Effect of atrial natriuretic factor on plasma vasopressin in conscious rats

An intravenous (IV) bolus injection (10 μg) of synthetic rat atrial natriuretic factor [ANF (Arg 101-Tyr 126)] into normal conscious Sprague-Dawley rats produced a significant decrease of plasma arginine vasopressin (AVP) while 1-, 2-, and 5-μg doses exerted no such effect. Mean arterial blood pressure (MAP) was lowered about 15 mmHg by an IV 10 μg bolus injection of ANF. When plasma AVP rose significantly in rats exposed to such osmotic stimuli as 600 mM NaCl and 900 mM mannitol intraperitoneally (IP), subsequent IV injection of ANF (10 μg) markedly depressed this parameter. Lower doses of ANF were ineffective against 600 mM NaCl IP. The significant elevation of plasma AVP levels by hypertonic sucrose 900 mM IP was not modified by ANF (10 μg). Blood pressure remained unchanged after IP administration of various osmotic stimuli, except mannitol, and in all these experiments an IV bolus of ANF exerted a lowering effect on MAP. Seventy-two hr water deprivation (mixed osmotic and volume stimulus) resulted in elevated plasma AVP levels which were unaffected by an IV bolus injection of ANF at doses of 0.06–10 μg. Immunoreactive ANF (IR-ANF) rose in plasma to 39.3±13 ng/ml 1 min after an IV bolus injection of 10 μg ANF, dropping to 1.01±0.2 ng/ml after 5 min and to 0.32±0.01 ng/ml after 10 min (when ANF and AVP interactions were studied), but still remained approximately six times higher than in control rats. These results suggest that, in the conscious rat, only pharmacological levels of ANF observed after an IV bolus infusion may influence both resting and osmotically-stimulated AVP levels.     

Effect of prolonged high salt diet on atrial natriuretic factor in rats

Normotensive Sprague-Dawley rats were given 8% NaCl for 5 weeks. This salt load did not affect their blood pressure nor hematocrit, and plasma atrial natriuretic factor (ANF) showed no change at 3 weeks but decreased after 5 weeks of the experimental period when compared with control rats. The responsiveness of particulate guanylate cyclase and formation of cGMP in ANF target organs suggested an augmented baseline activity of the cGMP system but its relative hyporesponsiveness to exogenous ANF following prolonged salt loading. Decreased plasma ANF levels cannot be explained by its altered production since atrial levels of the peptide were comparable in rats with or without salt loading. Atrial ANF mRNA was unaffected by the salt regimen. This study demonstrates that plasma ANF does not increase during long-term NaCl loading and even decreases after 5 weeks of 8% NaCl. The changes in plasma ANF are associated with changes in the functional state of ANF receptors coupled to particulate guanylate cyclase, but in the opposite direction than expected from lowered plasma ANF. Thus, ANF may not play a significant role in the regulation of sodium excretion in response to prolonged high salt consumption or, if it does, it is not reflected by expected changes in its plasma levels.     

A diurnal plasma vasopressin rhythm in rats

The purpose of this paper was to determine whether there is a diurnal plasma arginine vasopressin (AVP) rhythm in rats. Using an AVP radioimmunoassay, plasma AVP levels were determined at frequent intervals throughout a 24-hour period in adult male rats. Our data revealed a diurnal rhythm in plasma AVP levels, with mid-afternoon and early evening levels significantly greater than those in the morning and late evening.     

The role of posture on the changes in plasma atrial natriuretic factor and arginine vasopressin levels during immersion

In seven healthy male volunteers we investigated changes in plasma atrial natriuretic factor [( ANF]), arginine vasopressin [( AVP]) and plasma volume (PV) during supine immersion. Twenty minutes head-out water immersion in a supine position in a thermo-neutral water bath attenuated the increase in PV induced by 20 min in a supine position in air, but increased the mean plasma [ANF] from 32.0 pg.ml-1, SEM 5.1 to 53.3 pg.ml-1, SEM 3.6 and decreased the mean plasma [AVP] from 1.4 pg.ml-1, SEM 0.1 to 0.9 pg.ml-1, SEM 0.04. Simultaneously, diuresis and natriuresis increased markedly. During a 20-min control period in the supine posture without immersion, PV, plasma [ANF] and [AVP] remained unaffected while diuresis and natriuresis did not increase to the same extent. These data suggest that an increase in the central blood volume induced by a weak external hydrostatic pressure during supine immersion triggered the changes in plasma [ANF] and [AVP] and that the increase was probably due to a shift of blood volume from peripheral to central vessels. The changes in plasma [ANF] contributed to the changes in natriuresis.     

