Inhibition of aldosterone production by an atrial extract

Effects of human atrial natriuretic polypeptide on pancreatic exocrine secretion in the dog

We examined the effects of atrial natriuretic polypeptide (hANP) on exocrine function in the isolated and blood-perfused dog pancreas in situ. Intra-arterial injection of hANP (1-10 micrograms) resulted in the dose-dependent increases of the pancreatic juice secretion. The secretory activity of 3 micrograms of hANP was approximately equal to one third of the secretory activity of 0.1 units of secretin. The use of hANP increased the concentration of bicarbonate but not that of sodium and protein in the pancreatic juice as compared with the basal values. These secretory responses to hANP were not inhibited by treatment with haloperidol, sulpiride, phentolamine, propranolol, atropine, cimetidine or ethacrynic acid. These results suggest that hANP acts directly on the pancreatic exocrine gland to stimulate pancreatic secretion; without, however, increasing sodium excretion. The mechanism of this effect remains to be elucidated.

Decreased ANF atrial content and vascular reactivity to ANF in spontaneous and renal hypertensive rats

The relationship between ANF activity and hypertension was determined by measuring ANF atrial content and vascular reactivity in two different models: spontaneous hypertensive rats (SHR) and renal hypertensive rats (RHR). Atrial extracts and aortic strips were prepared from hypertensive and normotensive animals. Relaxant activities of extracts, synthetic ANF and nitroglycerin were assayed on superfused aortic strips previously contracted by norepinephrine. ANF atrial content was statistically significantly lower in both models of hypertension, presumably by increased ANF release into the circulation which results in depletion of tissue storage sites. Vascular subsensitivity to ANF and nitroglycerin was found in both models of hypertension. Diminished ANF vascular reactivity in hypertension could be due to receptor down-regulation and/or to a decrease in the ability of cGMP to induce relaxation.

The dopamine receptor antagonist haloperidol blocks natriuretic but not hypotensive effects of the atrial natriuretic factor

Studies were performed on anesthetized male Münich-Wistar rats to investigate the influence of the dopamine (DA) receptor antagonist haloperidol on the natriuretic response to infusion of a synthetic atrial natriuretic factor. The whole kidney glomerular filtration rate (GFR), urinary excretion of electrolytes, and arterial blood pressure (BP) were therefore measured in groups of animals pretreated with haloperidol or vehicle and given a continuous intravenous infusion of atrial natriuretic peptide (ANP; 28 amino acids). Forty-five minutes of ANP infusion at 10 micrograms h-1 kg-1 body wt did not increase GFR (change from 1.14 +/- 0.08 to 1.15 +/- 0.05 ml min-1 g-1 kidney wt). Sodium excretion (UNaV) increased more than four-fold from 0.037 +/- 0.008 to 0.165 +/- 0.070 mumol min-1 g-1 kidney wt (P less than 0.01). Potassium excretion (UKV) increased by 86% (P less than 0.001) and the urine flow rate (V) increased transiently by 63% (P less than 0.05) and did not differ from the control value during the last 15 min of ANP infusion. The urinary sodium concentration (UNa) increased almost three-fold, while BP decreased by 14%. There was no change in urine osmolality. In animals pretreated with haloperidol (1 mg kg-1 body wt), 45 min of ANP infusion did not significantly alter GFR (from 1.10 +/- 0.08 to 0.98 +/- 0.09 ml min-1 g-1 kidney wt). The UNaV did not increase significantly (change from 0.026 +/- 0.006 to 0.030 +/- 0.009 mumol min-1 g-1 kidney wt). The UKV was not elevated by ANP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of atrial natriuretic peptide (ANP) during converting enzyme inhibition

