Alpha hANP Research Articles

Effects of alpha-human natriuretic peptide on renal hemodynamics and diuresis in dogs and perfused rat kidneys.

Effects of alpha-human atrial natriuretic polypeptide (alpha-hANP) on renal function were studied in anesthetized dogs and isolated perfused rat kidneys. Two doses of alpha-hANP were used to determine whether renal hemodynamics or tubular reabsorption is tha major factor in the diuretic action of alpha hANP. The excretion rates of sodium (Na) and inorganic phosphate (PO4) were evaluated to determine the site of diuretic action in the renal tubule. In dogs that received the smaller dose of alpha-hANP (5 ng.kg-1.min-1) infused into the renal arteries without changes in systemic or renal hemodynamics, urine volume (UV) and urinary Na excretion (UNaV) increased significantly. Fractional excretion of Na (FENa) was increased, while fractional excretion of PO4 (FEpo4) was unchanged, following the infusion of alpha-hANP. The calculated fractional Na reabsorption in the distal tubule (DTRNa) during the infusion of alpha-hANP was significantly suppressed. In dogs that received the a larger dose of alpha-hANP (50 ng.kg-1.min-1), the glomerular filtration rate (GFR), UV, and FENa were increased and DTRNa was decreased. In isolated rat kidneys perfused at a constant pressure, a lower concentration of alpha-hANP (0.5 ng.ml-1) in the perfusate caused diuresis and increased Na and PO4 excretion without any renal hemodynamic alterations. A higher concentration of alpha-hANP (5 ng.ml-1) increased GFR, Na and PO4 excretion. Since PO4 reabsorption is believed to occur primarily in the renal proximal tubule, these findings suggest that the diuretic action of alpha-hANP in smaller doses in induced by direct action on renal distal nephron.(ABSTRACT TRUNCATED AT 250 WORDS)

The significance of atrial natriuretic polypeptide in the cause of essential hypertension

The study was undertaken to clarify the role of atrial natriuretic polypeptide (ANP) in essential hypertension (EH). Plasma levels of alpha-human ANP (alpha hANP) were measured in 13 normal subjects, 25 patients with EH, 5 patients with primary aldosteronism (PA), 3 patients with renovascular hypertension (RVH) and 3 patients with pheochromocytoma (PC). Plasma level of alpha hANP (normal: 38.1 +/- 20.5pg/ml) was high in all hypertensive subjects. Synthetic alpha hANP was intravenously administrated to these subjects as follows: first a dose of 0.01 microgram/kg/min for 30 minutes, second a dose of 0.03 microgram/kg/min for 30 minutes, and then in normal subjects and EH 0.03 microgram/kg/min with a dose of 6.5 micrograms/kg/min of metoclopramide (MC) for 30 minutes. After the infusion of 0.01 microgram/kg/min alpha hANP, arterial blood pressure was significantly depressed in EH, RVH and PA, but not in PC. Marked diuretic and natriuretic responses were observed with increase in creatinine clearance and fractional sodium excretion in EH, RVH and PA, but not in PC. Sodium clearance/lithium clearance was slightly increased after infusion of 0.03 microgram/kg/min of alpha hANP in hypertensive subjects. Plasma renin activity did not change in low and normal renin EH and PA after infusion of either dose of alpha hANP, but was suppressed after 0.03 microgram/kg/min of alpha hANP in normal subjects and high renin EH, RVH and PC. Plasma aldosterone concentration was suppressed after either dose of alpha hANP in normal subjects and in EH, RVH and PC, but not in PA. Plasma cGMP concentration and urinary cGMP excretion were decreased after either dose of alpha hANP in both normal and hypertensive subjects. Furthermore, the decrease of PAC by alpha hANP was normalized by MC in normal subjects and EH. The rise in plasma cGMP by alpha hANP was suppressed by MC in both normal subjects and EH, but no changes were observed in arterial blood pressure and natriuretic response. These results suggest that alpha hANP secretion increases with elevation of blood pressure in EH, improving increase of circulatory blood volume, and alpha hANP may play a role in elevating blood pressure in EH. Moreover, it is considered that ANP increases sodium and water excretion through its effect on both renal glomeruli and distal tubules in EH. Hypotensive and natriuretic effects of ANP in EH may be concerned with dopaminergic activity which are probably related to the production of cGMP in the vascular wall and inhibition of the excretion of aldosterone in the adrenal cortex.

