Dynamic cardiovascular responses to infusions of atrial natriuretic factor in humans

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

Hyperaldosteronism and hypertension: ethnic differences

The purpose of this study is to evaluate the relationship between aldosterone and blood pressure in a total of 220 normotensive and 293 essential hypertensive subjects in 2 genetically distinct populations-blacks and white French Canadians. The 24-hour blood pressure monitoring was performed under standardized conditions after discontinuing antihypertensive medications. Plasma renin activity and plasma aldosterone were measured in the supine position and after standing for 10 minutes. Plasma atrial natriuretic factor was also measured. Supine and standing plasma renin activities were lower (P< or =0.01), plasma aldosterone was higher (P<0.0001), and the aldosterone/renin ratios were higher (P<0.0001) in the hypertensive subjects. Atrial natriuretic factor was also higher in the hypertensive subjects (P<0.0001). Among blacks, blood pressures did not correlate with plasma renin activity. However, both average daytime and nighttime systolic and diastolic blood pressures were correlated with supine and standing plasma aldosterone and with the aldosterone/renin ratio (P<0.005 or less). In French Canadians, blood pressures tended to be positively correlated with standing plasma renin activity and aldosterone, but not with the aldosterone/renin ratio. Correlations of blood pressure with aldosterone were more consistent and more striking in blacks than in French Canadians. In both ethnic groups, there were inconsistent correlations of blood pressure with atrial natriuretic factor. These observations are consistent with the hypothesis that aldosterone-induced volume expansion is an important contributor to hypertension, especially in blacks.

[Endothelium-derived factors in hypertensive blood vessels, especially nitric oxide and hypertension]

Endothelium-dependent relaxation (EDR) in the blood vessels of spontaneously hypertensive rats (SHR) and the role of nitric oxide (NO) in the initiation of hypertension are reviewed. EDR was impaired in blood vessels of SHR depending on age and degree of hypertension when compared with those of normotensive rats. The cause of the impairment varied among the type of blood vessels: a decrease in the production of NO and endothelium-derived relaxing factor (EDRF) and an increase in the production of endothelium-derived contracting factor (EDCF) are the main causes of the impairment in large arteries, while a decrease in endothelium-dependent hyperpolarization and increased release of EDCF are the main causes of the impairment in small arteries. Interactions among these endothelium-derived factors and changes in the interactions are also causes of impairment. Superoxide may be involved in the impairment of EDR by destroying NO. The endothelium depresses smooth muscle contraction, including spontaneous tone developed in vascular smooth muscle, and the depressing effect of the endothelium is impaired in the preparations from SHR. The endothelium of blood vessels of SHR are structurally injured as demonstrated by scanning electron microscopy. Antihypertensive treatment prevented these functional and structural changes. Chronic treatment with inhibitors of NO production in normotensive rats impaired EDR and elevated blood pressure. The impairment of EDR is a secondary change due to continued hypertension, and early initiation of antihypertensive therapy is recommended.

Renal and vascular effects of C-type and atrial natriuretic peptides in humans

C-type natriuretic peptide (CNP) may affect renal and vascular functions differently from atrial natriuretic peptide (ANP). The objective of this study was to compare the renal and vascular actions of CNP to those of ANP in normal men. CNP or ANP (0.005, 0.01, and 0.05 microg x kg(-1) x min(-1)) were given by infusion to eight healthy volunteers. CNP caused dose-dependent increases in natriuresis (U(Na)) and in the fractional excretion of sodium (FE(Na)) with no effect on diuresis (UV), renal plasma flow, and glomerular filtration rate (GFR). Fraction of filtration (FF) increased only with the 0.05 microg x kg(-1) x min(-1) CNP dose. ANP caused larger increases in U(Na), FE(Na), and FF than CNP and also increased UV at 0.01 and 0.05 microg x kg(-1) x min(-1) and GFR at 0.05 microg x kg(-1) x min(-1). Although the ANP and CNP infusions produced similar elevation in the respective peptides plasma levels, urinary and nephrogenous guanosine 3',5'-cyclic monophosphate increased less in response to CNP than to ANP. Blood pressure, forearm blood flow, plasma renin activity, and aldosterone remained unaffected during the peptides infusion. Plasma ANP increased slightly during CNP infusion. Our data indicate a higher threshold of renal response to CNP than to ANP. In contrast to ANP, CNP probably may not act as an endocrine factor in humans.

