The RAS (renin–angiotensin system) plays an important role in the pathophysiology of CVD (cardiovascular disease), and RAS blockade is an important therapeutic strategy in the management of CVD. A new counterbalancing arm of the RAS is now known to exist in which ACE (angiotensin-converting enzyme) 2 degrades Ang (angiotensin) II, the main effector of the classic RAS, and generates Ang-(1–7). Altered ACE2 expression is associated with cardiac and vascular disease in experimental models of CVD, and ACE2 is increased in failing human hearts and atherosclerotic vessels. In man, circulating ACE2 activity increases with coronary heart disease, as well as heart failure, and a large proportion of the variation in plasma ACE2 levels has been attributed to hereditary factors. The ACE2 gene maps to chromosome Xp22 and this paper reviews the evidence associating ACE2 gene variation with CVD and considers clues to potential functional ACE2 variants that may alter gene expression or transcriptional activity. Studies to date have investigated ACE2 gene associations in hypertension, left ventricular hypertrophy and coronary artery disease, but the results have been inconsistent. The discrepancies may reflect the sample size of the studies, the gender or ethnicity of subjects, the cardiovascular phenotype or the ACE2 SNP investigated. The frequent observation of apparent sex-dependence might be of special importance, if confirmed. As yet, there are no studies to concurrently assess ACE2 gene polymorphisms and circulating ACE2 activity. Large-scale carefully conducted clinical studies are urgently needed to clarify more precisely the potential role of ACE2 in the CVD continuum.

The RAS (renin–angiotensin system) is activated after MI (myocardial infarction), and RAS blockade with ACEis [ACE (angiotensin-converting enzyme) inhibitors] or ARBs (angiotensin receptor blockers) slows but does not completely prevent progression to heart failure. Cardiac ACE is increased after MI and leads to the formation of the vasoconstrictor AngII (angiotensin II). The enzyme ACE2 is also activated after MI and degrades AngII to generate the vasodilator Ang-(1–7) [angiotensin-(1–7)]. Overexpression of ACE2 offers cardioprotective effects in experimental MI, but there is conflicting evidence as to whether the benefits of ACEis and ARBs are mediated through increasing ACE2 after MI. In the present study, we assessed the effect of an ACEi and ARB, alone and in combination, on cardiac ACE2 in a rat MI model. MI rats received vehicle, ACEi (ramipril; 1 mg/kg of body weight), ARB (valsartan; 10 mg/kg of body weight) or combination (ramipril at 1 mg/kg of body weight and valsartan at 10 mg/kg of body weight) orally for 28 days. Sham-operated rats were also studied and received vehicle alone. MI increased LV (left ventricular) mass ( P <0.0001), impaired cardiac contractility ( P <0.05) and activated cardiac ACE2 with increased gene ( P <0.05) and protein expression (viable myocardium, P <0.05; border zone, P <0.001; infarct, P <0.05). Ramipril and valsartan improved remodelling ( P <0.05), with no additional effect of dual therapy. Although ramipril inhibited ACE, and valsartan blocked the angiotensin receptor, neither treatment alone nor in combination augmented cardiac ACE2 expression. These results suggest that the cardioprotective effects of ramipril and valsartan are not mediated through up-regulation of cardiac ACE2. Strategies that do augment ACE2 after MI may be a useful addition to standard RAS blockade after MI.

The RAS (renin–angiotensin system) is now recognized as an important regulator of liver fibrosis and portal pressure. Liver injury stimulates the hepatic expression of components of the RAS, such as ACE (angiotensin-converting enzyme) and the AT 1 receptor [AngII (angiotensin II) type 1 receptor], which play an active role in promoting inflammation and deposition of extracellular matrix. In addition, the more recently recognized structural homologue of ACE, ACE2, is also up-regulated. ACE2 catalyses the conversion of AngII into Ang-(1–7) [angiotensin-(1–7)], and there is accumulating evidence that this ‘alternative axis’ of the RAS has anti-fibrotic, vasodilatory and anti-proliferative effects, thus counterbalancing the effects of AngII in the liver. The RAS is also emerging as an important contributor to the pathophysiology of portal hypertension in cirrhosis. Although the intrahepatic circulation in cirrhosis is hypercontractile in response to AngII, resulting in increased hepatic resistance, the splanchnic vasculature is hyporesponsive, promoting the development of the hyperdynamic circulation that characterizes portal hypertension. Both liver fibrosis and portal hypertension represent important therapeutic challenges for the clinician, and there is accumulating evidence that RAS blockade may be beneficial in these circumstances. The present review outlines new aspects of the RAS and explores its role in the pathogenesis and treatment of liver fibrosis and portal hypertension.