The hydrolysis of brain and atrial natriuretic peptides by porcine choroid plexus is attributable to endopeptidase-24.11

The hydrolysis of the porcine 26-residue brain natriuretic peptide (BNP-26) and its counterpart human 28-residue atrial natriuretic peptide (alpha-hANP) by pig membrane preparations and purified membrane peptidases was studied. When the two peptides were incubated with choroid plexus membranes, the products being analysed by h.p.l.c., alpha-hANP was degraded twice as fast as BNP. The h.p.l.c. profiles of alpha-hANP hydrolysis, in short incubations with choroid plexus membranes, yielded alpha hANP' as the main product, this having been previously shown to be the result of hydrolysis at the Cys7-Phe8 bond. In short incubations this cleavage was inhibited 84% by 1 microM-phosphoramidon, a specific inhibitor of endopeptidase-24.11. BNP-26 was hydrolysed by choroid plexus membranes, kidney microvillar membranes and purified endopeptidase-24.11 in a manner that yielded identical h.p.l.c. profiles. In the presence of phosphoramidon, hydrolysis by the choroid plexus membranes was 94% inhibited. Captopril had no effect and, indeed, no hydrolysis of BNP-26 by peptidyl dipeptidase A (angiotensin-converting enzyme) was observed even after prolonged incubation with the purified enzyme. The stepwise hydrolysis of BNP-26 by endopeptidase-24.11 was investigated by sequencing the peptides produced during incubation. The initial product resulted from hydrolysis at Ser14-Leu15, thereby opening the ring. This product (BNP') was short-lived; further degradation involved hydrolysis at Ile12-Gly13, Arg8-Leu9, Gly17-Leu18, Val22-Leu23, Arg11-Ile12 and Cys4-Phe5. Thus endopeptidase-24.11 is the principal enzyme in renal microvillar and choroid plexus membranes hydrolysing BNP-26 and alpha-hANP.

Atrial natriuretic peptide infusion causes vasoconstriction after autonomic blockade in conscious dogs

Many studies have shown that atrial natriuretic peptide (ANP) reduces mean arterial pressure (MAP) in conscious animals by lowering cardiac output (CO) with no change or even increased total peripheral resistance (TPR). Because ANP is thought to be a vasodilator, the lack of fall in TPR in conscious animals is generally considered to be due to autonomic reflex increases in vascular resistance. In the present study in conscious, trained, chronically instrumented dogs (n = 7), we measured hemodynamic and renal excretory responses to 30-min infusions of alpha-human ANP (alpha hANP; 25, 50, and 100 ng.kg-1.min-1) in the presence and absence of autonomic nervous system blockade using the ganglion blocking agent pentolinium. In the absence of blockade, MAP and CO fell, whereas TPR rose with alpha hANP infusions, but these changes did not reach significance. There were significant increases in renal vascular resistance (RVR; 16-25%) and mesenteric vascular resistance (MVR; 14-40%). During autonomic nervous system blockade, alpha hANP caused dose-related reductions in MAP (7-12%), due to falls in CO (13-34%). Remarkably, the absence of autonomic reflex responses exposed substantial dose-related increases in TPR (5-33%). Autonomic blockade did not alter the ANP-induced increases in MVR but did abolish the rises in RVR. In summary, ANP caused vasoconstriction in mesenteric vasculature and substantial vasoconstriction in other nonrenal areas, independent of autonomic reflexes.

Effects of brain natriuretic peptide on hemodynamics and renal function in dogs.