Acute hemodynamic effects of combined inhibition of neutral endopeptidase and angiotensin converting enzyme in spontaneously hypertensive rats

Neutral endopeptidase inhibitors (NEPI) potentiate the hypotensive effect of converting enzyme inhibitors (CEI) in conscious spontaneously hypertensive rats (SHR) but the mechanism of this potentiation remains unknown. The present study assesses the hemodynamic effects of a CEI (enalaprilat 1 mg/kg; n = 9), a NEPI (retrothiorphan 25 mg/kg + 25 mg/kg/h; n = 9) and the combination (CEI+NEPI; n = 9) versus a control group (n = 9) in anesthetized spontaneously hypertensive rats. CEI alone induced a significant hypotensive effect due to a decrease (-35.1%) in total peripheral resistance (TPR), with no significant increase in cardiac output (CO). NEPI alone had a slight hypotensive effect due to a small decrease in CO. CEI+NEPI decreased the mean arterial pressure to the same extent (-26.7%) as the CEI-induced hypotensive effect, decreased TPR (-44.4%) and induced an increase in CO (+38.2%) with an increase in heart rate. In summary, NEPI combined with CEI induces large decreases in blood pressure and in TPR which do not significantly differ from the CEI-induced effects. It also induces increases in heart rate and in cardiac output in anesthetized SHR.

Atrial natriuretic peptide and its potential role in pharmacotherapy

Atrial natriuretic peptide (ANP) is a 28 amino-acid polypeptide secreted into the blood by atrial myocytes after atrial pressure and distension. Although its role in humans is not clear, it can produce a variety of physiologic effects including vasodilatation, natriuresis, and suppression of the renin-angiotensin-aldosterone axis. These actions are potentially useful in a variety of pathologic states such as hypertension and congestive heart failure, and diverse methods to augment the effects of ANP in these states have been devised. The results are exciting and, despite some problems, may lead to the pharmacologic use of enhancement of ANP actions in several clinical disorders.

Atrial natriuretic peptide alters neither capillary filtration nor vascular compliance of both skin and skeletal muscle of humans

We studied the effects of hANP 99-126 on capillary filtration and venous compliance in both the calf (mainly skeletal muscle) and foot (mainly skin) of humans. Six healthy mean received ANP (intravenous injection of 25 micrograms followed by continuous infusion of 0.1 microgram.kg-1.min-1) for 30 min. Another six men served as time controls. Capillary filtration coefficient, venous compliance, and also volume and blood flow of both calf and foot were measured repeatedly by occlusion plethysmography before, during, and after ANP. Additionally, we determined hematocrit, central venous pressure, venous pressure in the foot, arterial pressure, and heart rate. Filtration coefficients, venous compliance, blood flow of both calf and foot as well as arterial blood pressure did not change systematically during the infusion of ANP, and yet leg volume and central venous pressure (3.1 +/- 0.8 cm H2O) decreased while both hematocrit (3.1 +/- 1.0%) and heart rate (17 +/- 11 min-1) increased. Thus, the ANP-evoked decrease in central venous pressure and increase in hematocrit are unrelated to blood pooling or increases in capillary filtration in skeletal muscle and skin of healthy humans.

Atrial natriuretic factor: does it have a role in psychiatry?

Atrial natriuretic factor (ANF) is the first of a group of atrial natriuretic peptides (ANPs) discovered since 1981. This group of peptides is thought to have an important role in sodium homeostasis and regulation of fluid volume. Although the role of ANF in cardiovascular and renal disorders is under investigation, the specific signaling involvement that ANF may have in the central nervous system is still unexplored. To date, ANF has not as yet been associated with a given functional area in the brain, nor has it been shown to be linked to any particular psychopathology. Neuropharmacology research of these peptides and their drug manipulation is needed to advance our knowledge of the possible role of ANF in psychiatry beyond the current level of speculation.