Deficiency of ACE2 (angiotensin-converting enzyme 2), which degrades Ang (angiotensin) II, promotes the development of glomerular lesions. However, the mechanisms explaining why the reduction in ACE2 is associated with the development of glomerular lesions have still to be fully clarified. We hypothesized that ACE2 may regulate the renoprotective actions of ANP (atrial natriuretic peptide). The aim of the present study was to investigate the effect of ACE2 deficiency on the renal production of ANP. We evaluated molecular and structural abnormalities, as well as the expression of ANP in the kidneys of ACE2-deficient mice and C57BL/6 mice. We also exposed renal tubular cells to AngII and Ang-(1–7) in the presence and absence of inhibitors and agonists of RAS (renin–angiotensin system) signalling. ACE2 deficiency resulted in increased oxidative stress, as well as pro-inflammatory and profibrotic changes. This was associated with a down-regulation of the gene and protein expression on the renal production of ANP. Consistent with a role for the ACE2 pathway in modulating ANP, exposing cells to either Ang-(1–7) or ACE2 or the Mas receptor agonist up-regulated ANP gene expression. This work demonstrates that ACE2 regulates renal ANP via the generation of Ang-(1–7). This is a new mechanism whereby ACE2 counterbalances the renal effects of AngII and which explains why targeting ACE2 may be a promising strategy against kidney diseases, including diabetic nephropathy.

ACE (angiotensin-converting enzyme) 2 is expressed in the heart and kidney and metabolizes Ang (angiotensin) II to Ang-(1–7) a peptide that acts via the Ang-(1–7) or mas receptor. The aim of the present study was to assess the effect of Ang-(1–7) on blood pressure and cardiac remodelling in a rat model of renal mass ablation. Male SD (Sprague–Dawley) rats underwent STNx (subtotal nephrectomy) and were treated for 10 days with vehicle, the ACE inhibitor ramipril (oral 1 mg·kg −1 of body weight·day −1 ) or Ang-(1–7) (subcutaneous 24 μg·kg −1 of body weight·h −1 ) (all n = 15 per group). A control group ( n = 10) of sham-operated rats were also studied. STNx rats were hypertensive ( P <0.01) with renal impairment ( P <0.001), cardiac hypertrophy ( P <0.001) and fibrosis ( P <0.05), and increased cardiac ACE ( P <0.001) and ACE2 activity ( P <0.05). Ramipril reduced blood pressure ( P <0.01), improved cardiac hypertrophy ( P <0.001) and inhibited cardiac ACE ( P <0.001). By contrast, Ang-(1–7) infusion in STNx was associated with further increases in blood pressure ( P <0.05), cardiac hypertrophy ( P <0.05) and fibrosis ( P <0.01). Ang-(1–7) infusion also increased cardiac ACE activity ( P <0.001) and reduced cardiac ACE2 activity ( P <0.05) compared with STNx-vehicle rats. Our results add to the increasing evidence that Ang-(1–7) may have deleterious cardiovascular effects in kidney failure and highlight the need for further in vivo studies of the ACE2/Ang-(1–7)/ mas receptor axis in kidney disease.

Alterations within the RAS (renin–angiotensin system) are pivotal for the development of renal disease. ACE2 (angiotensin-converting enzyme 2) is expressed in the kidney and converts the vasoconstrictor AngII (angiotensin II) into Ang-(1–7), a peptide with vasodilatory and anti-fibrotic actions. Although the expression of ACE2 in the diabetic kidney has been well studied, little is known about its expression in non-diabetic renal disease. In the present study, we assessed ACE2 in rats with acute kidney injury induced by STNx (subtotal nephrectomy). STNx and Control rats received vehicle or ramipril (1 mg·kg −1 of body weight·day −1 ), and renal ACE, ACE2 and mas receptor gene and protein expression were measured 10 days later. STNx rats were characterized by polyuria, proteinuria, hypertension and elevated plasma ACE2 activity (all P <0.01) and plasma Ang-(1–7) ( P <0.05) compared with Control rats. There was increased cortical ACE binding and medullary mas receptor expression ( P <0.05), but reduced cortical and medullary ACE2 activity in the remnant kidney ( P <0.05 and P <0.001 respectively) compared with Control rats. In STNx rats, ramipril reduced blood pressure ( P <0.01), polyuria ( P <0.05) and plasma ACE2 ( P <0.01), increased plasma Ang-(1–7) ( P <0.001), and inhibited renal ACE ( P <0.001). Ramipril increased both cortical and medullary ACE2 activity ( P <0.01), but reduced medullary mas receptor expression ( P <0.05). In conclusion, our results show that ACE2 activity is reduced in kidney injury and that ACE inhibition produced beneficial effects in association with increased renal ACE2 activity. As ACE2 both degrades AngII and generates the vasodilator Ang-(1–7), a decrease in renal ACE2 activity, as observed in the present study, has the potential to contribute to the progression of kidney disease.

