Advanced cirrhosis is associated with reduced platelet function and altered renal function and sodium handling. Arachidonic acid (AA) metabolites contribute to platelet aggregation and to maintain the response to diuretics in advanced cirrhosis. In the present study, we tested the effects of a dietary supplementation for 8 weeks with a triacylglycerol (triglyceride) enriched in AA (ARASCO®; 4 g/day) or oleic acid (OA) on plasma and membrane fatty acid composition, platelet aggregation and renal prostaglandin (PG) metabolism. At baseline, all patients had reduced platelet aggregation. Patients treated with AA showed a significant increase in the percentage of AA in plasma lipids and membrane phospholipids. These changes were associated with an increased platelet aggregation in response to collagen (from 55.83±20.63 to 67.67±14.44%; P <0.05). At baseline, all urinary AA metabolites, including PGE 2 , 6-keto-PGF 1α , 8-epi-PGF 2α and 11-dehydro-thromboxane B 2 , were elevated in cirrhotic patients when compared with a group of normal subjects. After furosemide treatment, urinary excretion of 11-dehydro-thromboxane B 2 increased significantly. Supplementation with AA did not result in any significant change in urinary PG excretion either before or after diuretic administration. The results of the present study show that dietary supplementation with AA effectively increases the levels of this fatty acid in plasma and membrane phospholipids and improves platelet aggregation. These data suggest a possible novel approach to the treatment of the haemostatic defect observed in these patients.

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.

Endothelin (ET)-1 and thromboxane (Tx) levels are increased in human atherosclerosis. One of the aims of this study was to understand how receptors for a peptide mediator (ET-1) with a long physiological half life, would differ from a lipid mediator (TxA 2 ), with a short physiological half life, in human coronary artery disease (CAD). Secondly, to determine if receptor protein is present in human coronary artery vascular smooth muscle for the recently adopted peptide orphan receptors for urotensin-II, apelin and ghrelin. The ET A receptor subtype predominated in the medial smooth muscle layer of both non-diseased coronary artery (NCA) and CAD. However, this subtype was present at relatively low density in the proliferated intimal layer of CAD. The ET B receptor protein was not altered with CAD, compared with NCA. Tx receptor density was significantly ( P <0.05) increased in both the media and intima of CAD, compared with NCA. There was no alteration in receptor density, on the medial smooth muscle for urotensin-II and apelin with CAD. Interestingly, receptor density for the novel vasodilator peptide ghrelin was significantly ( P <0.05) increased (approx. 4 fold) with CAD, compared with NCA. The alteration of receptor density with disease for Tx and ghrelin provides novel therapeutic targets for the treatment of atherosclerosis. In conclusion, while some GPCR are altered, others remain unchanged with human atherosclerosis. The increase in vasoconstrictor Tx receptor density with disease suggests the importance of Tx receptor antagonism. Intriguingly, the increase in receptor density for the novel vasodilator ghrelin, identified from post-genomic research, may potentially be beneficial with human atherosclerosis.

1. Myocardial thromboxane A 2 production increases in patients with pacing-induced ischaemia and correlates with a decrease in myocardial lactate extraction. The release of myocardial thromboxane A 2 before any lactate production was observed in patients with unstable angina. This study was proposed to clarify whether the early thromboxane A 2 release contributed to the ongoing myocardial ischaemia and to determine which metabolites can be attributed to the thromboxane A 2 release. Thirty-five patients with chest pain and positive treadmill exercise test underwent atrial pacing to the predicted maximal heart rate. The pacing was maintained at this peak rate for 10 min, then ceased. Blood samples of the ascending aorta and coronary sinus were drawn simultaneously at rest, at 2 and 10 min of peak-pacing, and 5 and 10 min after termination of the pacing; samples were used for analyses of lipid profiles, prostacyclin, thromboxane A 2 , lactate and lipid peroxides on plasma and low-density lipoprotein particles. 2. Twenty out of 35 patients who displayed pacing-induced ischaemia were documented by electrocardiographic evidence of ST depression >2 mm developing after 2 min of peak-pacing [ischaemic group, STΔ(+)]. They had (i) negative fractional lactate extraction; (ii) pacing-induced decreases of plasma thromboxane A 2 levels in the coronary sinus blood (564 ± 57 versus 479 ± 47 ng/l, P < 0.05) at 2 min of peak-pacing; the data increased at 10 min of peak-pacing (564 ± 57 versus 620 ± 60 ng/l, P < 0.05), then returned to baseline levels at 5 and 10 min post-pacing; (iii) significantly increased lipid peroxides on low-density lipoprotein of the coronary sinus blood at 2 and 10 min of peak-pacing (each P < 0.001), as well as at 5 min post-pacing ( P < 0.05); (iv) significant correlation between thromboxane A 2 levels and lipid peroxides on low-density lipoprotein of the coronary sinus blood samples. 3. In STΔ(+) patients, myocardial thromboxane synthesis changed before lactate production and correlated with the increase of lipid peroxides on low-density lipoprotein of the coronary venous blood. This implies that lipid peroxides on low-density lipoprotein participate in thromboxane production and play a determinative role in pacing-induced ischaemia.

