Inhibition of aldosterone production by an atrial extract

Plasma alpha natriuretic peptide in cardiac impairment

Regional plasma alpha human atrial natriuretic peptide concentrations were measured, and their relation to intracardiac pressures assessed, in an unselected series of 45 patients undergoing diagnostic cardiac catheterisation. Arteriovenous gradients in plasma concentrations of alpha human atrial natriuretic peptide were consistent with its cardiac secretion and its clearance by the liver and kidneys. Plasma concentrations of the peptide in the pulmonary artery, aorta, and superior vena cava correlated closely with the mean right atrial and pulmonary arterial pressures, and similar, though weaker, positive relations were seen with the left ventricular end diastolic and pulmonary artery wedge pressures. Concentrations of both atrial natriuretic peptide and renin showed significant inverse relations with serum sodium concentrations. Plasma concentrations of alpha human atrial natriuretic peptide are an additional objective indicator of the severity of haemodynamic compromise in patients with cardiac impairment.

Localization of specific binding sites for atrial natriuretic factor in peripheral tissues of the guinea pig, rat, and human

Specific, high affinity atrial natriuretic factor (ANF) binding sites were identified and localized by autoradiographic techniques in peripheral tissues of the guinea pig, rat, and human. In the guinea pig kidney, high concentrations of ANF binding sites were located in the glomerular apparatus, outer medulla, and small renal arteries. Other peripheral tissues containing ANF binding sites included the zona glomerulosa of the adrenal cortex, the smooth muscle layer of the aorta and gallbladder, the lung parenchyma, the posterior lobe of the pituitary, the ciliary body of the eye, and the leptomeninges and choroid plexus of the brain. The distribution of ANF binding sites in the rat and human kidney was nearly identical to those seen in the guinea pig kidney; high concentrations were present in the glomerular apparatus, outer medulla, and small renal arteries. These results are consistent with earlier physiological and pharmacological studies that suggested that ANF plays a functional role in the regulation of extracellular fluid volume and blood pressure. There appears to be little species variation in the location and concentration of renal ANF binding sites, suggesting that, at least in the kidney, the results in experimental animals are relevant to the actions of ANF in humans. The finding that ANF binding sites were stable and present in high concentrations in human postmortem kidneys further suggests that these tissues may be amenable to testing for the involvement of ANF receptor dysfunction in diseases such as hypertension and congestive heart failure.

Alpha-human atrial natriuretic polypeptide reduces the plasma arginine vasopressin concentration in human subjects

The synthetic alpha-human atrial natriuretic polypeptide (alpha-hANP) was infused into six normotensive, euvolaemic, healthy volunteers to examine the effect on the plasma arginine vasopressin (AVP) concentration. The intravenous administration of alpha-hANP (0.1 microgram/kg/min, 20 min) led to a remarkable reduction in mean blood pressure (-10 mmHg, P less than 0.05), and there was an increase in pulse rate (+10 bpm, P less than 0.05), in each subject. The urinary volume, sodium excretion and cyclic 3',5'-guanosine monophosphate (cyclic-GMP) excretion were increased to 3.5 (P less than 0.05), 2.5 (P less than 0.05) eight-fold (P less than 0.01), respectively, during the alpha-hANP infusion. The dose and duration of the synthetic alpha-hANP in the present study was sufficient to induce these cardiovascular and renal effects. The plasma AVP concentrations decreased from 0.39 +/- 0.09 pg/ml to the undetectable level during the alpha-hANP administration. After infusion, the plasma concentrations of the AVP promptly returned to preinfusion levels (0.46 +/- 0.14 pg/ml). However, there was no significant change in plasma AVP concentration during placebo infusion. The marked suppression in plasma AVP concentration may account for the remarkable diuresis, in addition of the direct renal effects of the synthetic alpha-hANP.

Mechanism of vasodilation induced by alpha-human atrial natriuretic polypeptide in rabbit and guinea-pig renal arteries

Effects of alpha-human atrial natriuretic polypeptide (alpha-HANP) on electrical and mechanical properties of smooth muscle cells of the guinea-pig and rabbit renal arteries and of the guinea-pig mesenteric artery were investigated. alpha-HANP (up to 10 nM) modified neither the membrane potential nor resistance of smooth muscle cells of the guinea-pig and rabbit renal arteries. In the guinea-pig mesenteric and renal arteries, alpha-HANP (up to 10 nM) had no effect on the amplitude and facilitation (mesenteric artery) or depression (renal artery) of excitatory junction potentials nor on action potentials. In the guinea-pig renal artery, alpha-HANP (up to 10 nM) had no effect on the depolarization induced by noradrenaline (NA) (up to 10 microM) but markedly inhibited NA-induced contraction. alpha-HANP (10 nM) slightly inhibited the K-induced contraction. In the rabbit renal artery, alpha-HANP (10 nM) inhibited the NA-induced contraction and to a lesser extent the K-induced contraction. In the rabbit renal artery, the effects of alpha-HANP on the release of Ca from the cellular storage by two applications of NA, and its re-storage, were investigated in Ca-free solution containing 2 mM-EGTA. When 5 nM-alpha-HANP was applied before and during the first application of 0.5 microM-NA, the contraction was markedly inhibited but the contraction to a second application of 10 microM-NA was potentiated. If the first dose of NA was 10 microM the effect was very small. Under the same experimental procedures, nitroglycerine (10 microM) showed almost the same effects as alpha-HANP on the NA-induced contractions. When both the first (3 mM) and second (10 mM) contractions were evoked by caffeine in Ca-free solution, alpha-HANP (5 nM) and nitroglycerine (10 microM) inhibited both contractions to the same extent. In the rabbit renal artery, applications of alpha-HANP or nitroglycerine increased the amount of guanosine 3',5'-phosphate (cyclic GMP) in a dose-dependent manner. However, a much higher concentration of nitroglycerine was required (2 X 10(3) times). In the rabbit renal artery, hydrolysis of phosphatidyl inositol 4,5-bisphosphate (PI-P2) activated by 0.5 microM-NA was inhibited by alpha-HANP, in a dose-dependent manner, but activation by 10 microM-NA was not inhibited by alpha-HANP (up to 100 nM).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of atrial natriuretic factor on the plasma aldosterone response to potassium infusion in rats--in vivo study

Previous in vitro studies have shown that atrial natriuretic factor inhibits the secretion of aldosterone stimulated by AII, ACTH, and potassium in adrenal cell suspensions. The present study investigated the effects of atriopeptin II on the plasma aldosterone response to a potassium infusion in conscious unrestrained rats in vivo. The infusion of potassium chloride solution increased plasma aldosterone level from 20.4 +/- 3.7 to 168.4 +/- 27.3 ng/dl. The simultaneous administration of atriopeptin II reduced the increase in plasma aldosterone level (16.0 +/- 2.1 to 63.3 +/- 10.4 ng/dl). There was no significant difference in the plasma renin activity, corticosterone, or serum potassium levels between the two groups. These results suggest that atriopeptin II may be important in the regulation of aldosterone secretion.