Ang-(1–7) (angiotensin-1–7), a peptide product of the recently described ACE (angiotensin-converting enzyme) homologue ACE2, opposes the harmful actions of AngII (angiotensin II) in cardiovascular tissues, but its role in liver disease is unknown. The aim of the present study was to assess plasma levels of Ang-(1–7) in human liver disease and determine its effects in experimental liver fibrosis. Angiotensin peptide levels were measured in cirrhotic and non-cirrhotic patients with hepatitis C. The effects of Ang-(1–7) on experimental fibrosis were determined using the rat BDL (bile-duct ligation) model. Liver histology, hydroxyproline quantification and expression of fibrosis-related genes were assessed. Expression of RAS (renin–angiotensin system) components and the effects of Ang-(1–7) were examined in rat HSCs (hepatic stellate cells). In human patients with cirrhosis, both plasma Ang-(1–7) and AngII concentrations were markedly elevated ( P <0.001). Non-cirrhotic patients with hepatitis C had elevated Ang-(1–7) levels compared with controls ( P <0.05), but AngII concentrations were not increased. In BDL rats, Ang-(1–7) improved fibrosis stage and collagen Picrosirius Red staining, and reduced hydroxyproline content, together with decreased gene expression of collagen 1A1, α-SMA (smooth muscle actin), VEGF (vascular endothelial growth factor), CTGF (connective tissue growth factor), ACE and mas [the Ang-(1–7) receptor]. Cultured HSCs expressed AT 1 Rs (AngII type 1 receptors) and mas receptors and, when treated with Ang-(1–7) or the mas receptor agonist AVE 0991, produced less α-SMA and hydroxyproline, an effect reversed by the mas receptor antagonist A779. In conclusion, Ang-(1–7) is up-regulated in human liver disease and has antifibrotic actions in a rat model of cirrhosis. The ACE2/Ang-(1–7)/ mas receptor axis represents a potential target for antifibrotic therapy in humans.

The aim of the present study was to determine the prevalence and predictors of an abnormal echocardiogram in patients with Type 2 diabetes. Cardiac function and structure were rigorously assessed by comprehensive transthoracic echocardiographic techniques in 229 patients with Type 2 diabetes. Cardiovascular risk factors and diabetic complications were assessed, and predictors of an abnormal echocardiogram were identified using multivariate logistic regression analysis. An abnormal echocardiogram was present in 166 patients (72%). LVH (left ventricular hypertrophy) occurred in 116 patients (51%), and cardiac dysfunction was found in 146 patients (64%), of whom 109 had diastolic dysfunction alone and 37 had systolic±diastolic dysfunction. Independent predictors of an abnormal echocardiogram were obesity, age, the number of antihypertensive drugs used (all P <0.001) and creatinine clearance ( P <0.05). The risk of an abnormal echocardiogram increased by 9% for each year over 50 years of age {OR (odds ratio), 1.09 [95% CI (confidence interval), 1.04–1.15]}, 3-fold if obesity was present [BMI (body mass index) >30; OR, 4.2 (95% CI, 1.9–9.0)] and by 80% for each antihypertensive agent used [OR, 1.8 (95% CI, 1.3–2.4) per agent]. In conclusion, an abnormal cardiac echocardiogram is common in patients with Type 2 diabetes. Importantly, although cardiac abnormalities can be predicted by traditional risk factors, such as age, obesity and renal function, the absence of micro- or macro-vascular complications does not predict a normal echocardiogram. We suggest that an echocardiogram identifies those with Type 2 diabetes at increased cardiovascular risk due to occult LVH and diastolic dysfunction, and this information may lead to more aggressive management of known risk factors in the clinic.