A new natriuretic peptide has been found in the porcine brain and termed brain natriuretic peptide (BNP). To examine the effects of BNP on the cardiovascular system and kidney as compared with alpha-hANP (ANP), BNP, and ANP (33, 167, 667 pmol/kg) were intravenously administered to anesthetized dogs. BNP dose-dependently decreased arterial pressure and left atrial pressure and dose-dependently increased heart rate, cardiac output, renal blood flow, urine volume, and sodium excretion. These effects were not significantly different from the effects of respective doses of ANP. To eliminate the possibility that these results were confounded by opposing actions of the baroreflex system, we performed additional experiments following sinoaortic denervation and vagotomy. These results also demonstrated no differences between the effects of BNP and ANP on the measured variables. Finally, we determined that the pharmacokinetics of exogenously injected BNP and ANP are indistinguishable. These findings lead to the possibility that BNP physiologically works in the body in the same manner as ANP.

Amelioration of Postischaemic Acute Renal Failure in Conscious Dogs by Human Atrial Natriuretic Peptide

We studied the effect of human ANP (alpha-hANP)-99-126 on the course of postischaemic acute renal failure in unilaterally nephrectomised, conscious dogs subjected to 120 min of renal ischaemia. In contrast to a control group A (n = 7), the investigational group B (n = 9) received an intra-aortic bolus injection of 100 micrograms/kg alpha-hANP and an additional continuous infusion of 0.3 micrograms/kg per min x 180 min immediately after ischaemia. On days 1 and 2 after ischaemia, only the bolus injection was repeated. Administration of hANP resulted in a marked restoration of GFR (29 +/- 2 vs 18 +/- 4 ml/min, P less than or equal to 0.01), diuresis (0.8 +/- 0.1 vs 0.5 +/- 0.1 ml/min, P less than or equal to 0.05), and natriuresis (44 +/- 7 vs 25 +/- 4 mumol/min, P less than or equal to 0.05) on the first postischaemic day, which was mirrored by a reduction in nitrogen retention (Purea: 8 +/- 1 vs 12 +/- 2 mmol/l P less than or equal to 0.05, Pcrea: 137 +/- 20 vs 204 +/- 37 mumol/l). Renal perfusion, however, was only slightly improved on day 1 after ischaemia (198 +/- 20 vs 163 +/- 27 ml/min, N.S.). Our data clearly demonstrate that repeated bolus applications of hANP ameliorate postischaemic acute renal failure in conscious dogs. We assume that the observed beneficial effect on GFR might be the consequence of an increase in glomerular capillary pressure rather than an improvement of renal perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of Plasma α Human Atrial Natriuretic Polypeptide using

To clarify the molecular nature and dynamics of circulating alpha human atrial natriuretic polypeptide (alpha hANP) in chronic renal disease, the plasma concentrations of alpha hANP were determined by radioimmunoassays using two distinct monoclonal antibodies (MoAbs). One MoAb (10B1) recognized N-terminus of alpha hANP, while the other (C351) recognized the ring structure. The preliminary studies revealed a close correlation (r = 0.97, p less than 0.0001) between plasma alpha hANP measured with 10B1 and C351 MoAbs, supporting the theory that the main circulating form is alpha hANP(1-28). Therefore, the more sensitive radioimmunoassay using MoAb (C351) was used in the present studies. The plasma alpha hANP was 3.8 +/- 1.7 (mean +/- SD) in healthy subjects, 2.7 +/- 1.4 fmol/ml in patients with chronic glomerulonephritis without renal failure, 16.2 +/- 16.8 fmol/ml in patients with chronic renal failure, and 24.3 +/- 10.5 fmol/ml in patients under maintenance hemodialysis. Thus, the elevation of plasma alpha hANP was related to the stages of renal damage. Although the plasma alpha hANP in 18 patients under maintenance hemodialysis declined significantly (p less than 0.01) after hemodialysis, their levels (17.9 +/- 9.0 fmol/ml) after hemodialysis were still higher than those in healthy subjects. On the other hand, a positive correlation (r = 0.65, p less than 0.05) between alpha hANP and creatinine in blood was found only in the group of chronic renal failure before maintenance hemodialysis. These results suggest that an impaired metabolism of alpha hANP in the kidney might play an important role in the elevation of plasma alpha hANP as well as the stimulation of alpha hANP secretion caused by the expansion of extracellular fluid.