Atrial natriuretic factor regulates steroidogenic responsiveness and cyclic nucleotide levels in mouse Leydig cells in vitro

The effects of synthetic atrial natriuretic factor (ANF) on the regulation of mouse Leydig cell steroidogenesis have been studied in vitro. ANF in nanomolar concentration increased testosterone production by more than 30-fold over basal levels. Concomitantly, cyclic guanosine monophosphate levels were increased 35-fold; cyclic adenosine monophosphate levels fell minimally (15-20%). ANF at low concentration (1 X 10(-11) M) inhibited testosterone production by luteinizing hormone-stimulated cells, while at higher concentration (greater than 2 X 10(-9) M) ANF stimulated steroidogenesis beyond the level attained by luteinizing hormone alone. These results indicate that ANF can exert stimulatory effects on testosterone steroidogenesis in vitro, and that the mechanism may involve an intracellular messenger other than cyclic adenosine monophosphate.

Atrial pressure and secretion of atrial natriuretic factor into the human central circulation

Atrial natriuretic factor, a peptide found in mammalian cardiac atria, has natriuretic and vasodilatory properties that may be important in the regulation of intravascular volume. To study factors related to its release in human subjects, intracardiac pressures and plasma atrial natriuretic factor concentrations in the central circulation were measured in 34 patients with a variety of cardiovascular disorders. Plasma atrial natriuretic factor concentration increased from the inferior vena cava to the right atrium (76 +/- 24 to 162 +/- 37 pg/ml, p less than 0.001) and from the vena cava to the aorta (76 +/- 24 to 177 +/- 46 pg/ml, p less than 0.001). Mean right atrial pressure was positively correlated with atrial natriuretic factor concentration in the pulmonary artery (r = 0.58, p less than 0.001), and mean pulmonary capillary wedge pressure was positively correlated with concentration in the aorta (r = 0.64, p less than 0.001). In six patients whose atrial natriuretic factor concentrations were measured at two different levels of atrial pressure, increased atrial pressure was accompanied by increased atrial natriuretic factor concentration in the pulmonary artery (p less than 0.01) and aorta (p less than 0.01). Atrial natriuretic factor levels measured in fresh myocardium from a patient undergoing cardiac transplantation showed tissue concentrations in the atria 500-fold higher than tissue concentrations in the ventricles. These data document that atrial natriuretic factor is found in human atrial myocardium and suggest that it may be released in response to increased atrial pressure. Such a secretory release mechanism is consistent with the hypothesis that atrial natriuretic factor plays a role in the regulation of circulatory volume.

Atriopeptins and renal cortical and papillary blood flow

Studies were made of the effect of two pure synthetic atrial natriuretic factors (ANF) on renal cortical and papillary blood flow and on the excretion of sodium, potassium and water in young Munich Wistar rats by means of laser-Doppler flowmetry. The effects of Atriopeptin I (AP I), which selectively relaxes intestinal smooth muscle, were compared with those of Atriopeptin II (AP II), which relaxes both vascular and intestinal smooth muscle. Both peptides were administered by continuous intravenous infusion at 10 micrograms h-1 kg-1 body wt after a control period. A time control group was studied in parallel to see whether the variables investigated varied with time. In rats receiving vehicle alone (time control) and in those receiving AP I, there was no significant change either in the cortical or papillary blood flow, or in blood pressure (BP). The AP II infusion resulted in an increase in blood flow which was only transient despite the continuous infusion. Cortical blood flow increased by 22% (peak value) and papillary blood flow increased by 95% (peak value). The blood pressure (BP) decreased by 12% to a steady state level (103 +/- 2 vs. 91 +/- 2 mm Hg). The AP I caused a steady two-fold increase in sodium excretion (UNaV), a 35% increase in potassium excretion (UKV) and and 85% transient increase in urine flow rate (V). Infusion of AP II resulted in a more than 60-fold increase in UNaV during the period of increased blood flow, and then reached a steady state level 10 times higher than the control value.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat atriopeptin III alters hypothalamic neuronal activity

The effect of pressure application of rat atriopeptin III on extracellularly recorded action potentials of 39 hypothalamic neurons was studied in chloral hydrate-anesthetized male rats. Thirteen of these neurons were histologically located within the boundaries of the paraventricular nucleus. Atriopeptin III was a potent inhibitor of the spontaneous activity of 5 (38%) of these neurons and increased the spontaneous activity of one (8%) other neuron (7 paraventricular neurons were unresponsive to atriopeptin III). Neurons not located within the paraventricular nucleus responded similarly to pressure application of atriopeptin III. Twenty-seven percent (n = 7) were inhibited and 12% (n = 3) were excited while the remaining 16 (61%) neurons were unresponsive to atriopeptin III. Similar applications of an inactive fragment of atriopeptin III (amino acid sequence 18-28) did not alter the spontaneous activity of any neuron (n = 6). These results illustrate that atriopeptin III, an atrial peptide which is also present in the brain, can alter the spontaneous activity of hypothalamic neurons. This provides additional evidence for central activity of this peptide.