Effect of intravenous atrial natriuretic peptide on gas exchange in humans

The aim of this work was to establish whether a physiological increase in atrial natriuretic peptide (ANP) plasma levels affects pulmonary gas exchange in humans. Ten volunteers received an infusion of either ANP (4 pmol.kg-1.min-1) or physiological saline, for 60 min. Baseline measures of the alveolar-arterial PO2 difference and of the physiological dead space were within normal limits and remained stable during and after the infusion of ANP or saline, although plasma ANP and cGMP rose significantly (p < 0.01) (mean +/- SEM: ANP: 13.4 +/- 3.9 to 56.0 +/- 10.4 pmol/l; cyclic GMP: 3.8 +/- 0.3 to 17.0 +/- 3.8 nmol/l). We conclude that a physiological increase in plasma ANP does not affect pulmonary gas exchange significantly in humans.

Blunted systemic, splanchnic, and renal hemodynamic responses to atrial natriuretic peptide in rats with cirrhosis

Systemic, splanchnic and renal hemodynamic responses to saline, physiological (25 ng.kg-1.min-1) and pharmacological (100, 300 and 600 ng.kg-1.min-1) doses of alpha human atrial natriuretic peptide were measured in normal (n = 7 for saline and 7-8 for each dose of atrial natriuretic peptide) and cirrhotic (n = 7 for saline and 7-8 for each dose of atrial natriuretic peptide), conscious, unrestrained rats. In addition, plasma norepinephrine concentrations were measured in normal and cirrhotic rats, before and following a 300-ng.kg-1.min-1 dose of atrial natriuretic peptide. In cirrhotic rats, splanchnic, renal and systemic hemodynamics were not significantly affected by either physiological or pharmacological doses of atrial natriuretic peptide. In normal rats, a 300 ng.kg-1.min-1 dose of atrial natriuretic peptide significantly decreased cardiac index, portal tributary blood flow and renal blood flow, and significantly increased vascular resistance in the systemic, portal, and renal territories. The other doses of atrial natriuretic peptide did not significantly change regional and systemic hemodynamics. Atrial natriuretic peptide-induced changes in plasma norepinephrine concentrations were significantly higher in normal than in cirrhotic rats (1827 +/- 834 vs. 59 +/- 46 pg/ml, mean +/- S.E., respectively). In conclusion, this study shows that the normal cardiovascular response to a 300 ng.kg-1.min-1 atrial natriuretic peptide infusion is blunted in cirrhotic rats. Moreover, in cirrhotic rats, blunting of vasoconstriction following atrial natriuretic peptide administration seems to be due to a lack of increased sympathetic vascular tone.

Atrial natriuretic peptide decreases hepatic and cardiac blood content, but increases intestinal blood content in supine humans

The authors evaluated in humans whether atrial natriuretic peptide (ANP) alters the regional distribution of blood in capacitance vessels. Eight healthy male volunteers (mean age: 30 years, range: 24-39) were studied twice. On different days and in a randomized, double blind fashion they received either alpha h-ANP (99-126), 25 micrograms intravenously followed by infusion of 0.1 microgram kg-1 min-1, or vehicle. Changes of regional blood content in heart, liver, and intestine were evaluated at 3-min intervals using autologous radioactively (99mTc) labeled red cells. Calf circumference (strain gauge), central venous pressure, and heart rate were recorded continuously while arterial pressure (oscillometry), hematocrit, ANP and cGMP plasma concentrations were determined intermittently. Exogenous ANP increased plasma concentrations of ANP (49 pg ml-1 +/- 8 SE to 614 +/- 190) and cGMP (1.7 pmol ml-1 +/- 0.2 to 30.8 +/- 4.4). This elicited significant and profound decreases in liver (-11%) and cardiac (-10%) radioactivity, contrasted by a smaller but significant increase (+4%) of intestinal radioactivity. These changes became gradually apparent about 15 min during ANP administration and reached their nadir at the end of the infusion period. Central venous pressure significantly decreased by 3.4 cm H2O and calf volume by 0.3 ml/100 ml while hematocrit increased by 2.6%. All changes were at least partly reversed when ANP administration ceased. Of note, two subjects developed a near syncope with abrupt bradycardia and arterial hypotension following an initial gradual decrease in cardiac counts and central venous pressure. We conclude that in humans ANP markedly alters the regional blood distribution in the capacitance vasculature as blood content decreased profoundly in both heart and liver, but increased in the intestine, albeit to a lesser extent. Accordingly, a redistribution of blood away from the heart represents another unique mechanism by which ANP can exert its cardiovascular actions.