1. Urinary levels of the 2,3-dinor metabolites of thromboxane A 2 (2,3-dinor-thromboxane A 2 , Tx-M) and prostacyclin (2,3-dinor-6-keto-prostaglandin F 1α , PGI-M) are frequently analysed as indices of platelet and endothelial activity and interaction in vivo. Despite this, little is known about the possible diurnal variations in urinary Tx-M and PGI-M in healthy human subjects, and how the urinary levels of Tx-M and PGI-M in single samples reflect their respective 24 h excretion rates. We addressed this by determining Tx-M, PGI-M and creatinine in consecutive portions of urine collected during 24 h in 15 healthy non-smoking subjects. 2. The total 24 h excretion of Tx-M and PGI-M did not differ between men (223 ± 31 and 132 ± 27 ng, respectively) and women (215 ± 44 and 127 ± 29 ng, respectively). Neither the excretion of Tx-M nor that of PGI-M displayed any significant diurnal variation. 3. The excretion of Tx-M during a 3 h period and the Tx-M/creatinine ratio in a urine sample accurately reflected the 24 h excretion of Tx-M (correlation coefficient ranges 0.74–0.94 and 0.74–0.86, respectively). The excretion of PGI-M during a 3 h period and the PGI-M/creatinine ratio in a urinary sample were accurate measures of 24 h excretion of PGI-M (correlation coefficient ranges 0.76–0.94 and 0.72–0.83, respectively). Urinary Tx-M and PGI-M expressed as simple concentrations were poor indices of their respective 24 h excretion. 4. We conclude that time-related excretions of Tx-M and PGI-M may be the best indices ex vivo of the cardiovascular formation of thromboxane A 2 and prostacyclin, but that urinary creatinine-related concentrations of Tx-M and PGI-M in a urine sample are accurate measures as well.

1. The aim of this investigation was to study the role of prostaglandins in the impaired Na + conservation of the ageing kidney. 2. We measured the urinary excretion of thromboxane B 2 , 6-keto-prostaglandin F 1α and prostaglandin E 2 in young (3–4 months) and old (20–21 months) rats after 12, 24 and 36 h of Na + deprivation. In a separate protocol, we measured prostanoid synthesis by isolated glomeruli, cortical homogenates, medullary slices and papillary slices from young and old rats in basal conditions and after 15 days of dietary Na + deprivation. 3. In the acute study, urinary excretion of 6-ketoprostaglandin F 1α and prostaglandin E 2 decreased in young but not in old rats. Urinary excretion of prostaglandin E 2 was lower in old rats, but did not vary significantly with Na + deprivation. 4. In old rats, thromboxane B 2 synthesis was increased in all the portions of the kidney except the medulla. Production of 6-keto-prostaglandin F 1α was elevated in glomeruli and tended to increase in the cortex. Prostaglandin E 2 synthesis was also elevated in the cortex. Thromboxane B 2 synthesis tended to increase in the medulla and was enhanced in the papilla. After Na + deprivation, only glomerular prostaglandin E 2 synthesis increased in young rats. In old rats, cortical and papillary synthesis of 6-ketoprostaglandin F 1α increased, whereas prostaglandin E 2 synthesis did not change. 5. The results suggest increased thromboxane synthesis in the ageing kidney. Increased prostacyclin and prostaglandin E 2 synthesis may be an attempt to counteract enhanced thromboxane production. Blunting of this tendency in medulla and papilla could contribute to the conservation of medullary solute concentration, whereas inappropriate stimulation of prostacyclin synthesis during Na + deprivation could impair Na + conservation.