Studies were performed on anesthetized adult Münich-Wistar rats to investigate the role of angiotensin II in the natriuretic response to synthetic atrial natriuretic peptide (ANP, 28 amino acids). For this purpose the whole kidney glomerular filtration rate (GFR) and urinary excretion of electrolytes were measured in groups of animals pretreated with the converting enzyme inhibitor captopril (3 mg h-1 kg-1 body wt) or vehicle and then given a continuous intravenous infusion of ANP at 10 micrograms h-1 kg-1 body wt. In the vehicle-pretreated animals, 45 min of ANP infusion did not change GFR (control value 1.17 +/- 0.11, experimental value 1.17 +/- 0.06 ml min-1 g-1 kidney wt). Sodium excretion (UNaV) increased more than three-fold from 0.036 +/- 0.010 to 0.134 +/- 0.058 mumol min-1 g-1 kidney wt (p less than 0.05) and potassium excretion (UKV) increased from 0.481 +/- 0.055 to 0.946 +/- 0.068 mumol min-1 g-1 kidney wt (P less than 0.05). Urine osmolality (UOsm) remained unchanged, while the blood pressure (BP) decreased by 15%. In animals pretreated with captopril, ANP infusion led to a decrease in GFR from 1.27 +/- 0.11 to 1.05 +/- 0.09 ml min-1 g-1 kidney wt (P less than 0.05). Despite this effect, UNaV increased more than two-fold from 0.076 +/- 0.020 to 0.193 +/- 0.087 mumol min-1 g-1 kidney wt (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiating effect of aldosterone on the diuretic action of atrial extract

The typical stimulatory effect of a rat heart atrial extract on urinary water, sodium, potassium and kallikrein excretion is significantly increased by a previous administration of aldosterone (0.5 microgram/100 g b. wt) in the rat.

Vagal mediation of the effects of atrial natriuretic factor on blood pressure and arterial baroreflexes in the rabbit

We investigated the hemodynamic effect of synthetic atrial natriuretic factor Auriculin A (ANF) and its influence on arterial baroreflex control of heart rate, systemic blood pressure, and perfusion pressure in the hind limb (perfused at constant flow) in rabbits anesthetized with alpha-chloralose and urethane. The neural mechanisms underlying these effects were also studied. In the intact animal, a 45-minute constant infusion of ANF (2 micrograms/kg prime, 0.2 microgram/kg/min) significantly reduced mean blood pressure and increased mean perfusion pressure, while heart rate did not change. Comparable data were obtained with lower (0.5 microgram/kg + 0.05 microgram/kg/min; 1 microgram/kg + 0.1 microgram/kg/min) or higher (4 micrograms/kg + 0.4 microgram/kg/min; 8 micrograms/kg + 0.8 microgram/kg/min) doses of ANF. In addition, ANF enhanced bradycardic reflex responses to phenylephrine i.v. bolus administration, while it did not change baroreflex-mediated responses to nitroglycerin i.v. bolus administration and to 30-second bilateral carotid occlusion. The specificity of the influence of ANF on arterial baroreflex responses was confirmed by the observation that no significant change in reflex responses to phenylephrine or carotid occlusion was detectable during a comparable decrease in blood pressure induced by a constant infusion of nitroglycerin. Bilateral vagotomy prevented both the fall in blood pressure and the increase in perfusion pressure induced by ANF, while cholinergic blockade (atropine, 0.5 mg/kg i.v.) or adrenergic blockade (propranolol, 0.3 mg/kg i.v. + phentolamine, 0.3 mg/kg i.v.) did not modify the hemodynamic response to ANF observed in the intact animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased density of vascular receptors for atrial natriuretic peptide in DOCA-salt hypertensive rats

We have previously found that vascular receptors for atrial natriuretic peptide (ANP) in the rat are down-regulated by volume expansion. For this reason vascular ANP receptor density and affinity were examined in a model of volume-expanded hypertension, the deoxycorticosterone acetate (DOCA)-salt hypertensive rat. The density of mesenteric vascular ANP binding sites was decreased in DOCA-salt hypertensive rats from a control value in uninephrectomized rats of 203 +/- 25 fmol/mg protein to 60 +/- 13 fmol/mg protein (p less than 0.01). The sensitivity of norepinephrine-precontracted aorta to ANP was significantly reduced in DOCA-salt hypertensive rats (p less than 0.001). DOCA-salt hypertensive rats infused intravenously for 4 days with ANP, 100 to 300 ng/hr, did not experience a lowering of blood pressure, in contrast to the significant reduction in blood pressure seen in two-kidney, one clip Goldblatt hypertensive rats similarly infused. In the latter there was no natriuretic response to ANP, while in the DOCA-salt hypertensive rats natriuresis occurred without lowering of blood pressure. In the DOCA-salt hypertensive rats plasma ANP concentration was increased to 68 +/- 8 fmol/ml from 10 +/- 1 fmol/ml in uninephrectomized rats. In conclusion, raised ANP concentration in plasma of volume-expanded hypertensive rats (DOCA-salt hypertension) may result in decreased density of ANP vascular receptors. These results suggest that a decrement in the number of ANP receptors may be a cause of decreased sensitivity of vascular responses to ANP in vitro and resistance to the blood pressure-lowering action of ANP in vivo.

