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BNP (B-type natriuretic peptide) has been reported to be elevated in preclinical states of vascular damage. To elucidate the relationship between plasma BNP and endothelial function, we have investigated the relationship between BNP and endothelial function in a cohort of subjects comprising healthy subjects as well as at-risk subjects with cardiovascular risk factors. To also clarify the relative contribution of different biological pathways to the individual variation in endothelial function, we have examined the relationship between a panel of multiple biomarkers and endothelial function. A total of 70 subjects were studied (mean age, 58.1±4.6 years; 27% had a history of hypertension and 18% had a history of hypercholesterolaemia). Endothelium-dependent vasodilatation was evaluated by the invasive ACH (acetylcholine)-induced forearm vasodilatation technique. A panel of biomarkers of biological pathways was measured: BNP, haemostatic factors PAI-1 (plasminogen-activator inhibitor 1) and tPA (tissue plasminogen activator), inflammatory markers, including cytokines [hs-CRP (high sensitive C-reactive protein), IL (interleukin)-6, IL-8, IL-18, TNFα (tumour necrosis factor α) and MPO (myeloperoxidase] and soluble adhesion molecules [E-selectin and sCD40 (soluble CD40)]. The median BNP level in the study population was 26.9 pg/ml. Multivariate regression analyses show that age, the total cholesterol/HDL (high-density lipoprotein) ratio, glucose and BNP were independent predictors of endothelial function, and BNP remained an independent predictor (P=0.009) in a binary logistic regression analysis using FBF (forearm blood flow) as a dichotomous variable based on the median value. None of the other plasma biomarkers was independently related to ACH-mediated vasodilatation. In a strategy using several biomarkers to relate to endothelial function, plasma BNP was found to be an independent predictor of endothelial function as assessed by endothelium-dependent vasodilatation in response to ACH.

CNP (C-type natriuretic peptide) is a vasodilatory peptide produced by vascular endothelium and the human heart with a short half-life. CNP has been identified within the human kidney; however, few results are available on whether the human kidney is a systemic source of CNP. The aim of the present study was to establish whether CNP is secreted by the human kidney and if synthesis is blunted in CHF (chronic heart failure). A total of 20 male subjects (age, 57+/-2 years; mean+/-S.E.M.) undergoing CHF assessment (n=13) or investigation of paroxysmal supraventricular arrhythmia (normal left ventricular function in sinus rhythm during procedure) (n=7) were recruited. Renal CNP production was determined from concomitant plasma concentrations in the aorta and renal vein. When considering all subjects, a significant step-up in plasma CNP was found from the aorta to renal vein (3.0+/-0.3 compared with 8.3+/-2.4 pg/ml respectively; P=0.0045). The mean increase in CNP was 5.3+/-2.4 pg/ml (range, -0.9 to +45.3 pg/ml). In patients with CHF, the aortic concentration was 3.3+/-0.4 pg/ml compared with a renal vein concentration of 4.3+/-0.6 pg/ml (P=0.11). In those with normal left ventricular function, the respective values were 2.5+/-0.5 and 15.7+/-6.0 pg/ml (P=0.01). In conclusion, CNP is synthesized and secreted into the circulation by the normal human kidney, where it may have paracrine actions. Net renal secretion of CNP appears to be blunted in patients with CHF.

Experimental studies have suggested a role for aldosterone and glucocorticoids in the pathogenesis of endothelial dysfunction. We therefore set out to characterize the acute effects of these hormones on vascular function in vivo in normal humans. A randomized, placebo-controlled, double-blind crossover study was performed on 16 healthy male volunteers (aged 19-29 years), examining the vascular effects of acute intravenous aldosterone infusion (12 pmol.min(-1).kg(-1) for 4 h) and of oral prednisolone (single 50 mg dose). Peripheral arterial vascular function was assessed by bilateral forearm venous occlusion plethysmography using two parallel study protocols. In the first protocol, eight subjects received, successively, acetylcholine, sodium nitroprusside, noradrenaline, angiotensin I and angiotensin II. The remaining eight subjects received, successively, acetylcholine, sodium nitroprusside, verapamil and noradrenaline. Aldosterone attenuated endothelium-dependent vasodilatation to acetylcholine as compared with either prednisolone or placebo (maximum vasodilatation: placebo, 357+/-38%; aldosterone, 257+/-21%; P <0.05). However, background endothelium-independent vasodilatation was not affected by either aldosterone or prednisolone. There were also no significant changes in vasoconstriction induced by angiotensin or noradrenaline following aldosterone or prednisolone treatment compared with placebo. Blood pressure and baseline blood flow did not differ between any of the study phases. Thus acute short-term systemic administration of aldosterone results in endothelial vasodilator dysfunction in normal men, providing evidence for an aldosterone-induced vasculopathy, which may be particularly relevant not only in heart failure but also in hypertensive patients with high aldosterone/renin ratios.

