-ligated (29 days) rats and their corresponding controls. Experiments were performed in rings with or without endothelium, in rings pretreated with N -ω-nitro-l-arginine methyl ester (10 −4 mol/l) to inhibit nitric oxide synthesis and in rings pretreated with aminoguanidine (10 −4 mol/l) to inhibit inducible nitric oxide synthesis. 2. Under basal conditions, the maximum absolute tension developed in response to cumulative addition of phenylephrine was significantly decreased in rings from bile duct-ligated animals (1.62 ± 0.06 g) compared with the control rings (2.15 ± 0.099). This hyporesponsiveness to phenylephrine of rings from bile duct-ligated animals was corrected after treatment with N -ω-nitro-l-arginine methyl ester and reduced, but not completely eliminated, in rings without endothelium. In contrast, aminoguanidine did not modify the lower response to phenylephrine rings from bile duct-ligated animals. ED 50 values were not different between groups under any experimental conditions. 3. The endothelium-dependent vasodilatation to acetylcholine in phenylephrine-constricted rings was similar in both groups of animals, control and bile duct ligated, under all experimental conditions. N -ω-nitro-l-arginine methyl ester pretreatment and removal of the endothelium completely abolished the response to acetylcholine in cirrhotic and control rings. 4. These results demonstrate that in aortic rings from cirrhotic, bile duct-ligated rats, increased production of nitric oxide, mainly of endothelial origin, is responsible for the lower contractile response to phenylephrine. Our data, however, do not support the involvement of the inducible nitric oxide synthase isoform in this alteration. In contrast, endothelial vasodilatory response to acetylcholine is not altered in this model of cirrhosis, which indicates that not all mechanisms of nitric oxide release are abnormal.

1. The effects of fish oil supplementation on atherosclerosis in different regions of the aorta in rabbits with diet-induced hypercholesterolaemia were studied. Control and experimental rabbits were fed a 1% cholesterol-enriched diet with or without 10% fish oil supplementation (seven in each group), and were killed after 2 weeks of feeding. The ascending, descending and abdominal aortas as well as the pulmonary artery were harvested for analyses of prostanoid production, malondialdehyde, superoxide dismutase activity and cholesterol levels. The tissues from the other seven rabbits of each group were obtained after 6 weeks of feeding for the identification of atherosclerotic lesions by a Sudan IV stain. 2. The cholesterol-fed rabbits had a significantly higher thromboxane B 2 production, a lower 6-keto-prostaglandin 1α /thromboxane B 2 ratio and a higher malondialdehyde level than the other two groups in the ascending and abdominal aortas as well as the pulmonary artery; this finding paralleled the severity of atherosclerotic lesions. These manifestations were most prominent in the ascending aorta. The fish oil-supplemented rabbits had the most beneficial aortic prostanoid production, attenuated lipid peroxidation and significantly suppressed atherosclerosis. 3. These results suggest that a high-cholesterol diet induces more atherosclerotic lesions, especially on the ascending aorta, in rabbits. A fish oil supplement favours prostanoid production and attenuates lipid peroxidation on all four regions of the great arteries, thus suppressing atherosclerosis in diet-induced hypercholesterolaemic rabbits.

1. Atherosclerosis and aneurysm of the abdominal aorta are associated with thinning of the medial connective tissue. We have investigated the presence of the connective-tissue-degrading metalloproteinases in homogenates prepared from atherosclerotic, aneurysmal and control aortic media. 2. Gelatinase activity was much increased in homogenates from atherosclerotic and aneurysmal aorta [10.911.8 and 13.3 ± 3.3 μg of gelatin hydrolysed h −1 (mg of protein) −1 respectively]. This gelatinase activity was highest at the luminal aspect of the aortic media, where the activity increased three-to five-fold after the destruction of α 2 -macroglobulin. Zymograms demonstrated the principal gelatinase in atherosclerotic aorta to have a molecular mass of about 92 kDa, whereas in aneurysmal aorta there was a spectrum of gelatinase activity from 92 to 55 kDa. 3. Collagenase and stromelysin (proteoglycanase) could be detected by immunoblotting in homogenates of aneurysmal aorta, but rarely in atherosclerotic aorta and never in control aorta. Collagenase and stromelysin activities were low, but increased two-to three-fold after the destruction of tissue inhibitor of metalloproteinases. Collagenase and stromelysin activities were highest at the adventitial aspect of aneurysmal media. 4. The secretion of gelatinase by inflammatory cells at the intima of diseased aorta could have a pathological role in establishing atherosclerotic plaques and medial thinning. Secretion of collagenase, gelatinase and stromelysin from the adventitia could accelerate connective tissue degradation in the media of aneurysmal aorta.