Circulating atrial natriuretic polypeptide in essential hypertension

To investigate the significance of atrial natriuretic polypeptide (ANP) in essential hypertension, we measured plasma ANP concentrations in 43 subjects with essential hypertension uncomplicated by cardiac or renal failure, in 16 subjects with borderline hypertension, and in 17 normotensive control subjects. Plasma ANP levels were significantly higher in hypertensive subjects compared to borderline hypertensive subjects (p less than 0.05) and normotensive control subjects (p less than 0.05). Hypertensive subjects with left ventricular hypertrophy (LVH) had higher plasma ANP levels than the hypertensive group as a whole (p less than 0.05). A significant positive correlation was observed between mean blood pressure and plasma ANP level in the hypertensive group (n = 43, gamma = 0.77, p less than 0.01). Furthermore, plasma ANP level was decreased significantly after 4 weeks of effective antihypertensive therapy compared with the initial value (p less than 0.05). These results suggest that plasma ANP is frequently elevated in hypertensive subjects with markedly high blood pressure or LVH, and it can be reduced by effective therapy with antihypertensive drugs.

Plasma atrial peptide concentration during acute changes in cardiac filling pressure induced by a contrast agent

Left ventricular end-diastolic pressure and the concentration of atrial peptides in plasma were measured before and after the administration of contrast material into the left ventricle of 12 patients during cardiac catheterization. A positive relationship between changes in left ventricular end-diastolic pressure and the circulating level of atrial peptides was found in all 12 patients. Increases in plasma atrial peptide levels were detected within less than one minute after injection of the contrast agent. We conclude that the release of atrial peptides in the human is modulated rapidly by changes in atrial pressure. The rapid release of peptides from the atria in response to an increase in atrial pressure, coupled with evidence that atrial peptides reduce cardiac filling pressure, is consistent with the possibility that the atrial peptides may serve as part of a negative feedback system that enables the heart to influence its own filling pressure.

Atrial natriuretic peptide inhibits angiotensin-stimulated proximal tubular sodium and water reabsorption

The discovery that atrial extracts have potent diuretic and natriuretic properties revealed a possible endocrine function of the heart in the regulation of extracellular fluid volume. Since that first report intense research activity has been directed towards determining the mechanism of action of the active atrial natriuretic polypeptides (ANP) found in these extracts. Despite these efforts it remains controversial whether the renal actions of ANP are exerted solely on the process of glomerular filtration or involve additional direct actions on tubular transport. We have investigated the possibility that atrial natriuretic polypeptides may induce natriuresis by suppression of proximal tubular sodium and water reabsorption. Using shrinking split-drop micropuncture combined with simultaneous capillary perfusion in anaesthetized rats we report that 20 nanomolar alpha-rANP (the main component of ANP in rat plasma) added to the peritubular fluid had no direct effect on proximal fluid uptake whereas picomolar angiotensin II had a marked stimulatory action as reported. The stimulatory effect of angiotensin II on fluid reabsorption was inhibited by peritubular ANP at physiological concentrations and abolished by higher concentrations of ANP. Thus at physiological concentrations ANP acts within the kidney to decrease proximal reabsorption by inhibition of angiotensin-stimulated sodium and water transport.

The renal, cardiovascular and hormonal actions of human atrial natriuretic peptide in man; effects of indomethacin

The renal, cardiovascular and hormonal effects of intravenous infusion of alpha-human atrial natriuretic polypeptides (alpha-hANP) at the concentrations of 0.0125, 0.025, 0.05, 0.1 microgram kg-1 min-1 for 20 min was studied in six male volunteers before and after indomethacin administration (150 mg day-1, three times daily for 3 days). Dose-dependent diuresis and natriuresis were observed in all subjects between the concentrations of 0.025 and 0.1 microgram kg-1 min-1, which were not influenced by indomethacin. Diastolic blood pressure decreased significantly (P less than 0.05) at the higher dose (0.05 microgram kg-1 min-1) of alpha-hANP, which was attenuated by indomethacin pretreatment. The plasma concentration of the immunoreactive alpha-hANP was 73.7 +/- 25 pg ml-1 on the control in subjects taking 200 mEq day-1 of sodium, and significant diuresis occurred when plasma concentration reached approximately 330.5 +/- 74.4 pg ml-1. alpha-hANP infusion caused a dose-dependent increase in cyclic GMP, no significant changes in plasma aldosterone and 18-hydroxycorticosterone, which were not influenced by indomethacin pretreatment. Plasma renin did not change in response to alpha-hANP infusion, which was significantly decreased (P less than 0.05) after indomethacin pretreatment. These results support that the renal effects of alpha-hANP may be exerted by prostaglandin-independent mechanisms. The renal effects occur at lower doses, and cardiovascular changes occur at higher doses of alpha-hANP.