Cigarette smoking is a pernicious risk factor for the pathogenesis of coronary artery disease, and endothelial dysfunction is an important antecedent event in this process. This is important, as cigarette smoke is directly toxic to endothelial cells. Inhibitors of angiotensin-converting enzyme (ACE) have been shown to improve endothelial function in diabetes and hypercholesterolaemia, and are a promising option in smokers. We treated 23 subjects (age 38+/-12 years; mean+/-S.D.) for 8 weeks with 20 mg of lisinopril in a randomized controlled trial. Endothelial function was assessed by measurement of forearm blood flow responses to intra-arterial infusions of endothelial-dependent and -independent vasodilators and an endothelial-dependent vasoconstrictor [acetylcholine, sodium nitroprusside and monomethyl-L-arginine (L-NMMA) respectively] using venous occlusion plethysmography. Lisinopril significantly increased the forearm blood flow response to acetylcholine by 20% [lisinopril, 3.12+/-0.37 (mean+/-S.E.M.); placebo, 2.58+/-0.25; P=0.02, 95% confidence intervals (CI) 0.09, 1.06] (values given are ratios of flow in the infused arm to that in the control arm); there was no effect on the response to sodium nitroprusside (lisinopril, 3.97+/-0.40; placebo, 3.92+/-0.39; P=0.84; 95% CI -0.50, 0.61). The vasoconstrictor response to L-NMMA demonstrated a significant improvement (lisinopril, 0.77+/-0.06; placebo, 0.95+/-0.05; P<0.001; 95% CI -0.09, -0.27). In conclusion, these results indicate that ACE inhibition can improve endothelial function in cigarette smokers. We show that lisinopril improves both receptor-mediated and tonic NO release. The mechanism could be either that lisinopril limits the angiotensin II-induced production of superoxide radicals which would normally inactivate NO, or that lisinopril may increase bradykinin-mediated NO release.

Endothelial function is defective in hypercholesterolaemia, and animal models have suggested that angiotensin-converting enzyme inhibitors may prevent arterial damage. We studied the effect of 6 months treatment with lisinopril on endothelial function in a group of patients with hypercholesterolaemia. Forty patients were studied. Forearm blood flow responses to acetylcholine and sodium nitroprusside were assessed by venous occlusion plethysmography. Subjects were then randomized in a double-blind fashion to receive either lisinopril, 20 mg/day (n=20), or placebo (n=20) for 6 months. Plethysmography was then repeated. Baseline variables between groups were comparable. In the lisinopril group blood pressure fell significantly [systolic: 145+/-4 to 128+/-4 mmHg (P<0.001); diastolic: 84+/-2 to 74+/-2 mmHg (P<0.001)]. An improvement was found in the vasodilatory response (expressed as a ratio of the infused/control arm) to acetylcholine, e.g. 3.33+/-0.3 (pre) versus 4.45+/-0.48 (post) at 30 microg/ml (P<0.03), and also to nitroprusside, e.g. 3.0+/-0.2 (pre) versus 3.86+/-0.3 (post) at 3.2 microg/ml (P<0.01). In the placebo group vasodilatation did not change significantly in response to acetylcholine, and nitroprusside responses were unchanged. The data presented suggest that 6 months of lisinopril therapy have a beneficial effect on arterial function in subjects with hyperlipidaemia. Further work should now investigate whether angiotensin-converting enzyme inhibitors are beneficial in reducing mortality and morbidity in hypercholesterolaemia.

1. Recent animal evidence suggests that aldosterone, like angiotensin II, may possess detrimental autonomic modulating properties. Aldosterone has been shown to impair the baroreflex response in animal models. This study is designed to test the hypothesis that aldosterone directly attenuates the baroreflex in vivo in man.2. Fourteen healthy male volunteers [mean age (S.D.) 25 (9) years] received intravenous d-aldosterone (12 pmol.min-1.kg-1) and 5% dextrose (vehicle) in a double-blind crossover fashion, co-infused with incremental doses of intravenous phenylephrine and sodium nitroprusside. Aldosterone had no significant effect on resting blood pressure, heart rate or baroreflex response to sodium nitroprusside. However, reflex responses to phenylephrine were impaired with aldosterone (P<0.01) while blood pressure responses were unaltered. Baroreflex sensitivity was significantly blunted in the aldosterone group [8.36+/-2.19 versus 10.12+/-2.27 ms/mmHg; P<0. 04].3. This study confirms previous observations from animal models that aldosterone impairs the baroreflex response. High aldosterone levels may contribute to the baroreflex dysfunction in cardiovascular diseases such as hypertension and heart failure.