1. Rat aortic rings stop producing prostacyclin upon prolonged washing in buffer. This ‘exhaustion’ is caused by inhibition of cyclo-oxygenase, since these rings still convert cyclic endoperoxides but not arachidonic acid into prostacyclin, and most probably is due to high concentrations of peroxides: it can be accelerated by H 2 O 2 or by interrupting the glutathione cycle, while it is delayed by reduced glutathione. 2. Incubation of exhausted rings in human plasma or in a plasma filtrate restores to some extent prostacyclin formation. This filtrate, in particular from uraemic subjects, also inhibits the H 2 O 2 initiated oxidation of guaiacol by ram seminal vesicle microsomes or horseradish peroxidase. 3. The prostacyclin regulating plasma factor has been partially purified and identified as a stable and very polar molecule of mol. wt. 300–400, able to reactivate prostacyclin generation by exhausted rings. We suggest that one or more low mol. wt. plasma components prolong vascular prostacyclin formation by acting as reducing cofactor for cyclo-oxygenase peroxidase. 4. The main physiological role of this plasma activity is probably to protect the vascular prostacyclin forming system from exhaustion during persistent irritation.

1. Relative potencies (ED 50 ), affinities (assessed as dissociation constants) and efficacies (i.e. ability to activate the receptor) of agonists are useful in subclassifying and differentiating α-adrenoceptors. 2. The postsynaptic α-adrenoceptor of rat aorta is of the α 1 -subtype, but may differ from the α 1 -adrenoceptor of rabbit and guinea pig aortae, based on comparison of relative potencies of selected agonists. 3. By evaluating the relative potency of agonists, qualitative and quantitative species differences between α 1 -adrenoceptors in rat and guinea pig are observed in a variety of test systems in vivo and in vitro. 4. By comparing the relative potencies of aromatic hydroxyl-substituted phenethylamines and imidazolines at α 1 -adrenoceptors in guinea pig aorta, differences in the ability of these two classes of α-adrenoceptor agonists to bind to, and subsequently activate, α 1 -adrenoceptors have been observed. 5. Evaluating the relative potencies of agonists, when used in conjunction with other techniques, provides a valuable method for classifying α-adrenoceptors and for studying α-adrenergic mechanisms.

1. Wistar female rats were made hypertensive by applying a silver clip to the left renal artery and removing the right kidney. In aortas, the proliferation fraction of smooth muscle cells, DNA synthesis and wet weight have been correlated with the blood pressure increase subsequent to the operation. 2. A wave of proliferation of smooth muscle cells in the aortic media is triggered immediately after the highest increased rate of blood pressure. When blood pressure stabilizes at high values, the metabolism of nucleic acid within the aortic media resumes its normal level but the arterial changes previously established persist. 3. The sequence of pathological events responsible for these changes could be: increment of blood pressure; increase in wall stress; proliferation of smooth muscle cells; thickening of arterial wall; correction of the wall stress; end of proliferation. 4. The consequence of this early proliferation of aortic smooth muscle cells is not clear but it is probably one of the mechanisms through which high blood pressure is sustained. It can also participate in atherogenesis, being in this way one of the bases of the well-known relationship between hypertension and atherosclerosis.

1. Rats were bilaterally adrenalectomized and treated for periods of up to 32 days with doses of dexamethasone equivalent to physiological and supraphysiological endogenous glucocorticoid secretion. Aortic production of 6-oxoprostaglandin F 1α (6-oxo-PGF 1α ) was measured by radioimmunoassay of the supernatant fluid from rings of aorta incubated in vitro. 2. Up to 32 days after adrenalectomy, neither adrenalectomy nor dexamethasone (2 μg/day and 20 μg/day) influenced aortic 6-oxo-PGF 1α production. 3. High doses of dexamethasone (60 μg/day for 6 days) in the presence or absence of mineralocorticoid (11-deoxycorticosterone, 600 μg/day) had no effect on aortic 6-oxo-PGF 1α production. 4. in contrast to the lack of effect of dexamethasone administered in vivo , incubation of aortic discs for 5 h with dexamethasone (1 μmol/l) in vitro caused inhibition of aortic 6-oxo-PGF 1α production to 23% of control levels. 5. Alteration in endogenous glucocorticoid secretion is unlikely to be involved in the physiological regulation of aortic 6-oxo-PGF 1α , production.