Complementary changes in plasma atrial natriuretic peptide and antidiuretic hormone concentrations in response to volume expansion and haemorrhage: studies in conscious normotensive and spontaneously hypertensive rats

1. Plasma concentrations of atrial natriuretic peptide (ANP) and antidiuretic hormone (ADH) were measured in conscious stroke-prone spontaneously hypertensive (SPR), spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats before and after acute volume expansion or haemorrhage. 2. Plasma ANP concentration was reduced to one-third of resting values 30 min after a 1.5% haemorrhage (1.5 ml of blood per 100 g bodyweight). Plasma ADH concentration rose immediately 50-fold on haemorrhage and remained elevated at 30 min. 3. Plasma ANP concentration increased 2.5-fold relative to resting values 1 min after infusion of 2.0 ml per 100 g 5% dextrose; after 10 min plasma ANP remained elevated. Plasma ADH concentration tended to fall on volume expansion although no significant decrease was observed. 4. There was no difference in the basal levels of ANP and ADH, or in the changes produced by alterations in blood volume, in hypertensive SPR and SHR compared with normotensive WKY. 5. Thus, plasma ANP concentrations moved in opposite directions in response to two physiological stimuli: volume expansion and haemorrhage. Reciprocal changes were observed in plasma ADH.

Role of calcium in effects of atrial natriuretic peptide on aldosterone production in adrenal glomerulosa cells

Atrial natriuretic peptide (ANP) inhibits the stimulation of aldosterone secretion by isolated adrenal glomerulosa cells produced by angiotensin II (ANG II), ACTH, and potassium. The effect of ANP on the dose-response curve of aldosterone stimulated by ANG II, ACTH, and potassium on isolated rat adrenal glomerulosa cells was studied. In the presence of ANP the maximal response of aldosterone output stimulated by ANG II or potassium decreased and the half-maximum (EC50) of the response to ACTH was displaced to the right. Because these effects resemble those of calcium-channel blockers, we investigated the effect of different concentrations of nifedipine, a dihydropyridine calcium-channel blocker, on the dose-response curve of aldosterone stimulated by ANG II, ACTH, and potassium. Nifedipine produced effects similar to ANP. The maximal response of aldosterone stimulated by ANG II and potassium was decreased and the dose-response curve to ACTH was displaced to the right. ANP decreased the maximal response of aldosterone to the dihydropyridine derivative BAY K8644, a calcium-channel "activator," without change in its EC50. In contrast, nifedipine displaced the dose-response curve to BAY K8644 to the right as expected of a competitive inhibitor. The effect of ANP and nifedipine on basal and stimulated 45Ca influx into isolated rat adrenal glomerulosa cells was studied. Basal calcium influx was not significantly affected by ANP or nifedipine. Angiotensin II-, ACTH-, potassium-, and BAY K8644-stimulated calcium influx were significantly decreased by 1 nM ANP or 30 microM nifedipine. ANP may act on the rat adrenal glomerulosa cells at least in part by interference with calcium entry.