1. After bilateral ureteral obstruction there is an enhanced production of thromboxane A 2 by the kidney which contributes to a decline in renal function. An acute interstitial macrophage infiltrate also occurs. 2. The relative contribution of infiltrating cells and intrinsic renal cells to the enhanced production of thromboxane A 2 by the hydronephrotic kidney were determined. The effects of both irradiation and subsequent administration of the thromboxane synthesis inhibitor OKY-046 on both thromboxane B 2 excretion and renal function were examined in rats with 24 h bilateral ureteral obstruction. 3. Irradiation effectively prevented the leucocyte infiltrate after bilateral ureteral obstruction (1.2 ± 0.8 × 10 5 versus 27.1 ± 0.1 × 10 5 cells/g of cortex, n = A in each group), resulted in a significantly higher inulin clearance (2.78 ± 0.27 versus 1.49 ± 0.17 ml min −1 kg −1 body weight, n = 7 and n = 8, respectively, P < 0.001) and reduced thromboxane B 2 excretion to 39% of non-irradiated values. Subsequent administration of OKY-046 to previously irradiated animals further reduced thromboxane B 2 excretion to 20% of the value in non-irradiated rats with bilateral obstruction and further increased inulin clearance to 3.34 ± 0.26 ml min −1 kg −1 body weight. 4. Glomerular macrophage numbers were decreased after bilateral ureteral obstruction (in contrast to the interstitium). However, glomeruli isolated from rats with 24 h bilateral ureteral obstruction exhibited enhanced production of thromboxane B 2 compared with sham-operated control rats (855.6 ± 31.1 versus 392.2 ± 25.5 pg 60 min −1 mg −1 of protein, P < 0.001). 5. These data suggest that the increased renal production of thromboxane A 2 after bilateral ureteral obstruction results from both renal infiltration by metabolically active macrophages and enhanced prostanoid production by the glomeruli. Both sources of thromboxane A 2 contribute to altered renal function after bilateral ureteral obstruction.

1. The burst of damaging oxygen free-radicals at the time of reperfusion is one of the crucial factors affecting skin flap survival after an ischaemic interval. In these experiments the efficacy of the antioxidant and free-radical scavenger N -acetylcysteine in improving the survival of ischaemic rabbit epigastric skin flaps was tested. 2. At the time of reperfusion flaps were given: (1) balanced salt solution by intravenous whole-body administration, (2) N -acetylcysteine (200 mg/kg) by intravenous whole-body administration, (3) balanced salt solution by intra-arterial infusion into the flap, (4) N -acetylcysteine (20 mg/kg) by intra-arterial infusion into the flap, or (5) N -acetylcysteine (200 mg/kg) by intra-arterial infusion into the flap. Flap survival at 1 week, and tissue levels of parameters related to free-radical production, blood levels of thromboxane B 2 and peripheral resistance during reperfusion were determined. 3. Compared with controls (groups 1 and 3) which had flap survival rates (expressed as percentage surface area surviving) of 27.1% and 31.6%, respectively, N -acetylcysteine treatment in group 2 (55.2%) and group 4 (51.9%) resulted in significant ( P < 0.05) improvements in flap survival. The survival rate in group 5 (37.7%) was not significantly better than that of the controls. 4. N -Acetylcysteine significantly reduced parameters related to free-radical production in the skin flap after 30 min of reperfusion, determined as tissue levels of malonyldialdehyde and protein oxidation products. There was also a significant decrease in peripheral resistance when low-dose N -acetylcysteine (group 4) was infused intra-arterially into the flap. The systemic levels of thromboxane B 2 , a prostanoid promoting thrombosis, were not significantly altered by administration of N -acetylcysteine. 5. N -Acetylcysteine proved to be a successful therapeutic agent for the salvage of experimental ischaemic rabbit skin flaps, when used as a low-dose intra-arterial or high-dose intravenous treatment. The possible clinical benefits in humans have yet to be demonstrated.