1. As mineralocorticoid and adrenocorticoid activity are both under the diurnal control of adrenocorticotropic hormone secretion, we aimed to evaluate whether the normal circadian rhythm of cortisol and aldosterone secretion was suppressed by inhaled corticosteroid therapy.2.Ten normotensive patients with mild-moderate asthma, mean age 24.0 (S.D. 9.8) years and mean arterial pressure 90.7 (9.8) mmHg, were studied in a double-blind, randomized crossover design comparing placebo with fluticasone propionate, 1000 microgram administered twice daily at 08:00 h and 20:00 h. After 5 days of repeated dosing at steady state, measurements were made of plasma cortisol and aldosterone at midnight and 08:00 h.3. With placebo there was a significant (P<0.05) difference between cortisol values at 08:00 h (588.6+/-83.8 nmol/l) and midnight (109.6+/-35.0 nmol/l), whereas after treatment with fluticasone propionate there was no significant difference between levels at 08:00 h (143.3+/-57.4 nmol/l) and midnight (64.3+/-22.3 nmol/l). For cortisol at 08:00 h there was also a significant (P<0.05) difference between placebo and fluticasone propionate. The same pattern was observed for aldosterone. Plasma aldosterone levels at 08:00 h after treatment with placebo (129.6+/-30.9 nmol/l) were significantly different (P<0. 05) to those seen at midnight (40.4+/-6.2 nmol/l). After treatment with fluticasone propionate, there was no significant difference between levels at midnight (55.4+/-11.7 nmol/l) and 08:00 h (64. 8+/-12.7 nmol/l).4. These results show that inhaled corticosteroid therapy abolishes the circadian rhythm of aldosterone and cortisol secretion. This may have possible implications for patients taking inhaled corticosteroids in terms of the beneficial cardiac effects of suppressing early morning aldosterone.

1. Recent evidence shows that skeletal muscle blood flow is an important determinant of insulin sensitivity and that insulin-mediated vasodilatation is nitric oxide dependent. These results have given rise to the hypothesis that endothelial nitric oxide inhibition may decrease insulin sensitivity in humans. 2. We examined this hypothesis directly by evaluating the effects of systemic nitric oxide synthase inhibition with NG-monomethyl L-arginine (3 mg h-1 kg-1) on whole-body glucose uptake (euglycaemic hyperinsulinaemic clamp) and calf blood flow (bilateral calf venous occlusion plethysmography) in 16 healthy male subjects in a randomized, double-blind, placebo-controlled, crossover study. 3. NG-Monomethyl L-arginine infusion was associated with a pressor effect (119/61 +/- 2/2 compared with 114/58 +/- 2/2 mmHg for placebo; P < 0.001), and a negative chronotropic response (57 +/- 2 compared with 62 +/- 2 beats/min for placebo; P < 0.001). The glucose infusion rate was significantly increased after infusion of NG-monomethyl L-arginine (8.9 +/- 0.9 compared with 7.9 +/- 0.8 mg min-1 kg-1 for placebo; P = 0.002). Whole-body glucose uptake increased during the clamp, with values of 9.4 +/- 0.7 and 10.9 +/- 0.8 mg min-1 kg-1 for placebo and NG-monomethyl L-arginine respectively (P = 0.036; 95% confidence interval 0.2,2.8). NG-Monomethyl L-arginine was associated with increased calf blood flow by comparison with placebo (P < 0.05, area under curve). 4. These data show for the first time that systemic inhibition of nitric oxide synthesis increases rather than decreases whole-body glucose uptake. We suggest that the higher skeletal muscle blood flow seen after NG-monomethyl L-arginine may explain the observed increase in whole-body glucose uptake.