Plasma and urine concentrations of atrial natriuretic peptide in patients with diabetes mellitus.

To examine whether plasma and urine concentrations of human atrial natriuretic peptide (hANP) are altered in patients with diabetes mellitus (DM), plasma and urine hANP concentrations were evaluated in 86 patients with diabetes mellitus using an extraction procedure. The mean recovery rate of extraction was 71.8 +/- 0.6% (mean +/- SEM). The major immunoreactive component of hANP in extracted plasma and urine appeared to be identical to synthetic alpha hANP as judged by reverse-phase high-performance liquid chromatography (HPLC). The patients were divided into three groups according to their renal complications. The patients in group 1 had no apparent abnormality in serum creatinine, serum or urine beta 2-microglobulin (beta 2-MG), or urine N-acetyl-beta-D-glucosaminidase (NAG); those in group 2 showed either beta 2-MG or NAG abnormality but no creatinine abnormality. The patients in group 3 were though to have an established diabetic nephropathy and showed a serum creatinine increase. Plasma ANP concentrations in groups 1, 2, and 3 were 10.7 +/- 2.1, 19.9 +/- 5.6, and 39.2 +/- 9.9 fmol/ml, respectively. These values in groups 2 and 3 were significantly higher than the control values (p less than 0.05 or p less than 0.01 versus 6.2 +/- 0.7 fmol/ml). Urine ANP concentrations in group 1 were also within normal range, though those in groups 2 and 3 markedly increased in comparison with normal values.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of growth hormone secretion by central administration of atrial natriuretic polypeptide in the rat.

Intracerebroventricular (icv) injection of alpha-human atrial natriuretic polypeptide (alpha hANP) or alpha-rat ANP (0.6 and 3 nmol/rat) elicited an increase in plasma GH levels both in conscious freely moving rats and in urethane-anesthetized rats when given at the trough of spontaneous GH secretion. Antiserum specific for rat GRF did not affect the plasma GH increase induced by icv injection of alpha hANP. Intracerebroventricular injection of alpha ANP (3 nmol/rat) failed to stimulate GH secretion in conscious rats pretreated with cysteamine (30 mg/100 g BW, sc), a depletor of somatostatin (SRIF), and in conscious rats during constant iv infusion of SRIF (55 ng/ml). GH release induced by iv injection of synthetic rat GRF (200 ng/100 g BW) was exaggerated by alpha hANP (3 nmol/rat, icv) in conscious rats. These results suggest that central ANP stimulates pituitary GH secretion possibly by inhibiting SRIF release from the hypothalamus in the rat.

Changes in the plasma and urine alpha human atrial natriuretic peptide (alpha hANP) concentration in patients with thyroid disorders.

In order to assess the possible involvement of thyroid hormone in alpha human atrial natriuretic peptide (alpha hANP), we investigated the plasma and urine ANP concentration in patients with primary hyperthyroidism and hypothyroidism. Plasma and urine were extracted through Sep-Pak C18 cartridges and the urine ANP concentration was corrected by urine creatinine (cre. mg/dl) and expressed as fmol/mg.cre.. The plasma ANP concentration in patients with untreated hyperthyroidism (32.3 +/- 7.0 fmol/ml; n = 22) was higher than in normal subjects (p less than 0.01 vs control; 6.2 +/- 0.7 fmol/ml). After restoration to euthyroidism, the plasma ANP concentration (patients with treated hyperthyroidism) fell to normal (8.9 +/- 1.9 fmol/ml). The plasma ANP concentration in patients with untreated hypothyroidism (14.1 +/- 3.0 fmol/ml; n = 7) was higher than normal, but in two of them there was mild renal dysfunction and an incomplete right blundle branch block in the electrocardiogram. It was possible that these factors contributed to the observed increase in plasma ANP. However, a significant positive correlation was found between plasma ANP and free thyroxine (n = 40, r = 0.449; p less than 0.01) and free triiodothyronine (n = 40, r = 0.546; p less than 0.01). The urine ANP concentration in patients with untreated hyperthyroidism was markedly higher than in normal subjects (p less than 0.01), but in untreated hypothyroidism not significantly different from normal.