Atrial natriuretic factor inhibits vasopressin secretion in conscious sheep

To test the hypothesis that atrial natriuretic factor (ANF) has a centrally mediated action on body fluid homeostasis, the effects of intracerebroventricularly (ICV) infused ANF on plasma vasopressin (AVP) concentration and urinary water and electrolyte excretion were investigated in euhydrated and water-deprived conscious sheep. ICV ANF decreased plasma AVP concentration and increased urinary free water excretion in euhydrated sheep, with excretion of Na and K unaltered. However, ICV ANF did not affect urinary volume, free water clearance, or excretion of Na and K in dehydrated animals, although plasma AVP concentration was significantly decreased. The relationship between urine volume and plasma AVP concentration was fitted by a power curve: urine volume = 0.79 X [AVP]-0.71; urine volume changes very little as a function of AVP concentration at the higher ranges. Intravenous infusion of the same amount of ANF was without effect on plasma AVP concentration or urinary excretion in both euhydrated and dehydrated animals. Mean arterial pressure was unchanged throughout all experiments. These results are consistent with the hypothesis that central ANF inhibits AVP secretion.     

Characterization of a long-acting recombinant human serum albumin-atrial natriuretic factor (ANF) expressed in Pichia pastoris

The cardiac hormone atrial natriuretic factor (ANF) combines pharmacological properties of drugs used to treat essential hypertension (EH), congestive heart failure (CHF) and acute myocardial infarction (AMI). Treatment of CHF or AMI patients with an intravenous (iv) infusion of the circulating form of ANF (ANF(99-126)) produces significant clinical improvement. The short half-life (5 min) and peptide nature of ANF impose logistic restrictions for chronic administration. To increase its half-life, we fused ANF and human serum albumin (HSA) mini-genes by recombination in Pichia pastoris. The activity of three configurations of the fusion protein was tested in vitro and in vivo. The fusion protein that comprised of C-terminus HSA connected to N-terminus ANF via a hexaglycine linker showed the best outcome; it increased cGMP production in vitro. In vivo an iv bolus of HSA-ANF into mice increased significantly plasma cGMP levels and lowered blood pressure (BP) for up to 6 h hence successfully extended ANF half-life in plasma while retaining its biological activity. HSA-ANF represents the basis for development in the chronic therapeutic use of ANF.     

Effect of moderate hypoxemia on atrial natriuretic factor and arginine vasopressin in normal man

The object of this study was to assess the effect of moderate acute hypoxemia on plasma concentrations of atrial natriuretic factor (ANF), arginine vasopressin (AVP), plasma renin activity (PRA) and urinary excretion of prostaglandin E2 (UPGE2V). Eight volunteers were exposed for 2 hours to a gas mixture containing 10% O2, 4.5% CO2 and 85.5% N2. Hypoxia increased diastolic blood pressure and free water clearance. Hypoxia did not change the AVP, PRA or UPG2V, although increased ANF from 17.7 +/- 3.4 pg/mL to 27.2 +/- 1.7 pg/mL (p less than 0.005) at 120 minutes. ANF changes were closely associated with the rise in blood pressure.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Effects of clonidine and dihydralazine on atrial natriuretic factor and cGMP in humans

The effects of a 1-wk treatment with clonidine (75 micrograms/day twice a day) and dihydralazine (25 mg/day twice a day) on base-line levels of plasma atrial natriuretic factor (ANF) and plasma and urinary guanosine 3',5'-cyclic monophosphate (cGMP) and their changes by acute saline infusion (2 liters) in eight normal subjects were evaluated. Basal ANF was decreased to 65% in the clonidine group compared with both the control and dihydralazine groups. Volume loading increased plasma ANF levels by 30-40% of base-line values in the control and the dihydralazine groups and by 15% in the clonidine group. Basal plasma and urinary cGMP levels were raised by 30 and 90% in the dihydralazine group compared with both other groups. Volume loading increased plasma cGMP levels by 40% in the control and clonidine-treated groups and by 25% in the dihydralazine-treated group. It is concluded that ANF may contribute to hemodynamic effects of clonidine but not to those of dihydralazine. Dihydralazine increases plasma and urinary cGMP, supposedly by direct activation of the soluble guanylate cyclase.     