1. Atrial natriuretic peptide and brain natriuretic peptide have similar vasodilator and natriuretic properties, although little information is available regarding their relative effects as antagonists of the renin-angiotensin-aldosterone system. We have therefore compared how atrial natriuretic peptide and brain natriuretic peptide affect the systemic pressor and aldosterone responses to angiotensin II in eight male subjects. 2. Each subject was studied on three separate occasions, when they received a 60-min infusion of placebo, atrial natriuretic peptide (10 pmol min-1 kg-1) or brain natriuretic peptide (10 pmol min-1 kg-1), with a concomitant infusion of angiotensin II (6 ng min-1 kg-1) given for the final 30 min of the infusion period. The change in haemodynamic parameters and plasma aldosterone induced by angiotensin II was measured. Plasma concentrations of atrial natriuretic peptide (182 +/- 23 pmol/l) and brain natriuretic peptide (193 +/- 25 pmol/l) achieved at steady-state during the infusion on each study day were not significantly different. 3. Increases in mean arterial pressure in response to angiotensin II were significantly lowered by concomitant infusion of atrial natriuretic peptide (21.0 +/- 1.7 mmHg) and brain natriuretic peptide (20.1 +/- 1.9 mmHg) compared with placebo (29.0 +/- 4.1 mmHg). There were similar effects on systolic and diastolic blood pressure. Cardiac output was decreased on each study day to the same extent y angiotensin II infusion. Total systemic vascular resistance showed a non-significant trend towards an attenuated response to angiotensin II when atrial natriuretic peptide or brain natriuretic peptide was infused concomitantly in comparison with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The renal effects of incremental doses of intravenously infused noradrenaline were evaluated in normal subjects during two different water loads, 5 ml/kg (n = 6) and 20 ml/kg (n = 9), producing conditions of euhydration and overhydration, respectively. 2. Noradrenaline infusion rates ranged from 0.015 to 0.075 microgram min-1 kg-1. In the euhydrated subjects, noradrenaline caused a dose-dependent fall in urinary sodium excretion and an increase in urinary flow rate. During overhydration similar doses of noradrenaline caused a fall in urinary sodium excretion but a decrease in urinary flow rate. 3. Although there was no detectable change in glomerular filtration rate, a dose-dependent fall in effective renal plasma flow was observed in both hydration states during noradrenaline infusion. 4. Noradrenaline infusion was associated with a dose-dependent increase in proximal tubular sodium reabsorption as assessed by the lithium clearance method. Fractional reabsorption of sodium by the distal nephron was, however, unchanged by noradrenaline in both hydration states. 5. Plasma vasopressin concentration was unchanged by noradrenaline in euhydrated subjects. The renin-angiotensin-aldosterone axis was stimulated by noradrenaline in both euhydrated and overhydrated subjects. 6. Thus we conclude that plasma circulating noradrenaline has a dose-dependent antinatriuretic effect in man. The antinatriuretic effect of noradrenaline is mediated mainly at the proximal tubule in man. We have also shown that during overhydration, noradrenaline decreased urinary flow rate. In contrast, in euhydrated subjects, noradrenaline increased urinary flow rate with no accompanying changes in plasma vasopressin concentration, which suggests a direct effect of noradrenaline on the renal tubular permeability to water.

1. Animal studies have shown that angiotensin II has a biphasic effect on urinary sodium excretion. To examine whether this is also true in man, we studied seven salt-replete male subjects in a single-blind placebo-controlled manner. 2. While undergoing maximum diuresis, subjects were infused with 0, 1, 2, 5 or 10 ng of angiotensin II min-1 kg-1 over 80 min. Subjects were studied while seated, and stood every 20 min for urine collection. 3. Angiotensin II produced a dose-dependent antidiuretic effect. The urine flow rate, in ml/min expressed as the change from baseline with increasing dose of angiotensin, was: +3.4 +/- 1.77, -1.26 +/- 0.49 (P < 0.05), -2.75 +/- 1.23 (P < 0.05), -4.21 +/- 0.82 (P < 0.05) and -6.51 +/- 1.07 (P < 0.01). 4. In contrast, the effect of angiotensin II on sodium excretion showed a flat dose-response curve beyond 5 ng min-1 kg-1. The urinary sodium excretion, in mumol/min expressed as the change from baseline with increasing dose of angiotensin, was: 9.5 +/- 21.2, -18.9 +/- 29.6, -37.0 +/- 11.6 (P < 0.05), -67.7 +/- 19.6 (P < 0.01) and -63.8 +/- 14.3 (P < 0.01). 5. The fractional distal reabsorption of sodium, determined by using the lithium clearance technique, showed a rise with all doses of angiotensin II used and reached statistical significance with the top two doses. 6. Unlike antidiuresis, antinatriuresis after graded doses of angiotensin II in human subjects showed a flat dose-response curve beyond 5 ng min-1 kg-1. Pressor doses of angiotensin II also have a significant effect on the distal tubule in promoting sodium reabsorption.