Vasodilatory actions of alpha-human atrial natriuretic peptide and high Ca2+ effects in normal man.

To study vascular actions of synthetic alpha-human atrial natriuretic polypeptide (alpha hANP) in man, forearm blood flow (FBF) was measured by strain-gauge plethysmograph during the continuous infusion of 100 ng/min alpha hANP dissolved in 5% dextrose into the brachial artery in healthy subjects. alpha hANP increased FBF, with the concomitant increase in ipsilateral limb venous plasma concentrations of alpha hANP. Overall, there was a significant linear correlation between the decrements of ipsilateral forearm vascular resistance (FVR) during infusions of alpha hANP and initial FVR levels (r = -0.883, P less than 0.01). Moreover, alpha hANP, at the stepwise increasing doses of 20, 100, and 500 ng/min, increased FBF in a dose-related fashion: alpha hANP elicits a concentration-dependent vasodilation of forearm vascular beds. Concomitantly, infusions of alpha hANP caused a dose-dependent increase in ipsilateral limb venous plasma cyclic guanosine monophosphate (cyclic GMP). Overall, there were direct correlations of FBF either to ipsilateral venous plasma alpha hANP (r = 0.724, P less than 0.01) or to cyclic GMP concentrations (r = 0.637, P less than 0.01). Subsequently, isoosmolar CaCl2 solution was infused into the same brachial artery at a rate of 0.09 meq/min, and then, with a 2.5 +/- 0.2-mg/dl increase in ipsilateral venous serum calcium concentrations the incremental responses of both FBF and plasma cyclic GMP to alpha hANP were severely blunted. There was also a significant positive linear correlation between FBF and venous plasma cyclic GMP during infusions of alpha hANP with the simultaneous administration of CaCl2 (r = 0.807, P less than 0.01). Finally, the addition of CaCl2 infusion did not change the slope of the regression line of the FBF-plasma cyclic GMP relationship during infusions of alpha hANP. Evidence presented suggests that alpha hANP acts directly on the forearm vascular beds in man, eliciting its vascular relaxant effect, possibly by increasing cellular levels of cyclic GMP. Moreover, modest elevations of serum calcium inhibit the alpha hANP-dependent vasodilation, possibly through the suppression of cyclic GMP activation.

High plasma concentrations of human atrial natriuretic polypeptide in aged men.

To examine the effect of age on the secretion and action of human atrial natriuretic polypeptide (hANP), we compared plasma atrial natriuretic polypeptide and cGMP concentrations in 19 normal young (24-28 yr old) and 31 elderly (64-91 yr old) men. The mean basal plasma hANP level was 25 +/- 5 (+/- SEM) pg/ml in the young men and 120 +/- 22 pg/ml in the elderly men (P less than 0.01). The molecular size of plasma hANP in an aged man was similar to that of alpha hANP. The responses of plasma hANP and cGMP concentrations to an iv infusion of 500 ml 0.15 M NaCl also was compared. Mean plasma hANP concentrations increased significantly in both groups, and the response in the elderly men was exaggerated compared to that in the young men. However, the increases in plasma cGMP concentrations during NaCl loading were similar in both groups. We conclude that 1) the plasma hANP concentrations in healthy elderly men are higher than those in young men, and 2) the higher plasma hANP concentrations may be a compensatory response to reduced hANP activation of its receptors.