Hormonal responses to exercise during moderate cold exposure in young vs. middle-age subjects.

The influence of moderate cold exposure on the hormonal responses of atrial natriuretic factor (ANF), arginine vasopressin (AVP), catecholamines, and plasma renin activity (PRA) after exhaustive exercise was studied in 9 young and 10 middle-aged subjects. Exercise tests were randomly performed in temperate (30 degrees C) and cold (10 degrees C) environments. Heart rate, oxygen consumption, and peripheral arterial blood pressure were measured at regular intervals. Blood samples were collected before and immediately after exercise at 30 or 10 degrees C. Plasma sodium and potassium concentrations as well as hemoglobin and hematocrit were measured, and the change in plasma volume was calculated. At rest and during exercise, oxygen consumption was similar during exposure to both temperate and cold temperatures. During submaximal exercise intensities, the rise in heart rate was blunted while the increase in systolic blood pressure was significantly greater at 10 than at 30 degrees C. The increases in plasma sodium and potassium concentrations after exhaustion were similar between environments, as was the decrease in plasma volume. In both groups, all plasma hormones were significantly elevated postexercise, with the AVP response similar at 10 and 30 degrees C. However, the norepinephrine and ANF responses were significantly greater while the PRA response was significantly reduced at 10 degrees C. In the middle-aged subjects the epinephrine response to exercise was higher at 10 than at 30 degrees C. The greater ANF and reduced PRA responses to exercise in the cold may have resulted from central hemodynamic changes caused by cold-induced cutaneous vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

The increase of cGMP by atrial natriuretic factor correlates with the distribution of particulate guanylate cyclase

We have demonstrated previously that atrial natriuretic factor (ANF) augments urinary, plasma and kidney cGMP levels but has no significant effect upon cAMP. Using cGMP as a marker, we searched for specific target sites involved in the action of ANF in the dog kidney, and observed no change of cGMP in the proximal tubules, a 2-fold increase over basal levels in the thick loop of Henle and a 3-fold elevation in the collecting duct. The most striking action on cGMP occurred in the glomeruli with a rise of up to 50-fold being evident at 1-2 min. after the addition of ANF. The results obtained in the absence or presence of a phosphodiesterase inhibitor support the notion that the effects of ANF were exerted at the level of guanylate cyclase stimulation rather than cGMP phosphodiesterase inhibition. The action of sodium nitroprusside (SNP), a direct stimulator of soluble guanylate cyclase, differed from that of ANF. The ability of the factor to enhance cGMP levels was correlated with the distribution of particulate guanylate cyclase. This study identifies the glomeruli and the distal part of the nephron as specific targets of ANF and implicates particulate guanylate cyclase as the enzyme targetted for the expression of its action.     

Arginine vasopressin infusion increases plasma levels of atrial natriuretic factor in humans.

Seven normal subjects underwent sequential 20-min infusion of arginine vasopressin (AVP) at 0.5 and 2 ng/(kg.min) and a complete right-side heart hemodynamic evaluation during the study to analyze the effect of this hormone on atrial natriuretic factor (ANF) secretion in humans and to elucidate whether this effect was primary or secondary to the hemodynamic or hormonal changes induced by AVP. Plasma ANF levels increased at the end of the first (P less than 0.05) and second (P less than 0.01) infusion periods. No significant changes in mean arterial, pulmonary artery, right and left atrial pressures were recorded during the study. Cardiac output (P less than 0.05) and heart rate (P less than 0.05) decreased, while total vascular resistances (P less than 0.05) increased with respect to basal values in both infusion periods. Plasma renin activity decreased (P less than 0.01) at the end of the infusion, while plasma aldosterone, epinephrine and norepinephrine showed no significant changes. We conclude that arginine vasopressin increases plasma ANF levels in humans and that this effect cannot be ascribed to hemodynamic or hormonal changes induced by this hormone, suggesting a direct effect of vasopressin on the atrial myocyte.     

Circadian Rhythm of Prohormone Atrial Natriuretic Peptides 1-30, 31-67 and 99-126 in Man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.     

Circadian Rhythm of Prohormone Atrial Natriuretic Peptides 1-30, 31-67 and 99-126 in Man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.     