Testosterone production by mouse Leydig cells is stimulated in vitro by atrial natriuretic factor

The synthetic atrial peptides, rat atrial natriuretic peptide, atriopeptin I and atriopeptin II, stimulated testosterone production by mouse Leydig cells in a time- and concentration-dependent manner. The maximum stimulation of the steroidogenesis in response to the peptides was 6-10-fold over the basal level, as compared with 20-24-fold stimulation obtained with saturating concentrations of hCG. The stimulation of steroidogenesis by the most potent peptide, atriopeptin II, was markedly enhanced in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, suggesting an involvement of cyclic nucleotides. However, neither basal nor hCG-stimulated levels of cAMP were altered by the peptide, though testosterone production in response to submaximal concentrations of hCG was increased in the presence of atriopeptin II. The nature of the second messenger involved and the mechanism of action of the atrial peptides may be elucidated by further research in progress.

Distribution and coregulation of three peptide receptors in adrenals

Receptors sites for angiotensin II and atrial natriuretic factor were concentrated in the zone glomerulosa of the adrenal cortex in the rat, mouse, hamster, rhesus monkey, guinea-pig and the cow. Angiotensin Ii receptor sites were also accumulated in adrenal medullary tissue of the rat, mouse and the hamster. With exception of the cow the zonae fasciculata and reticulata of the adrenal cortex were not labelled with the angiotensin II ligand, but showed a moderate density of atrial natriuretic factor receptor sites in all species except the rhesus monkey. In comparison, somatostatin receptors were even more heterogeneously distributed in all species mentioned above. In the rat, the increased growth of zona glomerulosa cells found after three weeks of sodium deprivation was accompanied by a similar increase in number of receptor sites for angiotensin II, atrial natriuretic factor and somatostatin. This shows that all three peptide receptors are regulated simultaneously by a single metabolic disturbance, suggesting that they might be localized on the same cell type in the adrenal cortex.

Immunoreactive atrial natriuretic hormone levels increase in deoxycorticosterone acetate-treated pigs

Extensive evidence reported here and elsewhere indicates a hormonal role for atrial natriuretic factor. In the light of this evidence, it appears that atrial natriuretic hormone is a more appropriate term for these peptides than atrial natriuretic factor. Plasma levels of immunoreactive atrial natriuretic hormone were measured daily in seven pigs before and 1 week after subcutaneous implantation of deoxycorticosterone acetate (DOCA). Nine other animals underwent daily measurements of mean arterial pressure and central venous pressure during similar treatments. Plasma immunoreactive atrial natriuretic hormone levels rose progressively during the first 3 days after implantation, from a basal level of 60 +/- 9 pmol/L to a peak level of 159 +/- 21 pmol/L (p less than 0.05), and they remained significantly elevated throughout the rest of the 7-day observation period. In two animals that were restudied 6 weeks after DOCA implantation, plasma immunoreactive atrial natriuretic hormone had returned to preimplantation levels. The rise in plasma hormone levels after DOCA implantation closely paralleled the previously reported time course of mineralocorticoid escape. Whether atrial natriuretic hormone plays an important part in the escape phenomenon remains to be determined.

Platelet binding sites for atrial natriuretic factor in humans. Characterization and effects of sodium intake

Platelets bear receptors for vasoactive peptides such as angiotensin II and vasopressin. The presence of binding sites for another vasoactive peptide, atrial natriuretic factor, was therefore investigated in human platelets. 125I-labeled synthetic atrial natriuretic factor bound specifically to human platelets. Steady-state and kinetic experiments demonstrated the existence of one class of high-affinity low-capacity binding sites for atrial natriuretic factor in platelets with a dissociation constant of 30 pM. The order of potency of atrial natriuretic factor fragments showed that the structural requirements of the high-affinity binding site detected were similar to those of receptors for atrial natriuretic factor in rat blood vessels and adrenal zona glomerulosa. To study the regulation of these binding sites by sodium, normal young men were subjected successively in random order to a low-sodium (40 mmol per day) and high-sodium (300 mmol per day) diet for 4 days. Binding of atrial natriuretic factor to platelets was higher with the low-sodium diet (10.3 +/- 1.0 sites per cell) than with the high-sodium diet (7.1 +/- 0.7 sites per cell). In conclusion, human platelets bear binding sites for atrial natriuretic factor, the density of which may be modulated by sodium intake. The platelet is a useful model for investigating atrial natriuretic factor receptors in different physiopathological conditions in humans.

Four-hour infusions of synthetic atrial natriuretic peptide in normal volunteers

Two doses of synthetic atrial natriuretic peptide (0.5 and 5.0 micrograms/min) and its vehicle were infused intravenously for 4 hours in eight salt-loaded normal volunteers, and the effect on blood pressure, heart rate, renal hemodynamics, solute excretion, and secretion of vasoactive hormones was studied. The 0.5 micrograms/min infusion did not alter blood pressure or heart rate, whereas the 5.0 micrograms/min infusion significantly reduced the mean pressure by 20/9 mm Hg after 2.5 to 3 hours and increased the heart rate slightly. Inulin clearance was not significantly changed, but the mean p-aminohippurate clearance fell by 13 and 32% with the lower and higher doses, respectively. Urinary excretion of sodium and chloride increased slightly with the lower dose. With the higher dose, a marked increase in urinary excretion of sodium, chloride, and calcium was observed, reaching a peak during the second hour of the infusion. Potassium and phosphate excretion did not change significantly. A brisk increase in urine flow rate and fractional water excretion was seen only during the first hour of the high-dose infusion. Signs and symptoms of hypotension were observed in two subjects. No change in plasma renin activity, angiotensin II, or aldosterone was observed during either infusion, but a marked increase occurred after discontinuation of the high-dose infusion. In conclusion, the 5 micrograms/min infusion induced a transient diuretic effect, delayed maximal natriuretic activity, and a late fall in blood pressure, with no change in inulin clearance but a dose-related decrease in p-aminohippurate clearance. Despite large amounts of sodium excreted and blood pressure reduction, no counterregulatory changes were observed in the renin-angiotensin-aldosterone system or plasma vasopressin levels during the infusion.