Anaemia is common in patients with diabetes and associated with an increased risk of diabetic complications. Although the role of anaemia in heart failure is established, we hypothesize that anaemia also contributes to an increased risk of cardiac dysfunction in patients with Type II diabetes. In the present study, 228 consecutive adults with diabetes were investigated using transthoracic echocardiography. Echocardiographic parameters were correlated with the Hb (haemoglobin) level and adjusted for other risk factors for cardiac dysfunction using multivariate analysis. More than one in five patients (23%) had anaemia, which was an independent risk factor for cardiac dysfunction on echocardiography. Over one-third of all patients with evidence of abnormal cardiac function (diastolic and/or systolic dysfunction) on echocardiography had anaemia compared with <5% of patients with normal echocardiographic findings. Most patients with anaemia had cardiac dysfunction (94%), with the major abnormality being diastolic dysfunction associated with an increased left ventricular mass and impaired relaxation indices. A continuous association between diastolic function and Hb was also observed in patients without anaemia. In patients with a history of cardiovascular disease, systolic dysfunction was twice as common in patients with anaemia. Anaemia was also correlated with plasma markers of cardiac risk, including BNP (brain natriuretic peptide), CRP (C-reactive protein) and AVP (arginine vasopressin). Notably, the predictive utility of these markers was eliminated after adjusting for Hb. Consequently, the inexpensive measurement of Hb may be a useful tool to identify diabetic patients at increased risk of cardiac dysfunction.

Vasopeptidase inhibitors simultaneously inhibit angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The present study characterized the tissue distributions of ACE and NEP, and assessed the effects of the vasopeptidase inhibitor omapatrilat on ACE and NEP in rat tissues. In vivo ACE and NEP inhibition was studied by in vitro autoradiography and using the ACE inhibitor radioligand 125 I-MK351A and the NEP inhibitor radioligand 125 I-RB104 in rats that received oral omapatrilat (40 mg·day -1 ·kg -1 ) for 3 days. In vitro autoradiography was used to examine the distribution of ACE and NEP in the kidney, aorta, heart, adrenal gland, lung, intestine, liver, spleen and brain, and to assess enzyme inhibition after oral omapatrilat. Omapatrilat inhibited plasma ACE and increased plasma renin activity ( P <0.01). Tissue ACE was inhibited by 70–95% ( P <0.01), except in the brain, where ACE was not inhibited. NEP was inhibited by 87% in the kidney and by 20–40% in atria, aorta, adrenal gland, lung, liver and intestine; it was not inhibited in the brain, the ventricle or the spleen. Omapatrilat is a potent vasopeptidase inhibitor that significantly inhibits tissue ACE and NEP, with the degree of inhibition varying according to the enzyme and the tissue under assessment. The degree and site of tissue enzyme inhibition by vasopeptidase inhibitors may be relevant to end-organ protection as well as to the side-effect profiles of these agents.

The aim of the present study was to compare the antihypertrophic effects of blockade of the renin–angiotensin system (RAS), vasopeptidase inhibition and calcium channel antagonism on cardiac and vascular hypertrophy in diabetic spontaneously hypertensive rats (SHR). SHR with streptozotocin-induced diabetes were treated with one of the following therapies for 32 weeks: the angiotensin-converting enzyme (ACE) inhibitor captopril (100mg/kg); the angiotensin AT 1 receptor antagonist valsartan (30mg/kg); a combination of captopril with valsartan; the vasopeptidase inhibitor mixanpril (100mg/kg); or the calcium channel antagonist amlodipine (6mg/kg). Systolic blood pressure and cardiac and mesenteric artery hypertrophy were assessed. Mean systolic blood pressure in diabetic SHR (200±5mmHg) was reduced by captopril (162±5mmHg), valsartan (173±5mmHg), mixanpril (176±2mmHg) and amlodipine (159±4mmHg), and was further reduced by the combination of captopril with valsartan (131±5mmHg). Captopril, valsartan and mixanpril reduced heart and left ventricle weights by approx. 10%. The combination of captopril and valsartan further reduced heart weight (-24%) and left ventricular weight (-29%). Amlodipine did not affect cardiac hypertrophy. Only mixanpril and the combination of captopril and valsartan significantly reduced mesenteric weight. The mesenteric wall/lumen ratio was reduced by all drugs, and to a greater extent by the combination of captopril and valsartan. We conclude that optimizing the blockade of vasoconstrictive pathways such as the RAS, particularly with the combination of ACE inhibition and AT 1 receptor antagonism, is associated with antitrophic effects in the context of diabetes and hypertension. In contrast, calcium channel blockade, despite similar effects on blood pressure, confers less antitrophic effects in the diabetic heart and blood vessels.