Atrial natriuretic factor: radioimmunoassay and effects on adrenal and pituitary glands

A simple and sensitive radioimmunoassay was developed for measurement of immunoreactive atrial natriuretic factor (IR-ANF) in rat and human plasma and in rat atria. The two atria contain about 20 micrograms ANF per rat. The right atrium contained 2.5 times more ANF than did the left. Ether anesthesia and morphine markedly increased IR-ANF in rat plasma. The concentration of IR-ANF in plasma of clinically normal human subjects was 65.3 +/- 2.5 pg/ml. Paroxysmal tachycardia and rapid atrial pacing significantly increased IR-ANF in human plasma. Two- to seven-fold higher concentrations were found in coronary sinus blood than in the peripheral circulation. In the plasma of rats and humans, circulating ANF is probably a small-molecular-weight peptide. ANF acts on the adrenal and the pituitary. ANF inhibits aldosterone secretion from rat zona glomerulosa and steroid secretion by bovine adrenal zona glomerulosa and fasciculata. ANF stimulated the basal secretion of arginine vasopressin (AVP) in vitro and inhibited KCl-stimulated release of AVP.     

Biochemical mechanisms of atrial natriuretic factor action

Since atrial natriuretic factor (ANF) is a natriuretic and vasodilatory hormone, its mechanisms of action expectedly involve so-called negative pathways of cell stimulation, notably cyclic nucleotides. Indeed, the guanylate cyclase-cyclic GMP (cGMP) system appears to be the principal mediator of ANF's action. Specifically, particulate guanylate cyclase, a membrane glycoprotein, transmits ANF's effects, as opposed to the activation of soluble guanylate cyclase such agents as sodium nitroprusside. The stimulation of particulate guanylate cyclase by ANF manifests several characteristics. One of them is the functional irreversibility of stimulation with its apparent physiological consequences: the extended impact of ANF on diuresis and vasodilation in vivo lasts beyond the duration of increased plasma ANF levels and is accompanied by a prolonged elevation of cGMP. Another characteristic is the parallelism between guanylate cyclase stimulation and increases of cGMP in extracellular fluids. cGMP egression appears to be an active process, yet its physiological implications remain to be uncovered. In heart failure, cGMP continues to reflect augmented ANF levels, suggesting that in this disease, the lack of an ANF effect on sodium excretion is due to a defect distal to cGMP generation. In hypertension, where ANF levels are either normal or slightly elevated, probably secondary to high blood pressure, the ANF responsiveness of the particulate guanylate cyclase-cGMP system, the hypotensive effects, diuresis and natriuresis are exaggerated. The implications of this exaggerated responsiveness of the ANF-cGMP system in the pathophysiology of hypertension and its potential therapeutic connotations remain to be evaluated.     

Hypothalamic action of atrial natriuretic factor to inhibit vasopressin secretion

The ability of synthetic atrial natriuretic factor (ANF) to inhibit vasopressin (AVP) release, as well as its action to inhibit water intake and salt preference in the rat, suggest a role for the peptide in the hypothalamic control of fluid volume in addition to its established actions in the kidney. We report here evidence for a direct, hypothalamic site of action of ANF to inhibit, specifically, AVP secretion. Third cerebroventricular infusion of 1.0 (p less than 0.05) and 2.0 (p less than 0.025) nmoles ANF significantly inhibited AVP release in euvolemic, normally hydrated rats while IV doses of ANF failed to significantly alter AVP release except when 5 nmoles (p less than 0.05) were infused. No significant effects on oxytocin (OT) release were observed. Vasopressin release from median eminence or pituitary, neural lobe explants during static, in vitro incubations was not significantly altered by doses of ANF ranging from 10(-12) to 10(-7) molar. Release of AVP during perifusion of neural lobe explants in the presence of ANF was similarly unaffected. However, AVP and not OT release from hypothalamo-neurohypophysial system explants was significantly inhibited in the presence of 10(-8) and 10(-7) M ANF, suggesting an action of the peptide at the levels of the AVP-producing cell bodies in the included supraoptic nucleus either directly or via an action on an interneuron, and not at the AVP-containing terminal fields in the median eminence or neural lobe.     