1. Studies in vitro have recently shown that both atrial natriuretic peptide and brain natriuretic peptide have pulmonary vasorelaxant activity. The purpose of the present study was to evaluate for the first time whether plasma levels of brain natriuretic peptide are elevated in chronic obstructive pulmonary disease. Plasma levels of brain natriuretic peptide and atrial natriuretic peptide were therefore measured in 12 patients admitted with acute hypoxaemic chronic obstructive pulmonary disease [arterial partial pressure of O2, 6.2 +/- 0.4 kPa; arterial partial pressure of CO2, 6.9 +/- 0.1 kPa; forced expiratory volume in 1 s, 0.6 +/- 0.07 litre (27 +/- 3% of predicted)]. All but three patients had oedema on admission. 2. Plasma levels of both brain natriuretic peptide and atrial natriuretic peptide were elevated in patients with chronic obstructive pulmonary disease (31.4 +/- 4.1 pmol/l and 45.0 +/- 8.1 pmol/l, respectively) compared with healthy control subjects (1.7 +/- 0.8 pmol/l and 8.0 +/- 3.5 pmol/l, respectively). Thus, plasma levels of brain natriuretic peptide and atrial natriuretic peptide in patients with chronic obstructive pulmonary disease were increased by 18.5- and 5.6-fold respectively compared with healthy control subjects. 3. There was a significant inverse correlation between the plasma level of brain natriuretic peptide and the arterial partial pressure of O2 (r = -0.65, r2 = 0.42, P = 0.03), but not between the plasma atrial natriuretic peptide level and the arterial partial pressure of O2 (r2 = 0.07, not significant). The arterial partial pressure of CO2 did not correlate with the plasma level of either brain natriuretic peptide or atrial natriuretic peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The aim of this study was to examine the effect of captopril, an angiotensin-converting enzyme inhibitor, on plasma levels of human brain natriuretic peptide-like immunoreactivity (hBNP-li) in patients with congestive heart failure. 2. Six male patients (aged 52-74 years) with mild to moderate congestive heart failure were studied on two occasions in the semi-recumbent position. After a 30 min rest, patients were randomized to receive oral tablets of either captopril (6.25 mg followed by 25 mg 2 h later) or placebo in a single-blind manner. Plasma hBNP-li, atrial natriuretic peptide-like immunoreactivity (ANP-li) and angiotensin II-like immunoreactivity (ANG II-li) levels and blood pressure were measured. 3. Baseline plasma hBNP-li and ANP-li levels in these patients with mild to moderate congestive heart failure were 13.5 +/- 3.2 pmol/l and 50.9 +/- 11.8 pmol/l, respectively. In 11 healthy male subjects aged 20-23 years, the peripheral plasma hBNP-li and ANP-li levels were 1.3 +/- 0.2 pmol/l and 5.6 +/- 1.7 pmol/l, respectively. In all patients, captopril decreased the plasma ANG II-li level (from 24.3 +/- 8.1 to 6.6 +/- 3.2 pmol/l, P < 0.05) and mean arterial blood pressure (from 92 +/- 3 to 80 +/- 3 mmHg, P < 0.05). Compared with placebo, captopril treatment was associated with significant reductions in plasma hBNP-li (from 14.3 +/- 3.0 to 12.8 +/- 2.1 pmol/l, P < 0.05) and in plasma ANP-li (from 53.9 +/- 1.11 to 36.8 +/- 7.6 pmol/l, P < 0.05) levels.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Brain natriuretic peptide is a new natriuretic hormone with striking similarity to atrial natriuretic peptide, but there are no previous data concerning its clearance in man. Two pathways of clearance for atrial natriuretic peptide are recognized: degradation by neutral endopeptidase and binding to atrial natriuretic peptide clearance receptors. We have examined the effect of candoxatril, an inhibitor of neutral endopeptidase (dose range 10-200 mg), and the effect of an infusion of a pharmacological dose [45 micrograms (90 micrograms in two patients)] of synthetic human atrial natriuretic peptide on plasma human brain natriuretic peptide-like immunoreactivity levels in seven patients with mild to moderate chronic heart failure. 2. Plasma human brain natriuretic peptide-like immunoreactivity levels were elevated in all patients (mean +/- SEM 22.0 +/- 6.2 pmol/l) compared with healthy control subjects (1.3 +/- 0.2 pmol/l, n = 11). 3. In all patients, candoxatril increased both plasma atrial natriuretic peptide (P less than 0.05) and plasma human brain natriuretic peptide-like immunoreactivity (P less than 0.05) levels. 4. By contrast, an exogenous infusion of atrial natriuretic peptide had no effect on plasma human brain natriuretic peptide-like immunoreactivity levels despite increasing the plasma atrial natriuretic peptide concentration to 424 +/- 74 pmol/l, which is a level of atrial natriuretic peptide which would have 'swamped' all atrial natriuretic peptide clearance receptors. 5. We have therefore shown that plasma human brain natriuretic peptide-like immunoreactivity levels in chronic heart failure are increased by a neutral endopeptidase inhibitor, but are unchanged by an exogenous infusion of atrial natriuretic peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The response of systemic and regional haemodynamic indices to increasing infusion rates of angiotensin II (1, 3 or 10 ng min-1 kg-1) or placebo [5% (w/v) D-glucose] was studied in eight normal male subjects. 2. As compared with placebo, angiotensin II infusion caused an incremental rise in the serum angiotensin II level [14.5 +/- 7.7 (placebo) to 187.2 +/- 36.1 (10 ng of angiotensin II min-1 kg-1) pmol/l; mean +/- 95% confidence interval] associated with a stepwise increase in total peripheral resistance [880 +/- 42 (placebo) to 1284 +/- 58 (10 ng of angiotensin II min-1 kg-1) dyn s cm-5] and a progressive reduction in cardiac output [8.3 +/- 0.4 (placebo) to 7.0 +/- 0.4 (10 ng of angiotensin II min-1 kg-1) litres/min]. 3. A stepwise fall in renal blood flow was observed with increasing angiotensin II infusion rate [1302 +/- 65 (placebo) to 913 +/- 64 (10 ng of angiotensin II min-1 kg-1) ml/min]. In contrast, calf blood flow was unaffected by 1 ng or 3 ng of angiotensin II min-1 kg-1 and was significantly increased by 10 ng of angiotensin II min-1 kg-1 (P less than 0.01). 4. Calf venous capacitance was uninfluenced by 1 ng of angiotensin II min-1 kg-1, but was significantly increased by both 3 ng (P less than 0.005) and 10 ng (P less than 0.001) of angiotensin II min-1 kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Plasma human brain natriuretic peptide-like immunoreactivity (hBNP-li) was measured in ten patients with chronic renal failure before and after 4 h of haemodialysis. 2. Plasma hBNP-li was elevated in all patients before dialysis (mean +/- SEM 21.0 +/- 3.8 pmol/l) compared with healthy control subjects (1.3 +/- 0.2 pmol/l, n = 11), but showed considerable inter-patient variability. Before dialysis plasma hBNP-li bore no relationship to the serum creatinine level or to the mean blood pressure. 3. Plasma hBNP-li fell significantly (P = 0.04) during 4 h of haemodialysis. The fall in plasma hBNP-li correlated significantly with the degree of postural blood pressure drop (r2 = 0.44, P = 0.05) and with the fall in body weight (r2 = 0.64, P less than 0.01) after haemodialysis. In all patients, plasma hBNP-li at the end of treatment remained above that in healthy subjects. 4. There was no significant correlation between the fall in plasma hBNP-li and the fall in serum creatinine level, and between the fall in plasma hBNP-li and the fall in supine systolic or diastolic blood pressure, during haemodialysis. 5. We have shown that plasma hBNP-li is elevated in patients with chronic renal failure and is decreased during haemodialysis. The fact that the plasma hBNP-li was not reduced to normal by haemodialysis despite restoration to normovolaemia gives tentative support to the view that, in addition to hypervolaemia, another factor may also be responsible for the elevated plasma hBNP-li seen in these patients.