Evidence for alpha-1 adrenergic receptor regulation of atriopeptin release from the isolated rat heart

Atrial myocardium is the source of a recently described peptide hormone termed atriopeptin. Atriopeptin is thought to have a role in the regulation of systemic arterial pressure, fluid balance and plasma electrolyte homeostasis. Isolated rat hearts release atriopeptin into the coronary effluent, and we have found that this release is stimulated by the administration of norepinephrine, a compound with alpha and beta adrenergic properties. Infusion of the pure beta-receptor agonist, isoproterenol, failed to stimulate the release; however, the alpha-1 receptor agonist phenylephrine induced the release in a dose-dependent manner. The stimulation of atriopeptin release by norepinephrine and phenylephrine was inhibited by alpha-blockade with phentolamine. Administration of BHT-920, a selective alpha-2 agonist, had no effect on atriopeptin release. We conclude that atriopeptin secretion by the atrial myocyte is stimulated by activation of the alpha-1 adrenergic receptor. This finding suggests an involvement of the sympathetic nervous system in the physiologic regulation of the secretion of this hormone.

Circulating atrial natriuretic peptides in conscious rats: regulation of release by multiple factors

Cardiocytes in the atria contain a prohormone that gives rise to atrial natriuretic peptides (ANP's), which have intrinsic hemodynamic regulatory activity. The distribution of ANP's in the brain suggests the involvement of these peptides in central cardiovascular regulation. In conscious rats with chronic indwelling catheters, volume loading with isotonic saline or glucose increased the amount of circulating immunoreactive ANP's by a factor of 4 to 5, as determined by radioimmunoassay. Hyperosmotic challenge with a hypertonic NaCl solution or anesthesia with halothane caused similar increases in plasma ANP's. Results obtained with the denervated-heart preparation indicate that neuronal influences are important in the release of ANP's induced by volume loading. As judged from reversed-phase high-performance liquid chromatography of extracted plasma and radioimmunoassay of collected fractions, the circulating physiologically important ANP's in the conscious rodent appear to be alpha-rANP(5-28) (atriopeptin III) and either alpha-rANP(3-28) [ANF(8-33)] or alpha-rANP(1-28) (ANF).

George E. Brown memorial lecture. Role of atrial peptides in body fluid homeostasis

Extracts of mammalian atria, but not ventricles, induce marked diuresis, natriuresis, and reduction in blood pressure when infused systemically in rats and dogs. These extracts also inhibit aldosterone biosynthesis and renal renin release. Natriuretic peptides, 21 amino acids and longer, have been isolated from atria of rodents and man, and share a nearly homologous amino acid sequence at the carboxyterminus. Natriuretic activity resides in a 17-amino acid ring formed by a disulfide bridge, and the C-terminal Phe-Arg appears necessary for full biological potency. The deoxyribonucleic acid-encoding atrial natriuretic peptides have been cloned and the gene structure elucidated. Reduction of the diuretic and natriuretic responses to an acute volume load by right atrial appendectomy first suggested a role for atrial peptides in the physiological response to plasma volume expansion. Subsequently, release of peptides with natriuretic and spasmolytic properties from isolated heart preparations in response to right atrial distension was demonstrated by bioassay and radioimmunoassay. The presence of these peptides in normal rat and human plasma in concentrations of 20-100 pM, and the findings of increased levels in response to acute and chronic plasma volume expansion, rapid atrial tachyarrhythmias, systemic hypertension, congestive heart failure, and renal insufficiency imply that they play an important role in body fluid homeostasis. The mechanisms by which atrial peptides increase renal salt and water excretion are as yet unclear. Renal vascular effects have been consistently demonstrated, and limited evidence for direct actions on tubule ion transport has also been reported recently. In vitro, these peptides cause precontracted vascular and nonvascular smooth muscle to relax, mediated by a direct action on smooth muscle cells. Specific receptors for these peptides have been characterized in crude membranes prepared from whole kidney homogenates and adrenal glomerulosa cells, in intact glomeruli and cultured glomerular mesangial cells, and in intact bovine aortic smooth muscle and endothelial cells. Natriuretic peptides stimulate cyclic guanosine monophosphate accumulation in target tissues, and augment particulate guanylate cyclase activity in membrane fractions, suggesting that cyclic guanosine monophosphate is the second messenger mediating their cellular action.

Atrial natriuretic factor receptors in rat kidney, adrenal gland, and brain: autoradiographic localization and fluid balance dependent changes

Mammalian atria contain natriuretic peptides designated atrial natriuretic factors (ANF). Using in vitro autoradiography with 125I-labeled ANF, we have localized high-affinity (Kd = 150 pM) ANF binding sites to the glomeruli of the kidney, zona glomerulosa of the adrenal gland, and choroid plexus of the brain. The numbers of sites in both kidney and adrenal are increased in rats deprived of water; increases are detectable within 72 hr of water deprivation in the kidney and within 24 hr in the adrenal gland. Receptor numbers decline in rats given 2.0% NaCl as drinking water and in diabetic rats. The discrete localizations and dynamic alterations of these receptors suggest that ANF regulates fluid balance through diverse but coordinated effects on receptors in numerous organs including the kidney, adrenal, and brain.

Increased release of atrial natriuretic polypeptides in rats with DOCA-salt hypertension

This study compared atrial and plasma concentrations of immunoreactive alpha-rat atrial natriuretic polypeptide (i alpha-rANP) in rats given tap water (control), a 1% saline solution (salt), deoxycorticosterone acetate (DOCA) and DOCA plus 1% saline solution (DOCA-salt) after 1 and 8 weeks of treatment. DOCA (100 mg/kg) was given by implanting a piece of silicon rubber impregnated with DOCA subcutaneously. Atrial i alpha-rANP increased, while plasma i alpha-rANP decreased with time in all groups. Atrial concentration of i alpha-rANP was significantly lower in the DOCA-salt group than in the other groups at 1 week, and was reduced in the DOCA and DOCA-salt groups as compared to the control group at 8 weeks. On the other hand, plasma concentration of i alpha-rANP was significantly higher in the DOCA and the DOCA-salt groups than in the control group at 1 week; the DOCA and DOCA-salt group values were also higher than the control and salt group values at 8 weeks. Atrial concentration of i alpha-rANP was inversely correlated with systolic blood pressure in the all rats at 1 week (r = 0.48, p less than 0.001) and at 8 weeks (r = 0.33, p less than 0.05). Plasma concentration of i alpha-rANP was positively correlated with systolic blood pressure at 8 weeks (r = 0.37, p less than 0.05). In addition, there was a significant positive correlation between plasma/atrial ratio of i alpha-rANP concentration and systolic blood pressure at either stage (r = 0.41, p less than 0.01 at 1 week; r = 0.40, p less than 0.01 at 8 weeks). Thus, it seems likely that the release of ANPs is increased in response to expansion of extracellular fluid volume or elevation of blood pressure, modifying the development of hypertension in DOCA-salt rats.