The influence of Atriopeptins I and II on the relationship between glomerular filtration and natriuresis

The effects of two pure synthetic atrial natriuretic factors, Atriopeptin (AP) I and AP II, on the whole kidney glomerular filtration rate (GFR), sodium and potassium excretion (UNaV, UKV), urine flow rate (V) and arterial blood pressure (BP) were studied in adult male Sprague-Dawley rats. The variables were measured during a control period and during 70 min of continuous intravenous infusion of AP I or AP II at a rate of 10 micrograms h-1 kg-1 body wt. A time control group was studied in parallel to see whether the variables under study changed with time. The AP I infusion did not affect GFR (change from 1.34 +/- 0.10 to 1.24 +/- 0.04 ml min-1 g-1 kidney wt), but was clearly natriuretic (UNaV changed from 0.071 +/- 0.011 to 0.229 +/- 0.038 mumol min-1 g-1 kidney wt, P less than 0.01). The UKV increased from 0.504 +/- 0.073 to 1.138 +/- 0.121 mumol min-1 g-1 kidney wt, (P less than 0.001) and V from 1.88 +/- 0.10 to 2.94 +/- 0.15 microliter min-1 g-1 kidney wt, (P less than 0.001). Urine osmolality (Uosm) and BP were unaffected. During AP II infusion GFR remained unchanged but was slightly below the pre-infusion level during the last infusion period (1.05 +/- 0.07 as against 1.37 +/- 0.09 ml min-1 g-1 kidney wt, P less than 0.05). Despite this fact, UNaV was significantly elevated throughout the infusion period.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of increased plasma atrial natriuretic factor and renal sodium handling during immersion-induced central hypervolemia in normal humans

Although maneuvers augmenting atrial volume and/or stretch also augment plasma levels of atrial natriuretic factor (ANF), the role of ANF in modulating renal sodium and water handling has not been defined. Water immersion to the neck (NI) was employed to assess the ANF response to acute volume expansion in 13 seated sodium-replete normal subjects. ANF increased promptly and markedly from 7.8 +/- 1.8 to 19.4 +/- 3.8 fmol/ml, then declined to 6.3 +/- 1.4 fmol/ml after 60 min recovery. Concomitantly, NI increased urine flow rate (V) (2.0 +/- 0.6 to 7.0 +/- 0.9 ml/min; P less than 0.001) and sodium excretion (UNaV) (92 +/- 12 to 191 +/- 15 mu eq/min; P less than 0.001), and decreased PRA (-66 +/- 3%) and plasma aldosterone (-57 +/- 6%). Increases of plasma ANF ranged from less than 20% to over 12-fold. Similarly, the natriuretic response to NI varied markedly from none to 500%. There was a strong correlation between peak ANF and peak UNaV (r = 0.67; P less than 0.025), but none between peak V and peak plasma ANF (r = -0.10; P greater than 0.5). These findings suggest that an increase in plasma ANF contributes to the natriuretic response to NI, implying a physiological role for ANF in modulating volume homeostasis in humans.

Atrial natriuretic factor during atrial fibrillation and supraventricular tachycardia

Plasma immunoreactive atrial natriuretic factor was measured in 10 patients with chronic atrial fibrillation before and after cardioversion to sinus rhythm, and in 14 patients during electrophysiologic evaluation of paroxysmal supraventricular tachycardia. The mean plasma concentration of atrial natriuretic factor in atrial fibrillation was 138 +/- 48 pg/ml and decreased to 116 +/- 45 pg/ml 1 hour after cardioversion to sinus rhythm (p less than 0.005). The mean plasma concentration of atrial natriuretic factor increased from 117 +/- 53 pg/ml in sinus rhythm to 251 +/- 137 pg/ml during laboratory-induced supraventricular tachycardia (p less than 0.005). Right atrial pressures were recorded in 12 patients; the baseline atrial pressure was 4.3 +/- 1.9 mm Hg and increased to 7.4 +/- 3.6 mm Hg during supraventricular tachycardia (p less than 0.005). A modest but significant linear relation was noted between the changes in plasma atrial natriuretic factor and right atrial pressure measurements during induced supraventricular tachycardia (r = 0.60, p less than 0.05). In conclusion, changes in atrial rhythm and pressure may be an important factor modulating the release of atrial natriuretic factor in the circulation and raised levels of this hormone may be a contributing factor for the polyuria and the hypotension associated with paroxysmal supraventricular tachyarrhythmias.

Atrial natriuretic factor: physiologic actions and implications in congestive heart failure

Atrial natriuretic factor (ANF) represents a newly recognized hormone of cardiac origin. This peptide is synthesized by the myocardial cells of both atria and released by atrial stretch. The hormone promotes sodium and water excretion by the kidney, inhibits the renin-angiotensin-aldosterone system, and reduces systemic arterial pressure. Specific receptors for ANF are present in the kidney, adrenal glands, vascular smooth muscle, platelets and central nervous system. Congestive heart failure is characterized by increased circulating levels of ANF; however, there appears to be an attenuation in the renal response to the hormone. Recent investigations have reported the effect of systemic administration of synthetic ANF to normal individuals and those with congestive heart failure. The hormone may promote a significant natriuresis and diuresis in addition to reducing arterial pressure and inhibiting renin and aldosterone secretion. Substantial questions remain as to the full physiologic significance and therapeutic potential of this hormone.