1. In animal studies, angiotensin II facilitates adrenergic neurotransmission by both pre- and post-synaptic mechanisms. We have investigated whether this interaction occurs in forearm resistance vessels in man. 2. The effect of arterial infusion of angiotensin II (320 fmol/min) on sympathetic vasoconstriction produced by lower-body negative pressure (15 mmHg) was studied in six subjects, and that on the response to exogenous noradrenaline (37.5-150 pmol/min) was studied in a further eight subjects. Forearm blood flow was measured by strain-gauge plethysmography. 3. The dose of angiotensin II was chosen to produce no alteration in resting blood flow, and those of noradrenaline were selected to provide a reduction in blood flow equivalent to that produced by lower-body negative pressure. 4. Lower-body negative pressure produced no change in heart rate or diastolic blood pressure, but caused an initial 5 mmHg fall in systolic blood pressure (P less than 0.01). Blood flow was reduced by 21 +/- 6% in both forearms by lower-body negative pressure during saline infusion. During angiotensin II infusion, there was a marked difference in the response to lower-body negative pressure, with blood flow being reduced by 40 +/- 7% in the infused arm, but only by 21 +/- 4% in the control arm (P less than 0.05). Angiotensin II infusion had no effect on resting blood flow or the responses to noradrenaline. 5. We conclude that angiotensin II augments sympathetic vasoconstriction in forearm resistance vessels in man at a concentration that has no direct effect on blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Twelve normal subjects were given 5 days' treatment with (a) placebo; (b) 5 mg of bendrofluazide; (c) 5 mg of bendrofluazide plus 24 mmol of potassium; (d) 5 mg of bendrofluazide plus 24 mmol of magnesium; (e) 5 mg of bendrofluazide plus 24 mmol of potassium plus 24 mmol of magnesium; (f) 5 mg of bendrofluazide plus 50 mg of triamterene. 2. After each treatment period, subjects were given two doses of inhaled salbutamol (each of 1 mg), and measurements were made 25 min after each dose. 3. Treatment with bendrofluazide plus salbutamol produced a lower absolute level of plasma potassium than salbutamol alone, although the addition of potassium, magnesium or triamterene did not attenuate this effect. Plasma magnesium was unchanged by salbutamol. 4. Salbutamol was associated with significant electrocardiographic effects, including T-wave flattening, Q-Tc interval prolongation and, in some subjects, U-waves and S-T segment depression. 5. Prior treatment with bendrofluazide potentiated the electrocardiographic effects of salbutamol. Supplementation with potassium and magnesium had no effect on electrocardiographic changes, and the addition of triamterene to bendrofluazide only attenuated electrocardiographic responses in some subjects.