Increase in Circulating Insulin Induced by Atrial Natriuretic Peptide in Normal Humans

To search for possible metabolic interactions of alpha-human-atrial natriuretic peptide (alpha hANP), we evaluated in 20 normal subjects blood levels of alpha hANP, glucose, insulin, cortisol, electrolytes, catecholamines, free fatty acids, carnitine and amino acids, blood pressure (BP), and heart rate before, during, and after a 45-min infusion of synthetic alpha hANP. Group A [n = 10] was studied on liberal and Group B on three consecutive sodium (Na) intakes of 17, 140, and 310 mM/day. Plasma alpha hANP was slightly but not significantly higher following 5 days on "normal" or high than on low Na+ intakes. alpha hANP infused at 0.1 microgram/kg/min produced on all Na+ intakes comparable percentage increases in plasma insulin (+34 to 63%, p less than 0.001), norepinephrine (+76 to 155%, p less than 0.001) and heart rate (p less than 0.001), and a similar fall in diastolic BP (p less than 0.001). Plasma glucose tended to be decreased slightly and cortisol was reduced; epinephrine, dopamine, and potassium levels were not significantly modified. As evaluated in group A, serum free fatty acids were increased (p less than 0.01), plasma free carnitine levels were reduced (p less than 0.001), and amino acids were not consistently altered. These findings indicate that in normal humans alpha hANP may, on various sodium intakes, modulate insulin secretion and/or metabolism and elicit a possibly baroreflex-mediated sympathetic activation and lipolysis.

Renal, hemodynamic, and hormonal responses to atrial natriuretic peptide infusions in normal man, and effect of sodium intake.

The effect of 60-min constant iv infusions of alpha-human atrial natriuretic peptide (alpha hANP; 200 micrograms), sufficient to increase the steady state venous plasma alpha hANP concentration to levels found in patients with some circulatory disorders, was studied in six normal men equilibrated on a high sodium diet (200 mmol daily) and again when equilibrated on a low sodium intake (10 mmol daily). In each instance, the responses to alpha hANP were compared to those to control infusions given on the preceding day. The mean steady state plasma immunoreactive ANP concentration during the infusions was 320 pmol/liter and was the same during both diets. Thus, the MCR of alpha hANP was unaffected by major changes in sodium intake. Compared to control day observations, infusions of alpha hANP induced a more than 3-fold increase in sodium excretion and at least a 2-fold increase in urine volume and calcium and magnesium excretion in subjects ingesting 200 mmol sodium daily. During the low sodium diet, alpha hANP was still diuretic and induced comparable magnesium excretion, but the natriuresis was only 11% of that during the high salt diet. No significant changes in blood pressure or heart rate occurred during alpha hANP infusions during either diet, although during both diets there was a significant rise in plasma norepinephrine (P less than 0.02), which persisted well beyond the disappearance of immunoreactive ANP from plasma. Despite this sympathetic activation, renin and aldosterone production was reduced by alpha hANP. During low salt intake, alpha hANP significantly decreased PRA (mean pretreatment, 1.79; posttreatment, 1.25 nmol/liter/h; P less than 0.03), angiotensin II (mean pretreatment, 49; posttreatment, 28 pmol/liter; P less than 0.008), and plasma aldosterone (mean pretreatment, 554; posttreatment 307 pmol/liter; P less than 0.007), whereas values during control infusions did not change. Similar percent decreases in PRA and aldosterone also occurred during the high salt diet. Plasma cortisol and arginine vasopressin did not change during the alpha hANP infusions on either diet. We conclude that steady state levels of alpha hANP in plasma, similar to those in patients with some circulatory disorders, significantly increase sodium excretion and inhibit all elements of the renin-angiotensin-aldosterone system. The natriuretic, but not the hormonal or chronotropic, effects of alpha hANP are reduced by sodium depletion in normal man.

Depressor effects and release of atrial natriuretic peptide during norepinephrine or angiotensin II infusion in man.