Direct radioimmunoassay of human plasma atrial natriuretic peptide in various normal and pathophysiological states: increase in renal and cardiac failure during exercise

We have used a sensitive direct radioimmunoassay to study the effects of exercise on plasma atrial natriuretic peptide (ANP) concentrations in man. Plasma ANP concentration increased three-fold in sixteen patients undergoing bicycle ergometer electrocardiographic tests for the investigation of chest pain. Resting ANP concentrations were higher in those patients in whom there was more evidence of heart disease, such as a positive exercise test, treatment with a beta blocker or history of myocardial infarction, although exercise resulted in increased ANP in both groups. We also confirm the increased plasma ANP concentration observed in patients with congestive cardiac failure and renal failure. In nine patients with renal failure routine haemodialysis was accompanied by a 30 per cent reduction in plasma ANP concentration. Plasma ANP concentrations were similar in treated hypertensive patients, untreated borderline hypertensive patients and normotensive subjects.

Sodium excretion and atrial natriuretic peptide levels during mineralocorticoid administration. A mechanism for the escape from hyperaldosteronism

Urinary sodium excretion initially decreases when mineralocorticoid levels are increased, but if high plasma levels of hormone are maintained, sodium excretion rises to again equal sodium intake. To ascertain if atrial natriuretic peptide (ANP) plays a role in reestablishing sodium balance during mineralocorticoid ingestion, 0.3 to 0.5 mg per day of fludrocortisone were administered for 18 days to four healthy male subjects. The average daily intake of sodium was regulated at 180 +/- 2 meq. ANP levels rose from a mean of 91.7 +/- 13.0 pg/ml during the control week to 179.7 +/- 39.2 pg/ml during the final week on fludrocortisone (p less than 0.05). Urinary sodium excretion fell 27% immediately after fludrocortisone administration was initiated but returned to baseline levels in an average of 5 days. Levels of ANP, normalized for each subject to the mean of his control week values, correlated with the amount of sodium excreted in the subsequent 24 hours (p less than 0.05). Simultaneous with the rise in ANP values, levels of plasma renin activity (PRA) and aldosterone decreased. ANP concentrations throughout the study were inversely correlated with PRA and aldosterone levels (p less than 0.001 for both correlations). Values of serum osmolality and plasma arginine vasopressin did not change significantly during the study. The results obtained demonstrate that increased secretion of ANP is associated with escape from the sodium retaining effect of chronically high mineralocorticoid levels in man and suggest that ANP plays a prominent role in the mechanism of this escape.

The gene for the atrial natriuretic factor is expressed in the aortic arch

The gene for atrial natriuretic factor is expressed within the adventitial cells of the rat aortic arch. Atrial natriuretic factor transcripts, similar in overall size (1100-1200 nucleotides) and 5'-termini to those found in the atria, were identified in the arch. Much lower levels (approximately 10-20%) of these transcripts were present in distal thoracic aorta. Atrial natriuretic factor peptide was localized by immunocytochemistry to the adventitia of the arch in regions thought to harbor the aortic baroreceptors. These data suggest a previously unsuspected role for the peptide in regulating systemic blood pressure through the baroreceptor reflex.