Release of immunoreactive atrial natriuretic factor from rat hypothalamus in vitro

Atrial natriuretic factor (ANF) had been found in brain tissues. Its role and the mechanisms by which it is produced and functions in the brain were not clear. We have initiated in vitro studies to find whether it is released from brain tissue and to elucidate the mechanism of its release. ANF was found to be released from rat hypothalamus by a depolarizing concentration of potassium and by a calcium-dependent mechanism. The ANF released was found to be predominantly a low molecular weight form. A small amount of high molecular weight form was also released. These results suggest that ANF produced in brain tissues is released, by a depolarization-induced and calcium-mediated mechanism, presumably from neuronal cells.

Captopril antagonizes the hypotensive action of atrial natriuretic peptide in the anaesthetized rat

Atrial natriuretic peptide (8-33; ANP) caused a prolonged hypotensive response following intravenous injection in anaesthetized rats. This response was abolished by captopril treatment and restored by concomitant angiotensin II infusion. These results suggest that ANP exerts its hypotensive action in the anaesthetized rat by the antagonism of the vasoconstrictor action of endogenous angiotensin II.

Rat atrial natriuretic factor suppresses proopiomelanocortin-derived peptides secretion from both anterior and intermediate lobe cells and growth hormone release from anterior lobe cells of rat pituitary in vitro

Synthetic rat atrial natriuretic factor (ANF) was found to attenuate, in a dose-dependent manner, basal and corticotropin-releasing factor-induced secretion of proopiomelanocortin-derived peptides from cultured anterior and intermediate lobe cells of rat pituitary. ANF was also found to suppress basal and growth hormone-releasing factor-stimulated secretion of growth hormone from anterior lobe cells of rat pituitary. These results, together with reports of the existence of ANF-positive neurons in the hypothalamus and ANF-positive fibers in the median eminence, suggest that hypothalamic ANF is probably involved in the regulation of pituitary hormone secretion, especially that of proopiomelanocortin-derived peptides and growth hormone.

Additive effects of atrial natriuretic polypeptide and of renal vasodilating agents in the anesthetized dog

In order to examine the contribution of an increase in renal papillary plasma flow to the mechanism of natriuresis by atrial natriuretic polypeptide (ANP), we compared the natriuretic effects of ANP administered into the renal artery of the dog together with secretin or acetylcholine (ACh). At an equivalent renal vasodilating dose, ACh increased urinary excretion of sodium (UNaV) to 212 +/- 36% of the control associated with a decrease in urine osmolality (62 +/- 6%), whereas secretin did not change UNaV (113 +/- 12%) or urine osmolality (101 +/- 14%). This result was compatible with the view that ACh causes natriuresis mainly by increasing papillary plasma flow. Combined administration of ANP with secretin caused a marked increase in UNaV to 407 +/- 55%, in association with a decrease in urine osmolality to 55 +/- 9%, suggesting that ANP may cause natriuresis by a mechanism similar to that of ACh. Combined administration of ANP with ACh further increased UNaV to 323 +/- 67% and decreased urine osmolality to 50 +/- 6%. These observations suggest that ANP and ACh share common but not identical mechanisms of natriuretic action since ANP caused additional natriuresis during ACh infusion. These findings, however, do not necessarily exclude the possibility that ANP also inhibits renal sodium reabsorption by a direct action.

Receptors for atrial natriuretic factor in cultured vascular smooth muscle cells

The presence of receptors for atrial natriuretic factor (ANF) was previously demonstrated in the mesenteric vascular bed in rats. Cultured vascular smooth muscle cells obtained from mesenteric arteries of rats were examined for binding of ANF. Saturation and competition experiments demonstrated the presence of a single class of receptors for ANF with high affinity (16 pM) and low capacity. Binding was specific. Kinetic studies showed a dissociation constant which agreed with that obtained at equilibrium in saturation and competition experiments. The exposure of the cells to unlabeled ANF for at least 24 hours showed that ANF may regulate its own receptors in smooth muscle under certain physiological conditions.

Heterologous radioimmunoassay of atrial natriuretic polypeptide in dog and rabbit plasma

Atrial natriuretic peptide (ANP) was measured in plasma of dogs and rabbits by radioimmunoassay (RIA) using a commercially available anti alpha-ANP serum and compared to our measurements of ANP in rats and humans. Plasma concentration of ANP in dog coronary sinus (234.9 +/- 41.0 pg/ml) was significantly greater than in systemic arterial blood (81.2 +/- 8.4 pg/ml). Gel filtration of dog coronary sinus plasma resulted in an ANP peak with the elution volume (Ve) of synthetic atriopeptin III (AIII) and a minor peak eluting with the void volume (Vo). Rabbit systemic arterial plasma ANP was 53.3 +/- 4.3 pg/ml and yielded one peak, with a Ve of AIII. Ion exchange chromatography of dog and rabbit atrial extracts (AE) resulted in a major ANP region which resembled AIII. Gel filtration of AE showed larger molecular species as well as AIII. Dilutions of dog and rabbit plasma and AE were parallel with the AIII standard in radioimmunoassay.