1. Inhibition of neutral endopeptidase (NEP), the degradative enzyme for atrial natriuretic peptide, was studied in vitro and in vivo using a previously characterized NEP inhibitor radioligand, 125 I-labelled RB104. 2. SCH 42354, the active di-acid of the ethylester prodrug, SCH 42495, caused a concentration-dependent displacement of 125 I-labelled RB104 from rat renal NEP. The concentration of SCH 42354 that displaced 50% of radioligand bound to the enzyme NEP (IC 50 ) was 3.3 ± 0.1 nmol/1 (mean ± SEM). Enalaprilat, an angiotensin converting enzyme inhibitor, did not displace 125 I-labelled RB104 in concentrations up to 10 μmol/1. 3. In adult normotensive Sprague—Dawley rats, oral SCH 42495 (3–300 mg/kg) caused significant inhibition of renal NEP ( P < 0.001). SCH 42495 had no effect on renal or plasma angiotensin converting enzyme activity, but high-dose SCH 42495 (300 mg/kg) caused a significant increase in plasma renin activity ( P < 0.01). 4. In a time course study, oral SCH 42495 (30 mg/kg) caused rapid (within 30 min) and significant inhibition of renal NEP for up to 48 h ( P < 0.001). No changes in plasma atrial natriuretic peptide or plasma angiotensin converting enzyme activity were seen. 5. These data provide evidence that short-term administration of the NEP inhibitor SCH 42495 results in inhibition of renal NEP and does not inhibit the circulating or the tissue renin—angiotensin system. The NEP inhibitor radioligand 125 I-labelled RB104, is a useful tool to study tissue NEP inhibition after administration of NEP inhibitors.

1. We studied the effects of the non-selective, non-peptide, orally active endothelin (ET) receptor antagonist bosentan (Ro 47–0203) on rat hepatic and mesenteric vascular membrane 125 I-ET-1 binding characteristics in vitro and ex vivo (after bosentan by gavage in vivo ). 2. Bosentan caused a concentration-dependent competitive inhibition of 125 I-ET-1 binding to female rat mesenteric vascular (predominantly ETA receptors) and hepatic (predominantly ETB receptors) membranes in vitro and ex viva 3. The time course of the inhibition of binding ex vivo after administration of bosentan in vivo was 1–4 h for mesenteric vascular (predominantly ETA receptors) binding and 1–16 h for hepatic (predominantly ETB receptors) binding. 4. The time course of displacement of 125 I-ET-1 binding from mesenteric vascular and hepatic membranes by bosentan in vitro was similar. 5. Since bosentan is significantly excreted by the liver, the prolonged hepatic 125 I-ET-1 binding by bosentan presumably represents hepatic accumulation of bosentan, which may have implications for bosentan antagonizing the actions of ET in the liver.

1. The effect of vasopressin receptor antagonists varies between analogues (peptide, non-peptide) and across species. In this study the effect of the novel non-peptide vasopressin V1a receptor antagonist SR 49059 on human internal mammary arteries was investigated. 2. SR 49059 produced a potent, concentration-dependent, inhibitory effect on vasopressin-induced contraction of human coronary bypass graft internal mammary arteries. Both SR 49059 (1 μmol/l) and a peptide selective V1a antagonist {[d(CH 2 ) 5 sarcosine 7 ]arginine vasopressin} (1 μmol/l) abolished vasopressin-induced contraction. The non-peptide V1a receptor antagonist OPC-21268 (1 μmol/l) had no effect on vasopressin-induced contraction. 3. The effect of SR 49059 was specific to vascular vasopressin receptors as noradrenaline-induced contraction was not influenced by SR 49059. 4. The results of this study in vitro indicate that the non-peptide SR 49059 is a potent, specific vasopressin V1a receptor antagonist in the human internal mammary artery and suggest that it may be a useful tool for studying the pathophysiological role of vasopressin in man.

1. To investigate the mechanism of hepatic V1a vasopressin receptor down-regulation in streptozotocin-induced diabetes mellitus in the rat, we measured hepatic V1a receptor mRNA by in situ hybridization histochemistry using oligonucleotide probes to the V1a receptor and Northern blotting. 2. Diabetes mellitus caused hyperglycaemia, hyperosmolality and increased plasma vasopressin concentrations ( P < 0.01). Hepatoycte V1a receptor mRNA was reduced by 76% in diabetic rats ( P < 0.01) and by 53% in insulin-treated diabetic rats ( P < 0.01) versus control rats, in parallel with reduced V1a radioligand binding and vasopressin-stimulated inositol phosphates production. There was a similar decrease in hepatic V1a/18S mRNA density ratio in the diabetic and diabetic + insulin groups (both P < 0.05 versus control). 3. These findings suggest that altered V1a mRNA transcription is responsible for the reduced hepatic V1a receptor density in diabetes mellitus.