Presence of atrial natriuretic factor and cyclic guanosine monophosphate in saliva. Comparison of plasma and salivary concentrations during a head-down tilt

Using a specific and sensitive radio-immunoassay involving separation and extraction procedures, we measured the concentration of saliva and plasma atrial natriuric factor (ANF) and cyclic guanosine monophosphate (cGMP) in men before and during a 10 h head-down tilt at -6 degrees. Saliva values closely correlated with plasma for ANF (r = 0.7-0.95) and for cGMP (r = 0.65-1). During this dynamic test, the mean concentrations of ANF and cGMP were significantly higher after 15 and 45 min, respectively, this increase persisting for 3.5 h. We concluded that the concentration of ANF in saliva may be significantly affected by a marked fluid shift from the lower to the upper half of the body. This is the first time that the presence of ANF and cGMP has been demonstrated in saliva. The great advantage of studying saliva is that it can be obtained non-invasively in athletes or during space flight. This methodology will be used during the Soviet-French space flight (Antares Project) planned for 1992.     

Atrial natriuretic factor-induced cGMP accumulation in rat anterior pituitary cells in culture is not coupled to hormonal secretion

While atrial natriuretic factor (ANF) does not influence ACTH secretion, it was reported to have a marked stimulatory effect on the intracellular accumulation of cGMP in rat anterior pituitary cells in culture. Since many biological actions of ANF appear coupled to its excitatory action on target cell guanylate cyclase, the current study was designed to characterize the ANF-induced cGMP response in anterior pituitary with a view to determining whether the nucleotide plays a regulatory role in the secretory function of this gland. A 3 min exposure of cells in primary culture to 300 nM ANF (99-126) or 100 microM sodium nitroprusside (SNP), a stimulator of guanylate cyclase, causes maximal 10- and 3-fold elevations of cGMP levels, respectively. Following a progressive decrease, 6- and 2-fold increases over basal cGMP levels are still observed after 180 min of incubation with ANF (99-126) and SNP, respectively. The half-maximal stimulation of cGMP accumulation induced by a 10 min exposure to ANF (99-126), or rat atriopeptin II (ANF 103-125) is observed at 9 +/- 2 and 125 +/- 22 nM, respectively. ANF fragments (99-109) and (111-126), as well as human cardiodilatin (hANF 1-16), do not alter cGMP levels. Basal and ANF-induced cGMP levels are at least 10-fold higher in cell populations enriched in gonadotrophs compared to gonadotroph-impoverished preparations. A 3 h incubation of cells with ANF (0.1-1000 nM), however, fails to modify spontaneous or LHRH-induced LH secretion. Similarly, ANF does not alter spontaneous release of GH, TSH or PRL. The data suggest indirectly that gonadotrophs represent a principal site at which ANF acts to stimulate cGMP synthesis, but that the nucleotide is not a specific regulator of the LH secretory process; nor is it generally involved as a second messenger in the secretory function of any cell type of the anterior pituitary gland.     

The blood pressure and renal responses to SCH 34826, a neutral metalloendopeptidase inhibitor, and C-ANF (4-23) in Doca-salt hypertensive rats.

C-ANF (4-23) and neutral metalloendopeptidase (NEP) inhibitors have been shown to prevent ANF metabolism and lower blood pressure presumably by the accumulation of ANF in the circulation. In the present study, we examined the interaction between C-ANF (4-23) and SCH 34826, an inhibitor of NEP, and ensuing effects on blood pressure, excretion of urine and sodium, and cGMP in the plasma and urine in conscious DOCA-salt hypertensive rats. C-ANF (100 micrograms/kg, iv bolus plus 10 micrograms/kg/min X 30) or SCH 34826 (90 mg/kg, sc) alone caused significant reductions in blood pressure and increases in plasma and urinary excretion of cGMP, a biochemical marker of endogenous ANF activity, at one hour post-drug. C-ANF (4-23) alone elicited a significant diuresis and natriuresis. SCH 34826 also enhanced sodium excretion and tended to increase urine volume. In comparison, the combination of C-ANF (4-23) and SCH 34826 produced a greater reduction in blood pressure and increases in plasma and urinary excretion of cGMP than either agent alone. The combination also caused significant diuresis and natriuresis. It is suggested that the greater blood pressure and renal responses to a combination of SCH 34826 and C-ANF than either agent alone reflect greater accumulation of endogenous ANF due to concomitant inhibition of both receptor-mediated clearance and NEP.