Blood levels and renal effects of atrial natriuretic peptide in normal man

Since mammalian atria were recently found to contain vasoactive and natriuretic peptides, we investigated the following in normal humans: plasma human atrial natriuretic peptide concentrations, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), urinary water and electrolyte excretion, blood pressure (BP), and catecholamine, antidiuretic hormone (ADH), angiotensin II, and aldosterone levels before, during, and after intravenous administration of the newly synthetized alpha-human atrial natriuretic peptide (alpha hANP). In 10 subjects alpha hANP given as an initial bolus of 50 micrograms followed by a 45-min maintenance infusion at 6.25 micrograms/min increased plasma alpha hANP from 58 +/- 12 to 625 +/- 87 (mean +/- SEM) pg/ml; caused an acute fall in diastolic BP (-12%, P less than 0.001) and a hemoconcentration (hematocrit +7%, P less than 0.01) not fully explained by a negative body fluid balance; increased GFR (+15%, P less than 0.05) despite unchanged or decreased ERPF (filtration fraction +37%, P less than 0.001); augmented (P less than 0.05- less than 0.001) urinary chloride (+317%), sodium (+224%), calcium (+158%), magnesium (+110%), phosphate excretion (+88%), and free water clearance (from -0.76 to +2.23 ml/min, P less than 0.001) with only little change in potassium excretion; and increased plasma norepinephrine (P less than 0.001) while plasma and urinary epinephrine and dopamine, and plasma ADH, angiotensin II, and aldosterone levels were unchanged. The magnitude and pattern of electrolyte and water excretion during alpha hANP infusion could not be accounted for by increased GFR alone. Therefore, in normal man, endogenous alpha hANP seems to circulate in blood. alpha hANP can cause a BP reduction and hemoconcentration which occur, at least in part, independently of diuresis and are accompanied by sympathetic activation. An increase in GFR that occurs in the presence of unchanged or even decreased total renal blood flow is an important but not sole mechanism of natriuresis and diuresis induced by alpha hANP in man.

Effect of atrial natriuretic factor on central angiotensin II-induced responses in rats

The effect of intracerebroventricular (ICV) injection of atrial natriuretic factor (ANF) on drinking and pressor responses induced by centrally administered angiotensin II (AII) was examined in the rat. The ICV injection of ANF attenuated water intake induced by AII or 48-hr water deprivation. In contrast, ANF did not affect AII-induced pressor responses. The ICV injection of ANF did not cause recognizable change in blood pressure in spontaneously hypertensive rats or Wistar-Kyoto rats. These results suggested that ANF in the brain is involved in the central control of water intake. Brain ANF may be considered as a selective antagonist of the dipsogenic effect of AII but not its pressor effect.

Regulatory role of atrial natriuretic polypeptide in water drinking in rats

Intracerebroventricular (i.c.v.) administration of synthetic alpha-human atrial natriuretic polypeptide (alpha-hANP) decreased the water intake of dehydrated rats. Anti-ANP antiserum, which can neutralize endogenous ANP, potentiated the water intake induced by water deprivation or angiotensin II (AII) injection in rats. These findings suggest that endogenous ANP in rat brain antagonizes the action of AII and plays an important role in the maintenance of drinking behavior.

Distribution of immunoreactive atrial natriuretic peptides in the central nervous system of the rat

The distribution of immunoreactive (ir) atrial natriuretic peptides (ANPs) in 47 microdissected brain and spinal cord regions of the rat was determined by radioimmunoassay. The highest concentrations of ir-ANPs exist in the paraventricular nucleus and median preoptic nucleus (580.9 and 558.0 fmol/mg protein, respectively). High concentrations of ir-ANP (greater than 300 fmol/mg protein) are present in the interpeduncular nucleus, preoptic and hypothalamic periventricular nuclei, median eminence and organum vasculosum of the lamina terminalis. Moderate concentrations of ir-ANPs (between 100 and 300 fmol/mg protein) are found in 16 brain regions such as the bed nucleus of the stria terminalis, nucleus of the diagonal band, most of the hypothalamic nuclei, central gray, locus coeruleus and parabrachial nuclei. Low levels of ir-ANPs (less than 100 fmol/mg protein) exist in 22 brain regions including cortical areas, amygdala, caudate nucleus, nucleus accumbens, hippocampus, supraoptic nucleus, subfornical organ, medial mammillary nucleus, substantia nigra, dorsal raphe nucleus, cerebellum, nucleus of the solitary tract and others. Cervical spinal cord and neurointermediate lobe of pituitary gland contain low levels of ir-ANPs.

Atrial natriuretic factor does not affect basal, forskolin- and CRF-stimulated adenylate cyclase activity, cAMP formation or ACTH secretion, but does stimulate cGMP synthesis in anterior pituitary

The report that ANF inhibits basal and CRF-stimulated adenylate cyclase activity in anterior pituitary homogenates suggested that the atrial peptide could inhibit ACTH secretion. This possibility was investigated in the ACTH-secreting AtT-20 mouse pituitary tumor cell line as well as homogenates or primary cell cultures from rat anterior hypophysis. ANF (up to 5 X 10(-7) M) was found to be completely ineffective in stimulating basal, CRF- and/or forskolin-stimulated adenylate cyclase activity, cAMP accumulation and ACTH secretion. Similarly, ANF had no effect on spontaneous or GRF-induced GH release from cells in primary culture. ANF receptors, however, are present in AtT-20 cells and anterior pituitary cells as evidenced by the ability of the peptide to stimulate intracellular cGMP accumulation. The data, therefore, suggests that ANF does not have a negative modulatory action on the secretory function of anterior pituitary. The role of cGMP in any other action(s) of ANF remains unknown.

ANF stimulation of detergent-dispersed particulate guanylate cyclase from bovine adrenal cortex

Particulate guanylate cyclase from bovine adrenal cortex can be stimulated by ANF. A 2-fold stimulation of the enzyme was obtained with 100 nM ANF and a half-maximal stimulation, with a 5 nM dose. The stimulation by ANF persisted for at least 30 min. Various detergents, such as Triton X-100, Lubrol PX, cholate, CHAPS, digitonin and zwittergent, stimulated several-fold the activity of particulate guanylate cyclase. However, only Triton X-100 dispersed particulate guanylate cyclase without affecting its response to ANF. The dose-response curve of ANF stimulation of the particulate and the Triton X-100 dispersed enzyme was similar. The dispersion of a fully responsive guanylate cyclase to ANF will help us to uncover the type of interactions between guanylate cyclase and ANF. It will also be used as a first step for the purification of an ANF-sensitive particulate guanylate cyclase.