1. The effect of the hypertensive process on vascular sensitivity to serotonin and methysergide was studied. 2. Isometric contractions were recorded from arteries isolated from spontaneously hypertensive (SHR), Kyoto-Wistar normotensive (WKY), deoxycorticosterone acetate (DOCA)-hypertensive and Sprague-Dawley normotensive rats. 3. Arteries from hypertensive rats (except SHR aorta) were more sensitive (lower ED 30 ) to noradrenaline, serotonin and methysergide relative to those from controls. 4. The magnitude of the leftward shift in ED 30 was similar for the three agonists in mesenteric and tail arteries from DOCA rats, whereas the shift in ED 30 for serotonin and methylsergide in aortae exceeded that to noradrenaline. In SHR, the shift in ED 30 for serotonin and methylsergide in tail and mesenteric arteries was greater than that to noradrenaline; SHR aortae did not differ from WKY aortae. 5. Arteries from hypertensive rats (except SHR aorta) developed a greater maximal contraction to methysergide than those from controls; maximal contractions to noradrenaline and serotonin were either less than or similar to those of controls. 6. The agonistic action of methysergide in DOCA rats paralleled the development of high arterial pressure. Low sodium diet abated the high pressure in DOCA rats and reduced vascular sensitivity to all agonists. 7. These observations support the view that in hypertension there is a generalized increase in vasoconstrictor sensitivity. The major finding is that, in two hypertensive models, there is a uniquely greater increase in vascular responsiveness to the agonistic action of methysergide.

1. Renal cortical and medullary tissue and aortic wall were removed from spontaneously hypertensive rats and from age-matched Wistar-Kyoto control animals at ages 30, 60, 90 and 120 days. The tissues were incubated and the release of prostaglandins into the incubation medium was measured. 2. Compared with Wistar-Kyoto control animals, the release of prostaglandin E from renal medullary tissue in spontaneously hypertensive rats was raised at 30 days (pre-hypertensive stage) and 90 days (early hypertensive stage), but decreased later with further establishment of hypertension. No such trend was seen with renal cortical tissue. Tissue release of prostaglandin F tended to be generally high in the spontaneously hypertensive rats compared with that in the control animals, but the difference was not significant. 3. The release of prostaglandin I 2 , as indicated by measurements of 6-keto prostaglandin F 1α , from aortic wall tissue in the spontaneously hypertensive rat during its pre-hypertensive and early hypertensive stages was similar to values obtained in the age-matched control animal. However, aortic wall prostaglandin I 2 release in spontaneously hypertensive rats increased thereafter, and was significantly raised at 90 and 120 days. No similar trend was observed with thromboxan A 2 release. Release of prostaglandin I 2 and thromboxan A 2 from renal tissues in spontaneously hypertensive rats did not differ significantly from that in control animals. 4. It is suggested that indomethacin-induced aggravation of hypertension in the spontaneously hypertensive rat may result from suppression of aortic wall prostaglandin I 2 formation rather than from the suppression of renal prostaglandin E 2 production.

1. Renin-like enzymes have been isolated from aorta, plasma and kidney tissue of the rat. The enzymes have been compared with respect to pH optima, molecular weight and isoelectric points. 2. Two distinct molecular-weight forms were isolated from plasma. The high-molecular-weight enzyme (mol. wt. > 150 000) appeared to be homogeneous with respect to isoelectric point (pI = 5.3), whereas the dominant lower-molecular-weight form (mol. wt. 44 000) demonstrated isoelectric heterogeneity. 3. The renin-like enzyme isolated from aortic tissue has mol. wt. 44 000 and also demonstrated isoelectric heterogeneity (pI = 5.0, 5.3). Plasma renin was significantly reduced after bilateral nephrectomy (30 h); however, the activity and relative proportions of the two aortic enzymes were not significantly altered. 4. Renin, isolated from kidney homogenates, either in the presence or absence of a variety of proteolytic enzyme inhibitors, had a significantly lower molecular weight (38 000) than the plasma enzyme but demonstrated a similar pattern of isoelectric heterogeneity. 5. in contrast with renin extracted from kidney, approximately 30% of the renin released from kidney cortical slices into Krebs-Ringer bicarbonate had mol. wt. 44 000. Only the 38 000 mol. wt. form was detected after storage of this medium and no change in total renin activity was evident. This suggests that the 38 000 mol. wt. form may be a methodological artifact due to the release of other proteolytic enzymes. 6. With homologous substrate, all fractionated enzymes showed a pH optimum between pH 7.0 and 7.5. 7. The present study indicates that the predominant form of renin released from rat kidney into blood has mol. wt. 44 000. The microheterogeneity of the plasma enzyme with respect to isoelectric point is similar to that of kidney renin. One form of renin (mol. wt. 44 000, pI = 5.0) may be common to kidney, plasma and aorta. The second aortic enzyme (pI = 5.3), however, may be of local origin.