Alpha-human atrial natriuretic peptide (alpha hANP) is the major circulating form of ANP in man. The potential of synthetic alpha hANP to antagonize the pressor action of norepinephrine (NE) or angiotensin II (AII) and a possible influence of NE or AII pressor infusions on circulating immunoreactive ANP (irANP) were investigated in 14 normal young subjects. After titration of doses to increase mean blood pressure by about 20 mm Hg, NE or AII was infused at a constant rate for 110 min. Mean blood pressure (BP) was similar during NE and AII infusions [109 +/- 4 (+/- SEM) and 108 +/- 3 mm Hg, respectively]. However, synthetic alpha hANP injected in stepwise increasing doses of 10, 40, and 75 micrograms caused significantly greater (P less than 0.001) BP reductions during NE infusion. alpha hANP lowered BP progressively from 147/91 +/- 5/3 to 136/70 +/- 5/3 mm Hg during NE infusion (P less than 0.001) and only minimally from 133/96 +/- 3/3 to 132/89 +/- 4/4 during AII infusion. Heart rate was elevated more (P less than 0.01) after alpha hANP injection during NE infusion. Endogenous plasma irANP increased significantly after 20 min of NE or AII pressor infusion (P less than 0.01 and P less than 0.05, respectively); this rise was more pronounced (P less than 0.05) during NE (from 25 +/- 2 to 80 +/- 20 pg/ml) than during AII (from 21 +/- 3 to 31 +/- 3 pg/ml) infusion. These findings suggest that alpha hANP interacted preferentially with noradrenergic as compared to angiotensinergic BP control. Conversely, for a given rise in BP, NE elicited a greater rise in circulating irANP.

Radioimmunoassay and characterization of atrial natriuretic peptide in human plasma.

A RIA for alpha-human atrial natriuretic peptide (alpha hANP) in plasma was developed and used to study the immunoreactive components secreted by the heart and circulating in peripheral venous plasma. The assay used [125I]diiodotyrosyl-alpha hANP, purified by high pressure liquid chromatography (HPLC), and a C-terminal-specific antiserum purchased from Peninsula Laboratories. Serial dilution curves of coronary sinus plasma samples were parallel with the standard curve, but significant nonparallelism was found in peripheral plasma samples of low immunoreactivity. When plasma was extracted using C-18 Sep-Pak cartridges, serial dilution curves from both coronary sinus and peripheral plasma samples were parallel to the standard curve. Although values for plasma samples assayed before and after extraction agreed closely (r = 0.99; n = 76), immunoreactive ANP in unextracted plasma was consistently greater (70-79 pmol/liter) than in extracts of plasma, suggesting non-specific interference by a component in plasma when assayed without extraction. Mean plasma immunoreactive ANP in 19 normal subjects consuming a normal salt intake was 14 +/- 1 (+/- SE) pmol/liter. In 5 normal men, increasing dietary sodium intake from 10 to 200 mmol sodium/day was associated with a 2-fold increment in ANP levels, and similar changes accompanied acute sodium loading using iv saline. Elevated values were found in patients with congestive heart failure (mean, 58 pmol/liter; range, 0-200; n = 9), chronic renal failure (mean, 118 pmol/liter; range, 30-290; n = 8), and primary aldosteronism (range, 32-90 pmol/liter; n = 3). HPLC and gel chromatographic analysis of the immunoreactive material found in coronary sinus plasma extracts showed that a large amount of the material eluted in the position of alpha hANP. A smaller quantity of immunoreactive material with a mol wt of about 1600 was also identified. Peripheral venous plasma extracts also contained several immunoreactive components, the largest amount of which corresponded to alpha hANP. The pattern of immunoreactive components in peripheral venous plasma, as identified by both gel chromotography and HPLC, was similar to that in coronary sinus plasma drawn during an active phase of hormone secretion. These findings indicate that the heart secretes alpha hANP or a closely similar peptide which is also present in peripheral venous plasma. Plasma immunoreactive ANP is responsive to sodium loading in normal man and is elevated in patients with hypervolemic disorders.

Lack of inhibitory effect of alpha-human atrial natriuretic polypeptide on aldosteronogenesis in aldosterone-producing adenoma.