1. The effects of the non-peptide arginine vasopressin V 1 receptor antagonist (OPC-21268) and the non-peptide V 2 receptor antagonist (OPC-31260) on vasopressin-induced contraction of human internal mammary arteries and rat mesenteric resistance arteries were investigated. 2. In human internal mammary arteries, the non-peptide V 1 receptor antagonist, OPC-21268, failed to antagonize vasopressin-induced contraction at low concentrations and potentiated the contraction at higher concentrations (300 nmol/l, P < 0.05). A peptide selective V 1 receptor antagonist {[d(CH 2 ) 5 , sarcosine 7 ]arginine vasopressin} potently inhibited the vasopressin-induced contraction, indicating the presence of functionally constrictor V 1 receptors in human internal mammary arteries. Both peptide (desGly-NH 2 9 [d(CH 2 ) 5 , D-Ile 2 , Ile 4 ]arginine vasopressin) and non-peptide ‘selective’ V 2 receptor antagonists (OPC-31260, 3 μmol/l) significantly antagonized vasopressin-induced contraction ( P < 0.01), indicating partial V 1 receptor antagonist activity. 3. The vasopressin-induced contraction in human internal mammary arteries was reversed by high concentrations of the non-peptide V 2 receptor antagonist, OPC-31260, but not by the non-peptide V 1 receptor antagonist, OPC-21268. 5. In rat mesenteric resistance arteries, both OPC-21268 (10 nmol/l) and OPC-31260 (1 μmol/l) antagonized vasopressin-induced contraction ( P < 0.01). 6. The results of this study in vitro indicate that in human internal mammary arteries, the non-peptide OPC-21268 is a partial V 1 receptor agonist with no V 1 receptor antagonist activity, whereas the non-peptide OPC-31260 acts as a V 1 receptor antagonist. Both OPC-21268 and OPC-31260 have V 1 receptor antagonistic activity in vitro in the rat mesenteric resistance arteries. 7. These findings illustrate the complexity of the vasopressin receptor system and highlight the variability in results with peptide or non-peptide vasopressin analogues, between studies in vivo or in vitro , between species and across vascular beds.

1. The effect of atrial natriuretic peptide on osmotically stimulated thirst appreciation and consequent fluid intake was investigated in healthy man. 2. Six seated male subjects were studied on two occasions: synthetic α-human atrial natriuretic peptide (99–126) (2 pmol min −1 kg −1 ) or placebo (saline, 150 mmol/l NaCl) was infused intravenously for 105 min; 30 min after the start of atrial natriuretic peptide/placebo infusion, hypertonic saline (855 mmol/l NaCl) was infused (0.06 ml min −1 kg −1 ) for 60 min. Subjects were then allowed free access to water for the next 2 h; infusion of atrial natriuretic peptide/ placebo continued for the first 15 min of the drinking period. 3. The plasma atrial natriuretic peptide concentration did not alter significantly during infusion of hypertonic saline and placebo; it rose to a steady state of 12.7 ± 1.1 pmol/l (mean ± SEM) during the infusion of atrial natriuretic peptide and hypertonic saline, and remained at this level during the first 15 min of the drinking period. During infusion of hypertonic saline and atrial natriuretic peptide or placebo, similar increases in plasma osmolality ( P < 0.001) and plasma vasopressin concentration ( P < 0.005) occurred. During infusion of hypertonic saline and atrial natriuretic peptide or placebo, thirst increased significantly over the time course of both studies ( P <0.01), but the effect of atrial natriuretic peptide infusion compared with placebo infusion was to significantly decrease thirst at 60 min. 4. Drinking rapidly abolished thirst and vasopressin secretion before changes in plasma osmolality occurred. Subjects drank significantly less water after atrial natriuretic peptide infusion compared with after placebo infusion ( P <0.01). 5. In conclusion, physiological increases in plasma atrial natriuretic peptide concentrations blunt osmotically stimulated thirst appreciation and attenuate subsequent fluid intake in hyperosmolar man.