Alpha-human atrial natriuretic polypeptide-induced rise of plasma and urinary cyclic 3'5'-guanosine monophosphate concentration in human subjects

Synthetic alpha-hANP was infused into 8 normotensive, euvolemic volunteers to examine the effects on plasma and urinary cyclic-GMP. The dose given and duration of alpha-hANP (0.1 micrograms/kg/min, 20 min) led to the significant diuresis, saliuresis and hypotensive effects in each subject. The mean plasma cyclic-GMP concentration was clearly elevated at 5 min after infusion and attained 8 fold of the mean basal concentrations by the end of infusion. The mean urinary cyclic-GMP excretion rate also showed 3.5 fold increases of the basal excretion rate with synthetic alpha-hANP administration (before loading: 0.69 +/- 0.22 p moles/g creat., after loading: 2.85 +/- 0.28 p moles/g creat.). However, there was no apparent change on plasma or urinary cyclic-AMP during the infusion. The result clearly demonstrated that synthetic alpha-hANP selectively induces the cyclic-GMP in concomitant with the marked diuretic, natriuretic and hypotensive effects in human subjects.

Effect of chronic infusion of atrial natriuretic factor on plasma and urinary aldosterone, plasma renin activity, blood pressure and sodium excretion in 2-K, 1-C hypertensive rats

Conscious two-kidney, one-clip (2-K, 1-C) hypertensive rats and their normotensive sham-operated controls were infused during 13 days with synthetic ANF (Arg 101 - Tyr 126) at 35 pmol/hr/rat by means of osmotic minipumps connected to the jugular vein. The initial blood pressure of 186 +/- 6 mmHg maximally decreased to 118 +/- 7 mmHg at day 5 and slowly rose afterwards without reaching basal values. A concomitant drop in pressure natriuresis and diuresis was observed. No changes were observed in ANF-infused sham-operated rats. Urinary aldosterone excretion declined in ANF-treated rats from a basal value of 63.38 +/- 21.04 micrograms/24 hr to 13.36 +/- 3.78 micrograms/24 hr the last infusion day. No change in urinary aldosterone was observed in either non-infused 2-K, 1-C or ANF-infused sham-operated rats. Plasma aldosterone was significantly higher only in non-treated 2-K, 1-C rats. Renal aldosterone clearance was significantly lower in ANF-infused 2-K, 1-C rats than in the other experimental groups. Plasma renin activity (PRA) was lower in treated (3.92 +/- 2.26 AI ng/ml/hr) than in non-treated (9.08 +/- 2.32 AI ng/ml/hr) hypertensive rats, and not different from ANF-infused or non-infused sham-operated rats. No differences in body weight between infused and non-infused rats, or hematocrit between any group were observed. Atrial immunoreactive ANF was not different in any group. These results demonstrate that chronic administration of ANF not only reduces blood pressure and PRA in 2-K, 1-C hypertensive rats but also plasma and urinary aldosterone. Whether the latter is a direct inhibitory effect or secondary to the normalization of PRA is not known. The hypotensive response may be due to a direct effect on vascular smooth muscle but a role of renin cannot be excluded. Because blood pressure returned toward basal values during the last days of the observation period, the possibility of a tachyphylactic effect of ANF on vascular smooth muscle cannot be excluded.

The inhibition of progesterone secretion and the regulation of cyclic nucleotides by atrial natriuretic factor in gonadotropin responsive murine Leydig tumor cells

We have found that atrial natriuretic factor (ANF) has a profound effect on testicular cells in altering intracellular cyclic nucleotide levels as well as progesterone secretion. Using clonal cultured Leydig tumor cells we found that 1 X 10(-8)M ANF caused a two thousand-fold elevation in the accumulation of cellular cGMP and inhibited cAMP in treated cells by more than 90% as compared to the controls. ANF (1 X 10(-8)M) also significantly inhibited gonadotropin-stimulated accumulation of cAMP in response to bovine luteinizing hormone (bLH) or human chorionic gonadotropin (hCG). Gonadotropin-stimulated progesterone secretion was inhibited by ANF (1 X 10(-10) - 1 X 10(-9)M) in these cultured Leydig tumor cells. Approximately 50% inhibition of progesterone secretion was observed at the peptide concentration of 1 X 10(-9) M.

Distribution of atrial natriuretic factor-like immunoreactive neurons in the rat brain

Using antisera generated in rabbits against rat atriopeptin III [alpha-rANP(5-28)] and human alpha-atrial natriuretic polypeptide we mapped the distribution of atrial natriuretic factor-like immunoreactivity throughout the rat central nervous system. Cell bodies were observed in the telencephalon (nucleus interstitialis striae terminalis and between the amygdala centralis and medialis), throughout the diencephalon in all nuclei of the "anteroventral third ventricle", the base of the hypothalamus, the subzona incerta area, the medial forebrain bundle and the medial habenula, in the mesencephalon (mamillary body, substantia nigra lateralis, dorsal and ventral parabrachial nuclei) and very sparse in the medulla oblongata along the fourth ventricle towards the vestibular nuclei, the nucleus tractus solitarii and nervi trigemini. Fibers were present wherever cell bodies were located. The highest relative densities were observed in the anteroventral third ventricle area and the medial habenula. Sparse fibers were also seen in the spinal cord (dorsal and ventral horn and around the central canal) and in the posterior pituitary. The predominance of the atrial natriuretic factor-like perikarya and fibers in the anteroventral third ventricle area suggests an involvement of this peptide in central blood pressure control.