The effects of synthetic alpha-human atrial natriuretic polypeptide (alpha hANP) on aldosteronogenesis in normal and aldosterone-producing adenoma cells (APA cells) in primary monolayer cultures were studied. alpha hANP significantly inhibited aldosterone secretion from normal adrenal cells in culture, but had no inhibitory effect on aldosterone secretion from APA cells in the presence or absence of 10(-8) M ACTH. alpha hANP enhanced the accumulation of intracellular cGMP in normal adrenal cells in culture, but not in APA cells. Visualization of [125I]iodo-alpha hANP-specific binding sites in APA and adjacent normal adrenal tissues by an in vitro receptor autoradiographic technique showed that these sites were localized only in normal adrenal tissue, but not in APA tissue. These results suggest that the lack of an inhibitory effect of alpha hANP on aldosteronogenesis in APA cells may be due to the absence of alpha hANP-specific receptor sites in APA cells.

Alpha-human atrial natriuretic polypeptide inhibits steroidogenesis in cultured human adrenal cells.

The ability of synthetic alpha-human atrial natriuretic polypeptide-(1-28) (alpha hANP) to alter steroidogenesis by human adrenal glands was investigated in primary human adrenal cell cultures. alphahANP (10(-9)-10(-7) M) inhibited basal and ACTH (10(-8) M)-stimulated aldosterone, cortisol, and dehydroepiandrosterone (DHEA) secretion in a dose-dependent manner. alpha hANP inhibited aldosterone (IC50, 1.3 X 10(-8) M) and cortisol (IC50, 0.7 X 10(-8) M) secretion more potently than it did DHEA (IC50, 7.5 X 10(-8) M) secretion. ACTH dose-dependent (10(-10)-10(-8) M) increases in aldosterone, cortisol, and DHEA secretion were significantly inhibited by alpha hANP (10(-8) M). In addition, alpha hANP enhanced the accumulation of intracellular cGMP in a dose-dependent manner. As aldosterone, cortisol, and DHEA secretion from cultured human adrenal cells was inhibited by alpha hANP, the site of inhibition of steroidogenesis by alpha hANP is probably localized in the early pathway of steroidogenesis in human adrenal cells. The results also suggest a link between inhibitory effects of alpha hANP and accumulation of intracellular cGMP.

Plasma Levels and Cardiovascular, Endocrine, and Excretory Effects of Atrial Natriuretic Peptide during Different Sodium Intakes in Man*

Endogenous plasma concentrations of human atrial natriuretic peptide (alpha hANP) as well as effects of synthetic alpha hANP on some cardiovascular, endocrine, and renal excretory parameters were investigated in 10 normal subjects during sodium (Na+) intakes of 17, 140, and 310 mmol/day, respectively. Plasma hANP was slightly but not significantly higher after 5 days of normal or high sodium intake than after 5 days of low sodium intake [54 +/- 13, 46 +/- 8, and 37 +/- 5 (mean +/- SEM) pg/ml, respectively]. alpha hANP infused at 0.1 microgram/kg X min during all Na+ intakes produced a similar fall in diastolic blood pressure (P less than 0.001) and rise in heart rate (P less than 0.001), a comparable percent increase in plasma norepinephrine (P less than 0.001), and a reduction in plasma cortisol and aldosterone (P less than 0.01-0.001) despite raised renin activity (P less than 0.05-0.001) and unchanged plasma electrolytes. alpha hANP-induced plasma volume contraction, diuresis, and natriuresis were greater during high than low Na+ intake (P less than 0.01-0.001). Therefore, in normal man different Na+ intakes are accompanied by marked modifications in renal excretory responsiveness to alpha hANP. Regardless of sodium intake, alpha hANP can promote BP reduction and hemoconcentration, elicit reflex (?) sympathetic activation, and depress basal circulating aldosterone and cortisol levels in the face of an activated renin system.

Atrial natriuretic peptide inhibits the aldosterone response to angiotensin II in man

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.