1. Angiotensin II (ANG II; 1 ng min-1 kg-1) or 5% (w/v) D-glucose (placebo) was infused in six normal male volunteers, pretreated with 500 mg of lithium carbonate, who were undergoing maximal water diuresis. 2. This dose of ANG II caused a circulating increment within the physiological range (27 +/- 4 to 48 +/- 9 pmol/l). 3. Compared with placebo, ANG II caused a significant fall in urinary sodium excretion (113 +/- 13 to 82 +/- 10 mumol/min). This antinatriuretic effect occurred without a fall in creatinine clearance (107 +/- 3 versus 113 +/- 3 ml/min). 4. ANG II caused a significant fall in fractional lithium clearance (28 +/- 2 to 23 +/- 2%). This may indicate a proximal tubular effect of ANG II. 5. ANG II also reduced fractional distal delivery [(sodium clearance plus free water clearance) divided by creatinine clearance], another measure of proximal tubular outflow. A parallel change in these two separate markers of proximal function supports an action of ANG II at this nephron segment. 6. Furthermore, the antinatriuretic effect of ANG II was unlikely to be due to stimulation of aldosterone secretion because (a) the fall in sodium excretion was temporally dissociated from the rise in aldosterone secretion, (b) potassium excretion also tended to fall during ANG II infusion and (c) aldosterone has a distal nephron effect, while, in this study, proximal nephron fractional reabsorption of sodium increased and distal nephron fractional reabsorption of sodium was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

We have investigated the interaction between the recently discovered natriuretic factor alpha human atrial natriuretic peptide (alpha h-ANP) and the renin-angiotensin-aldosterone system in man. Angiotensin II infused with placebo produced a significant rise of plasma aldosterone concentration (mean +/- SEM increment 352 +/- 23 pmol/l, n = 7, P less than 0.001). The infusion of alpha h-ANP together with angiotensin II largely abolished the aldosterone response (P less than 0.001). Diastolic blood pressure rose in response to the infusion of angiotensin II with placebo (mean increment 21.0 +/- 0.9 mmHg, P less than 0.001). Systolic blood pressure increased to a lesser degree (mean increment 12.5 +/- 0.7 mmHg, P less than 0.001). The infusion of alpha h-ANP together with angiotensin II significantly blunted the diastolic pressor response (P less than 0.01). This ability of alpha h-ANP to blunt the pressor effect of angiotensin II may be important in the control of systemic blood pressure. The inhibition of angiotensin II-stimulated aldosterone release demonstrates that alpha h-ANP may not only be a circulating natriuretic factor in its own right but that it may also act as a modulator of a related endocrine system.

Adrenaline was infused intravenously in nine normal volunteers to plasma concentrations similar to those found after myocardial infarction. This study was undertaken on three occasions after 5 days' treatment with placebo or the beta-adrenoceptor antagonists, atenolol or timolol. Adrenaline increased the systolic pressure by 11 mmHg, decreased the diastolic pressure by 14 mmHg, and increased the heart rate by 7 beats/min. These changes were prevented by atenolol. However, after timolol the diastolic pressure rose (+19 mmHg) and heart rate fell (-8 beats/min). Adrenaline caused the corrected QT interval (QTc) to lengthen (0.36 +/- 0.02 s to 0.41 +/- 0.06 s). No significant changes were found in the QTc when subjects were pretreated with atenolol or timolol. The serum potassium fell from 4.06 to 3.22 mmol/l after adrenaline. Serum potassium fell to a lesser extent to 3.67 mmol/l after atenolol and actually increased to 4.25 mmol/l after timolol. Adrenaline-mediated hypokalaemia appears to result from the stimulation of a beta 2-adrenoceptor linked to membrane Na+/K+-ATPase causing potassium influx.