The vasodilator potency of atrial natriuretic peptide in man

The vasodilating potency of alpha-human atrial natriuretic peptide (alpha-hANP) was investigated in the forearms of 16 normotensive subjects, 22 to 48 (mean 28) years old, with the use of venous occlusion plethysmography. alpha-hANP, 0.005 to 1.5 micrograms/min/100 ml forearm volume (FAV), infused in nine dose steps into the brachial artery increased forearm blood flow (FAF; ml/min/100 ml FAV) from 2.8 +/- 0.4 (SEM) to a maximum of 9.6 +/- 1.1. Forearm vascular resistance (mean arterial pressure/FAF) decreased by 72%. The alpha-hANP dose that produced a 50% vasodilator response was 0.093 +/- 0.016 microgram/min/100 ml FAV (n = 11) and it resulted in a venous plasma concentration of ANP (pANP) of 115 +/- 7 pmol/liter (normal 2 to 80; radioreceptor assay). Intraindividually, the maximum dose of alpha-hANP induced an increase in FAF that was 60% of the maximum response to sodium nitroprusside (14.1 +/- 1.8). Combined infusions (n = 9) of maximum forearm vasodilator doses of alpha-hANP and nitroprusside increased FAF to 22.7 +/- 3.4; this additive vasodilator effect of alpha-hANP and nitroprusside is consistent with their different actions on the guanylate cyclase system. In man, the direct vasorelaxant effect of alpha-hANP occurs at concentrations within the upper normal range of pANP, suggesting a physiologic vasodilator role for alpha-hANP.

Atrial natriuretic peptide does not affect corticotropin-releasing factor-, arginine vasopressin- and angiotensin II-induced adrenocorticotropic hormone release in vivo or in vitro

The effect of synthetic atrial natriuretic peptide (ANP) was examined on the in vivo and in vitro release of ACTH. Intravenous ANP (4 micrograms/kg body weight) administration did not affect the corticotropin releasing factor (CRF, 4 micrograms/kg body weight)-, arginine vasopressin (AVP, 2 micrograms/kg body weight)- and angiotensin II (A II, 4 micrograms/kg body weight)-induced ACTH release in unanesthetized freely moving rats. ANP did not inhibit the basal, CRF- and AVP-induced release of ACTH in pituitary cell cultures. ANP did not affect the CRF- and AVP-induced plasma corticosterone elevation, while it attenuated the AVP-induced corticosterone elevation. These results indicate that ANP does not affect the ACTH release at the pituitary level in vivo and in vitro.

Plasma atrial natriuretic peptide is increased during atrial pacing in conscious rabbits

The effect of increases in heart rate on plasma atrial natriuretic peptide (ANP) concentrations was investigated in conscious rabbits. Plasma ANP concentrations were significantly increased following abrupt increases in heart rate produced by atrial pacing at 400 beats/min. Pacing at 300 beats/min resulted in smaller increases in plasma ANP concentration. Stepwise increases in heart rate produced by atrial pacing at 250, 300, 350 and 400 beats/min resulted in increases in plasma ANP concentrations at 400 beats/min only. The increase in plasma ANP concentration during atrial pacing correlated significantly with the increase in heart rate achieved.

Alpha-h-ANP injection in normals, low renin hypertension and primary aldosteronism

Atrial natriuretic peptide, a hormone secreted by the heart, is involved in salt and fluid homeostasis and also exerts an inhibitory effect on aldosterone production in vitro. In order to elucidate if this effect is also present in man, 6 normal volunteers, 5 low renin hypertensive patients (LRH) and 7 patients with primary aldosteronism (PA) have received 100 micrograms of alpha-h-Anp as bolus i.v. (The decrease in blood pressure was mild and transient in all groups, whereas a marked diuretic effect was observed in all hypertensives even in PA where high levels of endogenous ANP have been found. In normals we observed a significant decrease of plasma aldosterone values while in PA and LRH this effect was not evident. This phenomenon associated with a greater natriuretic effect in LRH and PA, as compared with normals, demonstrates the lack of the correlation between ANP-induced diuresis and aldosterone inhibiting properties.

Renin dependency of the effect of chronically administered atrial natriuretic factor in two-kidney, one clip rats

Conscious two-kidney, one clip rats with 150 mm Hg or higher systolic blood pressure were infused with saralasin for 60 minutes. Those with a blood pressure decline of 30 mm Hg or more were classified as saralasin-sensitive; those with a decrease of 10 mm Hg or less were considered saralasin-resistant. The animals were then housed in metabolic cages. Groups of sham-operated normotensive, saralasin-sensitive or saralasin-resistant two-kidney, one clip (2K1C) rats were infused with atrial natriuretic factor (Arg 101-Tyr 126), 100 ng/hr per rat, for 6 days. Corresponding control groups were sham-infused. Blood pressure was initially higher in the saralasin-sensitive groups (176 +/- 6 and 181 +/- 1 mm Hg, respectively) than in the saralasin-resistant groups (160 +/- 4 and 169 +/- 4 mm Hg, respectively). Atrial natriuretic factor infusion produced a gradual decline in blood pressure to 128 +/- 5 mm Hg, but only in saralasin-sensitive 2K1C animals. Urinary volume, initially higher in saralasin-sensitive hypertensive than in normotensive rats, was depressed during atrial natriuretic factor infusion. Urinary sodium excretion and water intake showed the same tendency, but the changes were not significant. No such modifications were observed in saralasin-resistant or sham-operated rats infused with atrial natriuretic factor. Body weight, which was higher in normotensive animals, was unchanged during atrial natriuretic factor infusion. Saralasin-sensitive, noninfused 2K1C rats were the only group with higher plasma renin activity than sham-operated, normotensive controls. Plasma aldosterone was higher in the former than in the other five groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in adrenal responsiveness and potassium balance with shifts in sodium intake