1. Cigarette smoking is known to increase the risk of cardiovascular disease in both men and women. Experimental and epidemiological studies have demonstrated that cigarette smoking is associated with several indices of increased platelet activation and platelet/vessel wall interaction in men. The aim of the present study was to test the hypothesis that cigarette smoking is linked to an increased platelet activity in women also. 2. In 26 healthy smoking and non-smoking women (age 21–49 years) the urinary excretion of the thromboxane A 2 metabolite 2,3-dinor-thromboxane B 2 (an index of platelet activation) and of the prostacyclin metabolite 2,3-dinor-6-keto-prostaglandin F 1α (an index of platelet/vessel wall interaction) were analysed by g.c.-m.s. in samples collected on days 3, 10 and 20 of their respective menstrual cycles. 3. The urinary excretion of 2,3-dinor-thromboxane B 2 did not vary significantly during the menstrual cycle, either in the smokers or in the non-smokers. It was consistently higher ( P < 0.004) in the group of smokers (average of days 3, 10 and 20, 395 ± 61 pg/mg of creatinine; mean ± sem ) than in the group of non-smokers (average 188 ± 22 pg/mg of creatinine). 4. The urinary excretion of 2,3-dinor-6-keto-prostaglandin F 1α did not differ between the groups on any of the days studied (average on days 3, 10 and 20 in the smokers and non-smokers was 281 ± 50 and 227 ± 30 pg/mg of creatinine, respectively). 5. These data demonstrate that smoking fertile women excrete more of the thromboxane A 2 metabolite than do non-smokers, thereby supporting the hypothesis that cigarette smoking elicits platelet activation in healthy women. In contrast, platelet/vessel wall interaction does not appear to be facilitated in smoking compared with non-smoking women. The data suggest that platelet activation is not a major haemostatic mechanism during menstruation.

1. Biochemical mechanisms of ischaemia were investigated in rabbit skin flaps subjected to 2 h of primary ischaemia then, 24 h later, to 4 h of secondary ischaemia. During secondary ischaemia, flaps underwent either total ischaemia (arterial and venous blood supply occluded) or partial ischaemia (vein only occluded). Some of these flaps were treated at the time of reperfusion with the free-radical scavenger superoxide dismutase (EC 1.15.1.1) and/or the thromboxane synthetase inhibitor UK-38,485. 2. After 30 min of reperfusion, superoxide dismutase treatment significantly reduced blood thromboxane levels, elevated during ischaemia. Superoxide dismutase also reduced tissue levels of malonyldialdehyde and xanthine oxidase, indicators of free-radical damage, and restored the depleted tissue levels of superoxide dismutase. 3. UK-38,485 treatment failed to significantly alter any of these tissue free-radical parameters, although this agent significantly reduced blood thromboxane levels. 4. Combined superoxide dismutase plus UK-38,485 treatment was not significantly better than either treatment alone with respect to any parameter. 5. Partial ischaemia led to consistently higher levels of tissue free radicals and blood thromboxane than did total ischaemia. Thus partial ischaemia appears to result in greater free-radical damage than total ischaemia. 6. These results are consistent with the hypothesis that thromboxane acts as a mediator for free-radical damage in the ischaemic changes within the flap.

1. The inhibitory effects of aspirin on platelet function in vitro have been shown to be both time (over 3 h) and concentration (1–10 μmol/l) dependent. 2. To determine if these effects occurred in vivo , four volunteers received intravenous infusions on four occasions, to give constant plasma aspirin concentrations of 0, 1, 2 and 4 μmol/l over 3 h. Infusions were performed at intervals of at least 2 weeks. 3. Before and during the infusions, blood was taken for assay of aspirin concentrations, and measurements of platelet aggregation in response to collagen, adenosine 5′-pyrophosphate and arachidonate. Thromboxane generation after stimulated platelet aggregation and whole-blood coagulation was also measured. 4. At each aspirin concentration, both platelet aggregation and thromboxane generation in response to collagen and arachidonate were inhibited progressively over the 3 h infusion period. Greatest inhibition was seen during the 4 μmol/l infusion, which produced maximal or near-maximal inhibition by the third hour. 5. Thromboxane generated during whole-blood coagulation was similarly inhibited in both a time- and concentration-dependent manner throughout all aspirin infusions. 6. The progressive nature of the inhibition of platelet function with these low aspirin concentrations may be due to either slow aspirin transport across the platelet membrane or delayed interaction with cyclo-oxygenase.