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Hemodynamic and sympathetic responses to human atrial natriuretic peptide infusion in patients with cirrhosis

To determine the potential usefulness of atrial natriuretic peptide (ANP) in patients with cirrhosis, we examined the effects of the infusion of a low dose of alpha-human ANP (alpha hANP, 25 ng.kg-1.min-1 for 30 min) on renal, splanchnic, systemic hemodynamics and sympathetic outflow in eight patients. Pulmonary arterial plasma ANP concentrations increased from 59 +/- 9 to 328 +/- 41 pg/ml (mean +/- S.E., p less than 0.05). Mean values of glomerular filtration rate and renal plasma flow were not significantly changed. Individual renal plasma flow responses differed from one patient to another. Renal plasma flow increased in two patients, decreased in three and did not change in the other patients. Renal plasma flow changes were correlated with basal renal plasma flow values (r = -0.938, p less than 0.05) but not with arterial pressure changes or renal vein plasma norepinephrine concentration changes. Azygos blood flow increased from 0.43 +/- 0.10 to 0.63 +/- 0.13 l/min (p less than 0.05) and the hepatic-venous pressure gradient decreased from 19.9 +/- 1.5 to 17.5 +/- 2.9 mmHg in post-infusion (p less than 0.05). Mean arterial pressure decreased significantly by 18% and cardiac output by 12%. Systemic vascular resistance and pulmonary arterial plasma norepinephrine concentrations were not significantly modified. Thus, in patients with cirrhosis, alpha hANP appears to have a direct vasodilating action on renal arterioles when basal renal vascular tone is high. In addition, although alpha hANP might exert a portal hypotensive action, alpha hANP induced arterial hypotension as a result of both low cardiac output and a lack of increased sympathetic vascular tone. The arterial hypotensive action may, thus, limit the therapeutic use of low doses of alpha hANP in cirrhotic patients.

Atrial natriuretic factor as a vasodilator agent in hypertensive patients

To investigate the role of Atrial Natriuretic Factor (ANF) in modulating arteriolar tone in hypertension, a synthetic 25 AA human ANF-analogue (anaritide) was infused intraarterially in the forearm vascular bed of five patients with mild hypertension. A dose-dependent increase in blood flow (plethysmographic technique) was seen at rates covering a thousand-fold range (0.008, 0.08, 0.8, 8.0 micrograms/dl tissue/min x 15 minutes each). At the lowest infusion rate, the forearm blood flow increment was associated with changes in local venous ANF concentrations comparable with those reported during biological stimuli in hypertensive man and consistent with an ANF physiologic role in forearm arterioles of hypertensive patients. However, at local venous concentrations greater than 1000 pg/ml, ANF did not relax forearm vessels by more than about one-fourth of the total forearm vasodilator capacity (as assessed through a maximally active ischemic stimulus). These data confirm the low potency of ANF as an endogenous vasodilator, although vasodilator potency is not a necessary requirement for physiologic systems involved in the regulation of muscular vascular tone. Systemic arterial pressure, heart rate, and contralateral flow did not change during the study in spite of the markedly increased peripheral ANF levels recirculating from the local forearm administration. This behavior indicates that arteriolar vasodilation is apparently not the main mechanism of action of ANF on systemic hemodynamics in hypertensive patients.