In addition to calcitonin and katacalcin, it is now known that the human calcitonin gene encodes a novel peptide called calcitonin gene related peptide (CGRP). In experimental animals, CGRP produces vasodilatation and complex changes in plasma calcium. We have now assessed its biological activity in man by infusing human CGRP (hCGRP) into six normal volunteers. hCGRP (545 pmol/min) caused the diastolic pressure to fall from 64 +/- 5 to 55 +/- 7 mmHg (P less than 0.05), the heart rate to increase from 61 +/- 7 to 87 +/- 5 beats/min (P less than 0.05) and the skin temperature to increase from 33.7 +/- 0.9 to 34.9 +/- 0.5 degrees C. Plasma noradrenaline increased from 481 +/- 126 to 835 +/- 65 pg/ml (P less than 0.05) and plasma adrenaline from 57 +/- 17 to 82 +/- 12 pg/ml (P less than 0.05). There were no significant changes in the albumin-corrected plasma calcium. hCGRP is thus a potent endogenous vasodilator in man and is in fact more potent than any other known vasodilator. Together with the observations that CGRP circulates in normal subjects at relatively high concentration (approximately 25 pmol/l) and that CGRP is present in perivascular nerves, this study suggests a possible role for CGRP in controlling peripheral vascular tone in man.

1. The game of squash has recently been associated with a high incidence of ventricular arrhythmias and sudden death. To investigate this further, plasma catecholamines and potassium (K+) were monitored during a game of squash in six normal volunteers. 2. No cardiac arrhythmias were seen in this study despite the subjects reaching maximum heart rates of 181 +/- 5 beats/min (mean +/- SEM). 3. During exercise, plasma K+ rose from 3.82 +/- 0.16 to 4.29 +/- 0.2 mmol/l, but after 90 s rest this fell to 3.68 +/- 0.28 mmol/l and after 180 s to 3.44 +/- 0.17 mmol/l. This rapid K+ shift could not be accounted for by generalized changes in venous acid-base status or by changes in venous plasma catecholamines. Although pretreatment with a beta 2-antagonist caused the overall plasma K+ levels to be higher, it had no significant effect on the fall in plasma K+ after exercise. 4. Such rapid K+ shifts after exercise might contribute to arrhythmogenesis in susceptible individuals. The precise mechanism of the fall in K+ after exercise remains undetermined, but it seems not to involve catecholamines stimulating beta 2-adrenoceptors and is more likely to be due to increased skeletal muscle blood flow and/or intracellular acidosis.

Six healthy volunteers received a 60 min infusion of guanfacine (alpha 2-agonist) on two occasions, preceded by either idazoxan (alpha 2-antagonist) or vehicle. Idazoxan elevated blood pressure by 8/7 mmHg, but there was no change on either day during guanfacine infusion. Guanfacine reduced plasma noradrenaline by approximately 30%, and this was not antagonized by idazoxan. By contrast, the 30-fold increase in plasma growth hormone caused by guanfacine was almost completely blocked by idazoxan. Guanfacine caused a two- to three-fold increase in plasma glucagon and a similar reduction in plasma insulin. Only the latter was antagonized by idazoxan. No consistent changes in plasma ACTH were observed after either idazoxan or guanfacine. Idazoxan itself elevated plasma noradrenaline up to twice baseline values, but did not affect the other metabolic measurements. alpha 2-Adrenoceptor stimulation plays a minor role in control of hormone release but has a greater physiological role in regulating release of the neurotransmitter, noradrenaline.

1. Atrial natriuretic peptide (ANP) has previously been shown to inhibit the renin-angiotensin-aldosterone system (RAAS) at several different levels. We have now investigated a further non-endocrine, renal interaction between ANP and the RAAS. 2. The effects of ANP and angiotensin II (ANG II) alone, and in combination, on urinary electrolyte and water excretion were studied in eight normal male subjects undergoing maximal water diuresis. 3. ANP caused a significant increase in urine flow and sodium excretion. ANG II alone was antidiuretic, antinatriuretic and antikaliuretic. When ANP was given against a background infusion of ANG II, urinary flow rate and electrolyte excretion increased from a new lower level to reach a value intermediate between that found with ANG II alone and ANP alone. 4. It is concluded that the renal effects of ANP are modified in the presence of simultaneously elevated levels of ANG II and that net water and electrolyte excretion reflect the sum of the opposing influences of each peptide. While this interplay may be non-specific, it is possible that ANP may exert some of its actions by specifically inhibiting the intrarenal effects of ANG II.