1. At present it is unclear whether platelet-activating-factor (PAF)-induced aggregation is mediated by thromboxane. To obtain further information about this event we have compared the affects of aspirin on platelet aggregation and secretion induced by PAF and collagen. 2. Collagen and PAF induced aggregation and secretion in human platelets in a dose-related manner. 3. Aspirin inhibited the magnitude of both platelet aggregation and secretion induced by PAF and collagen, but the degree of inhibition was much greater for collagen. 4. Aspirin strongly inhibited the aggregation rate of collagen-induced platelet aggregation, but had no measurable effect on the rate of PAF-induced aggregation. 5. Inconsistencies reported in previous studies of the effect of aspirin on PAF-induced platelet aggregation may be explained, in part, by the doses of PAF used and the method of inactivating cyclo-oxygenase ( in vitro compared with in vivo ). 6. Our results suggest that the initial events of PAF-induced aggregation are independent of thromboxane A 2 formation and that thromboxane A 2 plays only a minor role in the later phase of PAF-induced aggregation.

1. The synthesis of prostaglandin (PG) E 2 , PGF 2α , 6-keto-PGF 1α and thromboxane (TX) B 2 by isolated glomeruli, cortical tubules, inner medullary slices and outer medullary slices was measured in salt-depleted (LNa) rats and in salt-depleted rats receiving captopril (LNa-CEI). Animals were studied before and after 4, 9 and 15 days of Na + depletion. 2. Na + balance was reached in LNa rats after 4 days. Blood pressure and creatinine clearance remained stable. Serum Na + decreased from 140 ± 1 to 126 ± 1 mmol/l (mean ± sem , P < 0.01). In contrast, LNa-CEI rats were unable to conserve Na + adequately: fractional excretion of Na + and natriuresis were constantly greater than in LNa animals. As a consequence, LNa-CEI rats developed severe hyponatremia, lost weight and their creatinine clearance decreased. 3. The glomerular synthesis of PGE 2 , PGF 2α and 6-keto-PGF 1α , but not of TXB 2 , was significantly increased in LNa rats. In LNa-CEI rats, the synthesis of PGE 2 and 6-keto-PGF 1α was similar to control values, but PGF 2α and TXB 2 synthesis was elevated at day 9. In cortical tubules, PGE 2 and PGF 2α were unaffected by Na + depletion, but 6-keto-PGF 1α and TXB 2 were increased and a similar trend was observed in LNa-CEI rats. In outer medulla of LNa rats, a decrease in all the eicosanoids measured was observed at day 4. In LNa-CEI animals, the synthesis of PGE 2 and PGF 2α , but not of 6-keto-PGF 1α and TXB 2 , was significantly depressed. In inner medulla, Na + depletion only tended to decrease PGF 2α and 6-keto-PGF 1α , but in the presence of captopril, the synthesis of all prostanoids was significantly decreased.

1. The aspirin concentrations previously reported to inhibit platelet aggregation in vitro (40–500 μmol/l) are much greater than those required in vivo in man (5 μmol/l). 2. Human platelet-rich plasma was incubated with buffer or various aspirin concentrations at 37°C for up to 4.5 h. Platelet aggregation and thromboxane generation were measured in response to collagen (0.4–6.3 μg/ml) and adenosine 5′-pyrophosphate (0.5–4 μmol/l). 3. The concentration of aspirin needed to inhibit platelet aggregation in response to a critical concentration of aggregating agent (lowest concentration to cause greater than 50% aggregation) was lower than that required for higher concentrations of aggregating agent. 4. With more prolonged incubation times with aspirin, lower concentrations of aspirin inhibited platelet aggregation. 5. Inhibition of platelet aggregation and thromboxane formation by 10 μmol/l aspirin was maximal by 90 min. There was progressive inhibition by 3 μmol/l aspirin during incubation for 270 min. By the end of this time there was also significant inhibition by 1 μmol/l aspirin. 6. The apparent discrepancy between inhibitory aspirin concentrations in vivo and those observed in vitro in previous studies appears to have been resolved by extending the incubation time of platelets with low aspirin concentrations, thus mimicking the conditions in vivo .