Pathophysiologic levels of atrial natriuretic factor do not alter reflex sympathetic control: direct evidence from microneurographic studies in humans

To determine if circulating levels of atrial natriuretic factor comparable with those seen in pathophysiologic states alter autonomic control of the circulation, direct recordings of hemodynamic variables and efferent sympathetic nerve activity to muscle (microneurography) were obtained during two separate protocols in a total of 21 normal men (age 25 +/- 1 years). In protocol 1, the responses of 10 men were compared during incremental mechanical unloading of cardiopulmonary baroreceptors with lower body negative pressure versus responses to comparable unloading during infusion of alpha-human atrial natriuretic factor. Lower body negative pressure decreased pulmonary artery diastolic and right atrial pressures, did not alter arterial pressure or heart rate and increased muscle sympathetic nerve activity from 205.2 +/- 36.3 to 438.7 +/- 100.2 units/min (p less than 0.01). Intravenous infusion of atrial natriuretic factor (25 ng/kg per min) increased plasma levels of the hormone from 24 +/- 4 to 322 +/- 34 pg/ml (p less than 0.01, n = 6), produced similar decreases in pulmonary artery diastolic and right atrial pressures, did not alter arterial pressure, increased heart rate and increased sympathetic nerve activity from 233.1 +/- 35.6 to 387.2 +/- 64.9 units/min (p less than 0.05). Thus, during similar hemodynamic perturbations produced by lower body negative pressure or infusion of atrial natriuretic factor at the dose used in this study, these subjects exhibited comparable sympathoexcitatory responses, with a 109 +/- 23% increase in sympathetic activity during lower body negative pressure and a 76 +/- 19% increase during atrial natriuretic factor infusion (p = NS). In protocol 2, the responses of 11 additional men were examined during lower body negative pressure performed before and again during infusion of atrial natriuretic factor (12.5 ng/kg per min). During baseline (prehormone) trials, lower body negative pressure (-14.5 +/- 1.6 mm Hg) decreased central venous pressure, did not change arterial pressure or heart rate and increased sympathetic nerve activity from 215 +/- 47.7 to 372.3 +/- 64.3 units/min (p less than 0.001). Infusion of atrial natriuretic factor increased plasma levels of the hormone from 39 +/- 8 to 313 +/- 18 pg/ml (p less than 0.01, n = 7); central venous pressure was held constant during hormone infusion by intravenous infusion of saline solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial natriuretic factor-induced systemic vasoconstriction in conscious dogs, rats, and monkeys

This study addresses the hypothesis that atrial natriuretic factor (ANF) is a primary vasodilator, which reduces arterial pressure directly and increases total peripheral resistance secondarily by reflex mechanisms. The effects of 30-minute infusions of ANF (0.3 micrograms/kg/min i.v.) were examined in conscious dogs, rats, and monkeys before and after ganglionic blockade with hexamethonium. In seven intact, conscious dogs, ANF reduced mean arterial pressure by 7 +/- 1% and cardiac output by 19 +/- 3% and increased total peripheral resistance by 15 +/- 3%. After ganglionic blockade, ANF reduced mean arterial pressure by 7 +/- 2% but still increased total peripheral resistance by 15 +/- 3%. Similar results were observed in four dogs with total cardiac denervation and in six dogs with arterial baroreceptor denervation. Furthermore, in two dogs, combined ganglionic and alpha 1-adrenoceptor blockades failed to alter the rise in total peripheral resistance observed with ANF. In six intact, conscious rats, ANF reduced mean arterial pressure by 8 +/- 2% and cardiac output by 27 +/- 2% and increased total peripheral resistance by 27 +/- 5%. After ganglionic blockade, ANF still increased total peripheral resistance by 13 +/- 3%. In six intact, conscious monkeys, ANF reduced mean arterial pressure by 14 +/- 2% and cardiac output by 26 +/- 3% and increased total peripheral resistance by 17 +/- 3%. However, after ganglionic blockade. ANF decreased total peripheral resistance by 11 +/- 2%. These data provide evidence for a fundamental species difference in the vascular actions of ANF. In conscious dogs, ANF elicits "direct" vasoconstriction, which increases total peripheral resistance, even in the presence of denervation of reflexes or autonomic blockade. In conscious rats, ANF elicits both direct and reflexly mediated vasoconstriction. In conscious monkeys, although a component of direct vasoconstriction may also be present, the most prominent component appears to be reflexly mediated, since it was abolished by ganglionic blockade.