1. The effect of sodium intake on angiotensin-converting enzyme activity in subcellular fractions of aorta (homogenate, mitochondria, microsomes and supernatant) was studied in normotensive and spontaneously hypertensive rats. 2. Angiotensin-converting enzyme activity was extremely high in the supernatant fraction in normotensive and spontaneously hypertensive rats. 3. Total converting enzyme activity in spontaneously hypertensive rats was 34% higher than that in normotensive rats. 4. Increased sodium intake resulted in a marked reduction, almost to zero, of converting enzyme activity in each fraction of aorta in normotensive and spontaneously hypertensive rats. 5. Converting enzyme, widely distributed in subcellular fractions of the aorta, may play a possible rôle in the local control of vascular tone. It is likely that sodium intake inhibits production of the enzyme in vascular tissue.

1. Angiotensin-converting enzyme (ACE) activity was threefold greater in isolated cerebral microvessels obtained from rabbit brain than rat brain. 2. ACE activity was distributed throughout the cerebral microvasculature, since differences were not found between preparations enriched in capillaries as compared with those enriched in arterioles and venules. 3. Aortic tissue from rat and rabbit had little ACE activity compared with the microvessels. 4. ACE activity was tightly associated with endothelial cells and was not released by heparin under conditions where lipoprotein lipase was effectively removed.

1. The extent of reversal of baroreceptor resetting after pressure normalization was studied in rats with renal hypertension of up to 6 months duration. The aortas of these rats when compared with those of 2 month hypertensive rats were thicker (44%) and had a larger calibre (29%). 2. The more severe morphological alterations found in the 6 month hypertensive rats did not interfere with the reversibility of the resetting process. The entire range of pressure for baroreceptor activation showed a small downward displacement after 1 h and was functioning at a completely normal pressure 6 h after pressure normalization. 3. The data show that reversal of resetting from hypertension is a very rapid process that is independent of the duration of hypertension and the severity of morphological lesions. Moreover, they indicate that reversal is a permanent phenomenon because it was also observed after 2 days of pressure normalization.

1. The effects of mechanical activation of aortic sympathetic sensory fibres have been studied in conscious dogs. 2. A cannula covered by an inflatable rubber balloon, previously implanted in the descending thoracic aorta, was used to stretch the aortic walls without obstructing blood flow. 3. Aortic stretch significantly increased mean arterial blood pressure and heart rate from control values in the absence of pseudo-affective reactions. 4. This response indicates that positive feedback sympathetic reflexes are operative in the conscious, fully innervated animal.

1. Long-term changes in the function and structure of arteries and veins in response to an elevation in arterial pressure have been studied in the rabbit after partial abdominal aorta constriction. 2. Transient changes occur in the vasculature in association with the rise in arterial pressure. 3. The dominant change seen after arterial pressure elevation has been maintained for 8 months is an increase in arterial wall mass, including an increase in vascular smooth muscle cell number, and in some arteries an increase in internal diameter. 4. It may be inferred from this limited study of elastic and muscular arteries that structural alteration represents the over-riding response of the vasculature to an elevation in intramural pressure.

1. Sodium movement across the porcine aortic arch in vitro is greater from the intimal to the medial surface than in the reverse direction. 2. A short-circuit current can be measured across the aortic arch and the calculated energy is greater than the energy required to support the net outward sodium movement, suggesting the possibility of active transport of other ions. 3. Net sodium movement is not significantly altered by an adverse gradient on the outside (medial side) but is reduced by a gradient in the opposite direction. 4. Sodium retention within the tissue is increased by a gradient on the medial side. 5. The movement of [ 14 C]inulin is greater from the medial to the intimal surface, suggesting greater porosity on the medial side. A slight rise in both total tissue fluid and extracellular fluid occurred when the sodium concentration on the medial side of the preparation was increased. This did not occur with the sodium concentration increased on the intimal side. The changes were only significant statistically for total tissue fluid. 6. The short-circuit current can be enhanced by adrenaline and reduced by a variety of β-adrenoreceptor-blocking agents. 7. It appears that aortic tissue can actively transport sodium and it is suggested that this mechanism could play a part in blood pressure control.