Atrial natriuretic hormone, the renin-aldosterone axis, and blood pressure-electrolyte homeostasis

The renin-angiotensin-aldosterone axis exerts major control over sodium and potassium balance and arterial blood pressure. These three functions are continuously regulated by changes in angiotensin II and aldosterone levels in response to wide variations in dietary intake of sodium and potassium. In addition, changes in intrarenal physical factors cause changes in the supply of distal tubular sodium that, in turn, work to determine sodium and potassium excretion and to modulate the release of renal renin. However, certain aspects of sodium homeostasis cannot be fully explained either by the activity of the renin system or by intrarenal physical factors, and this has led investigators to search for other natriuretic hormonal mechanisms. Recently, it has become clear that atrial tissue contains a group of peptides, at least one of which is probably secreted as a regulatory hormone. In animals, these atrial peptides produce immediate, marked natriuresis associated with a rise in glomerular filtration rate (but no alteration of total renal flow) and a simultaneous decrease in arterial blood pressure. Atrial peptides also inhibit renal renin secretion and adrenal cortical secretion of aldosterone, and they oppose the vasoconstrictive action of angiotensin II. One of these atrial peptides may therefore be the long-sought natriuretic hormone, though in a different form and shape than was envisioned. The fact that atrial peptide works to oppose the renin system at four points suggests that this new hormone could have a major complementary role in long-term regulation of blood pressure and electrolyte homeostasis. In this construction the renin system primarily defends sodium balance and blood pressure, with the atrial hormone having an increasing counter-influence in situations involving high blood pressure or sodium surfeit. We can soon expect to learn more about this atrial hormone, including which peptide is the active circulating hormone, what induces or inhibits its release, and what part it plays in cardiovascular diseases.

Antisera to atrial natriuretic factor reduces urinary sodium excretion and increases plasma renin activity in rats

Although the presence of atrial natriuretic factor in the blood has been demonstrated by radioimmunoassay, its biological activity and physiological significance has not been elucidated. Using specific antiserum against atrial natriuretic factor, we investigated the effect of passive immunization in rats. A significant reduction of urine output and urinary sodium excretion lasted for about 30 min after intravenous administration of antiserum. The effects were more pronounced in rats pretreated with deoxycorticosterone acetate and saline. Plasma renin activity was increased after the administration of antiserum. No significant effects on the urinary sodium excretion was observed following injection of normal rabbit serum. The results of this study provide evidence indicating that endogenous atrial natriuretic factor plays an important role in the regulation of urinary water and sodium excretion and plasma renin activity.

Atrial natriuretic factor inhibits vasopressin secretion from rat posterior pituitary

The effects of synthetic atrial natriuretic factor (ANF) were studied in superfused rat posterior pituitary gland. ANF (10(-6)M, 10(-10)M) significantly inhibited basal as well as KC1 (50 mM) or angiotensin II-stimulated immunoreactive arginine vasopressin secretion. The magnitude of inhibition was greater at 10(-6)M than at 10(-10)M. ANF also decreased cAMP secretion and increased cGMP secretion from the posterior pituitary. These results suggest that ANF directly acts on the posterior pituitary to inhibit arginine vasopressin secretion and that this effect is, at least, partly mediated by the changes in cyclic nucleotide production.

Atrial natriuretic factor: a hormone produced by the heart

Systematic studies on the significance of the secretory-like morphological characteristic of cardiac atrial muscle cells of mammals led to the finding that these cells produce a polypeptide hormone. This hormone, described in 1981 as atrial natriuretic factor (ANF), is diuretic (natriuretic), hypotensive, and has an inhibitory effect on renin and aldosterone secretion. Thus, ANF probably intervenes in the short- and long-term control of water and electrolyte balance and of blood pressure. Phylogenetically, ANF appears early, suggesting different functions for this peptide in accordance with each species' environment. Knowledge of the properties of the hormone should provide insights into the pathophysiology of important clinical entities and lead to the development of new pharmaceutical products.

Atrial natriuretic factor inhibits the early pathway of steroid biosynthesis in bovine adrenal cortex

We have previously determined that atrial natriuretic factor (ANF) is a potent inhibitor of steroid secretion in cultured bovine zona glomerulosa and fasciculata cells. The present report describes a comparison of the effect produced by ANF on aldosterone, deoxycorticosterone and progesterone secretions by zona glomerulosa cells and on cortisol, corticosterone and progesterone secretions by zona fasciculata cells. The equipotent inhibitory action of ANF on the stimulated secretion of these steroids in both cell types indicates a common site of action prior to progesterone synthesis at which ANF inhibits the steroidogenic pathway.

Effect of atrial peptides on aldosterone production

This study examines the effects of the synthetic atrial peptides (atriopeptin I, II, and III) on aldosterone and corticosterone production by rat adrenal cell suspensions. Furthermore, we studied the effect of atriopeptin II infusion on the plasma aldosterone response to angiotensin II in the rat in vivo. Atriopeptin I, II, and III decreased aldosterone release from zona glomerulosa cells in a dose-dependent fashion. 10 pM atriopeptin II inhibited basal aldosterone release significantly (P less than 0.01), and 10 nM atriopeptin II or III lowered it by 79%. Atriopeptin II decreased the sensitivity of the glomerulosa cells to adrenocorticotropic hormone (ACTH) and angiotensin II. Atriopeptin II had no effect on basal or ACTH-stimulated corticosterone release by fasciculata-medullary cells. In vivo infusions of angiotensin II with or without simultaneous infusions of atriopeptin II showed that atriopeptin II significantly inhibited the aldosterone response to angiotensin II. This inhibition by atriopeptin II was independent of any effect on plasma renin activity, serum potassium, or ACTH. These data raise the possibility that the atrial natriuretic peptides may affect sodium excretion by the kidney, not only directly, but also indirectly through the inhibition of aldosterone production.

Rat atrial natriuretic polypeptide stimulation of adrenal zona glomerulosa cell growth

Rat atrial natriuretic polypeptide (rANP) was found to stimulate [3H] thymidine incorporation into the DNA of bovine adrenal glomerulosa cells in a primary culture in a dose-dependent manner. The minimum effective dose was a very low concentration (10(-12) M of ANP), suggesting that ANP had a physiological effect. These findings are the first indication that ANP possesses growth-stimulating activity with regard to adrenal zona glomerulosa cells.

The relationship between tissue preparation and function; methods for the study of control of aldosterone secretion: a review

The study of the control of aldosterone synthesis and secretion by the rat adrenal gland has over the past thirty years involved the application of many different in vivo and in vitro techniques. In this review the relationship between the data that each of these methods has produced is compared. There are striking differences in overall steroid production rates, and in the qualitative nature of the steroid profile which the various methods produce. In particular, aldosterone is secreted at higher rates in vivo, and when whole tissue preparations are used in vitro, than in incubations of isolated glomerulosa cells. In addition, while corticosterone is a major product of glomerulosa tissue in vitro, the available evidence suggests that it is not a major glomerulosa product in vivo.