Hemodynamic interactions of atrial natriuretic factor with the sympathetic nervous system in sheep

The hemodynamic effects of short-term infusion of atrial natriuretic factor (ANF) were observed in sheep with combined alpha/beta adrenoceptor pharmacological blockade. The effect of ANF on the sympathetically-mediated baroreflex system was observed in conscious sheep in which aortic and vena caval balloon occluders had been surgically implanted. ANF infused at 100 micrograms/h for 60 min produced similar effects on blood pressure, cardiac output and stroke volume during alpha/beta-adrenoceptor blockade, compared to the responses seen in normal sheep, however the increases in heart rate and total peripheral resistance were reduced. ANF markedly enhanced the gain of the baroreceptor-heart rate reflex in the sheep. This effect may mediate the large increase in heart rate which is associated with a small fall in blood pressure during short-term infusion of ANF. In conclusion, the sympathetic nervous system plays an important role in regulating the reflex cardiovascular responses to short-term infusion of ANF in sheep. The large species variation in the hemodynamic responses to ANF may be related to differing degrees of stimulation or inhibition of the baroreceptor system to affect heart rate and/or peripheral resistance.

Prolonged low dose infusion of atrial natriuretic factor in essential hypertension

The C-terminal fragment of atrial natriuretic factor (ANF) was infused intravenously at 0.5 pmol/kg/min during 12 hours in 6 patients with mild to moderate essential hypertension, and in 6 normotensive volunteers, all recumbent and well hydrated, under a daily intake of 200 and 120 mmoles of sodium and potassium, respectively. Plasma C-terminal ANF tended to increase during ANF and to decrease during vehicle infusions. Plasma concentrations of the N-terminal fragment of ANF decreased by 20 to 40% (p less than 0.05) during ANF and remained unchanged following vehicle infusion, suggesting that exogenous ANF reduces endogenous ANF secretion. ANF increased significantly plasma cyclic guanosine monophosphate (p less than 0.01) from 3.1 +/- 0.4 to 4.3 +/- 0.8 and from 2.8 +/- 0.4 to 5.1 +/- 0.5 nmol/L in controls and patients respectively. ANF reduced systolic diastolic blood pressure during the last 8 hours of the infusion, by about 5% (p = 0.055) in patients, but did not alter blood pressure in controls. Sodium excretion during ANF increased 42% vs vehicle (p less than 0.05), in the patients group and remained unchanged in controls. Hematocrit levels increased significantly in both groups with ANF infusion. We conclude that a prolonged infusion of ANF at a physiological rate causes a modest increase in plasma cyclic guanosine monophosphate, hemoconcentration, and reduces endogenous ANF secretion. It also stimulates diuresis and natriuresis and slightly reduces systolic blood pressure in patients with essential hypertension.

Effect of plasma sodium on aldosterone secretion during angiotensin II stimulation in normal humans

Studies were carried out in normal male subjects (n = 6, age 20-35 years) to determine the interaction of angiotensin II and plasma sodium on aldosterone secretion. These relations were quantified by elevation of plasma sodium with an infusion of 5% sodium chloride (4 ml/kg/30 min i.v.) with measurements of plasma aldosterone, atrial natriuretic factor (ANF), and arginine vasopressin (AVP) over 3 hours. Two hours before sodium chloride infusion, an intravenous infusion of angiotensin II was begun at 0.5 or 5.0 ng/kg/min and continued throughout the study. Plasma potassium was maintained constant by the addition of potassium to the infusate. NaCl/KCl infusion raised plasma sodium 4 meq/l with no decreases of plasma potassium. Plasma aldosterone averaged 7 +/- 1.8 ng/dl before NaCl infusion in subjects infused with 0.5 ng angiotensin II and was not significantly reduced with sodium chloride infusion. Angiotensin II infused at 5 ng/kg/min resulted in average plasma aldosterone levels of 31 +/- 3.6 ng/dl, which sodium chloride infusion decreased to 16.6 +/- 1.3 ng/dl (p less than 0.05) in 60 minutes. Plasma aldosterone remained depressed for the remaining period of study. Plasma ANF increased from 40 to 60 pg/ml with sodium chloride infusion. We conclude that small physiological elevations of plasma sodium concentrations can signal substantial decreases of plasma aldosterone in normal human subjects in situations where plasma angiotensin II is moderately elevated. The precise mechanisms of these responses remain to be determined.