1. Eleven healthy, unanaesthetized sheep were given either a single intravenous bolus infusion of U63,577A (Upjohn), a selective thromboxane synthetase inhibitor, at a dose of 30 mg/kg (group 1, n = 6), or vehicle alone (group 2, n = 5). Animals were maintained in metabolic cages during the study, and received 150 ml of water/h and 7.5 mmol of sodium/h as Ringers lactate by intravenous infusion for 24 h before and during the study. During two 1 h control urine collections via bladder catheter, urine volume and sodium excretion closely paralleled these infusion rates. 2. In the first hour after injection of U63,577A, there were significant two- to three-fold increases in urine volume, urinary sodium excretion and fractional sodium excretion, compared with the control collections. During the subsequent 4 h, urine volume, urinary sodium excretion, and fractional sodium excretion fell to values significantly lower than in the control period. Creatinine clearance was reduced 1, 2 and 4 h post injection and returned to control values at 5 h. Urinary excretion of thromboxane B 2 was significantly reduced compared with control values during the 5 h after injection of U63,577A. Excretion of 6-keto-prostaglandin F 1α did not change. Plasma renin activity was significantly increased 1, 3 and 5 h after injection of U63,577A. Vehicle controls showed no change in any of the above parameters. 3. The results indicate that in healthy conscious sheep, sodium and water replete, U63,577A has a transient but significant diuretic and natriuretic effect, followed by sodium and water retention and increased plasma renin activity. The results may reflect an antidiuretic/antinatriuretic effect of thromboxane A 2 , or possibly diversion of cyclic endoperoxides into formation of vasodilator/natriuretic prostaglandins. These effects might be exaggerated and/or modified in conditions where arachidonic acid metabolism is stimulated.

1. The fatty acid composition of membrane phospholipids of stimulated and unstimulated platelets was studied in six normal volunteers given a daily dietary supplement of a fish oil rich in eicosapentaenoic acid (EPA) for 4 weeks. The supplement was equivalent to 1.8 g of EPA daily. Thromboxane synthesis and platelet aggregation responses to sodium arachidonate, thrombin and the ionophore A23187 were also investigated. 2. A marked increase in the relative EPA content of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was noted after 2 and 4 weeks fish oil supplementation. However, there was no incorporation into phosphatidylinositol (PI) or phosphatidylserine (PS). The relative arachidonic acid (AA) content of PC and PE was significantly reduced at 2 and 4 weeks but that of PI and PS remained unchanged. Significant reductions in the relative linoleic acid content of total phospholipids, PC and PE were also noted. 3. Stimulation of platelets obtained after 4 weeks fish oil supplementation by thrombin and A23187 was associated with a marked reduction in the AA content of PI and a minor reduction in that of PE. There was no change in the relative proportions of EPA in PI, PS, PC or PE after stimulation. Throughout the study there were no significant changes in platelet aggregation responses or in platelet thromboxane production. 4. Our results indicate that the incorporation of EPA into the platelet membrane phospholipids is selective and that if PI is the major source of AA for platelet prostaglandin biosynthesis then the reported beneficial effects of EPA on haemostasis cannot be explained on the basis of its incorporation into and mobilization from the platelet membrane phospholipid pool.

1. Levels of immunoreactive 6-oxo-prostaglandin F 1α (6-oxo-PGF 1α ) and thromboxane B 2 (TXB 2 ) were measured in peripheral venous plasma in a group of volunteers and non-insulin dependent diabetic patients (NIDDS). Levels of these eicosanoids were close to the limit of sensitivity of the radioimmunoassays and consequently data are reported as maximal values. Basal plasma levels of 6-oxo-PGF 1α did not exceed 5 pg/ml in either group and maximal levels of immunoreactive TXB 2 were 125 ± 14 and 128 ± 8 pg/ml for volunteers and NIDDS respectively. 2. Attempts to elicit peripheral vascular prostacyclin biosynthesis in volunteers by using forearm ischaemia produced no increase in plasma 6-oxo-PGF 1α levels. Measurement of the combined plasma levels of 6-oxo-PGF 1α , 13,14-dihydro-6-oxo-PGF 1α , 13,14-dihydro-6,15-dioxo-PGF 1α and 6-oxo-PGE 1 indicated that these were also low (less than 5 pg/ml) and that failure to demonstrate increased 6-oxo-PGF 1α levels was unlikely to have arisen from metabolism of prostacyclin to one or more of these metabolites. 3. Measurement of 6-oxo-PGF 1α and TXB 2 in peripheral venous plasma before and during chloropropamide alcohol flushing (CPAF) did not provide evidence for a role for these eicosanoids in the etiology of this phenomenon. 4. These findings point to the need for a reappraisal of studies that have described altered plasma levels of 6-oxo-PGF 1α and TXB 2 in CPAF and other pathophysiological conditions in man.