Dietary sodium modulates the aldosterone response to angiotensin, but available evidence does not indicate whether there is a gradual change in adrenal responsiveness with intermediate sodium intakes or a sharp shift from a low to a high responsive level at some threshold sodium intake. Nine normal subjects received angiotensin II infusions while in balance on five levels of sodium intake over two orders of magnitude, 3 to 300 mEq sodium per day. Basal plasma renin activity, plasma aldosterone and plasma angiotensin II concentrations gradually fell as dietary sodium intake increased. The adrenal was quite sensitive to the state of sodium balance since a shift in sodium intake of as little as 20 mEq (e.g. 10 to 30 mEq/day) induced a significant change in basal plasma aldosterone. Adrenal responsiveness to infused angiotensin varied inversely with the log of urinary sodium excretion over the entire range of sodium intake, indicating that there is a gradual modulation of adrenal responsiveness with changes in dietary sodium. In addition, despite a constant dietary potassium intake, serum potassium gradually fell from 4.55 +/- .06 to 3.98 +/- .07 mEq/l, (P less than 0.02), as sodium intake increased, partly due to increased urinary potassium excretion (mean cumulative potassium loss of 129 mEq). Thus, changes in potassium balance may be important in modulating the sodium-associated variation in aldosterone secretion.

Effect of alpha-human atrial natriuretic peptide in low renin essential hypertension and primary aldosteronism

Atrial natriuretic peptide (ANP), besides its diuretic and antihypertensive effects, exhibits an "in vitro" inhibitory action on aldosterone. In order to elucidate if these effects are present also "in vivo", we injected 100 micrograms of alpha-human ANP as a bolus in normal volunteers, low renin essential hypertensive subjects (LRH) and in patients with primary aldosteronism (PA). A transient hypotensive effect was seen in all patients, without significant variations of heart rate. The diuretic and saluretic effects of ANP were greater in hypertensive subjects, even in PA where endogenous ANP levels are known to be elevated. Plasma aldosterone values decreased significantly only in normal volunteers. In conclusion, in LRH and PA renal effects of ANP are not diminished, although its aldosterone-inhibiting properties are less evident than in normals.

Contribution of elevated peripheral resistance to acute volume loaded hypertension in dogs

The role of peripheral resistance in volume loaded hypertension was examined by measuring changes in hemodynamic and humoral factors during dextran infusion for one hour, and for three hours after stopping the infusion in 30 anesthetized dogs. The mean blood pressure was elevated significantly (118%, p less than 0.01), accompanied by increased cardiac output (170%, p less than 0.01) during volume loading. In the recovery period, cardiac output returned to the basal level while the total peripheral resistance gradually increased (118%, p less than 0.01) contributing to the maintenance of high blood pressure (108%, p less than 0.01). There was no significant correlation between the hematocrit change and the increase in peripheral resistance in the recovery period. The levels of plasma norepinephrine, epinephrine, renin activity and vasopressin were suppressed by volume loading. These results demonstrated the importance of increase in peripheral resistance for maintaining high blood pressure in this acute volume excess model. The participation of the renin-angiotensin system, the sympathetic nervous system and vasopressin were all excluded and vascular structural changes were most unlikely to be involved in this acute experiment. It remains unknown whether this conversion is attributable to the summation of local autoregulation or to some other factors.

Specific binding and steroidogenetic effects of atrial natriuretic factor (ANF) in Leydig cells of rats

Atrial natriuretic factors (ANF) may influence testicular steroidogenesis. This study was conducted to evaluate the presence of specific ANF-binding on isolated adult rat Leydig cells and the effects of ANF on testosterone production. Indirect immunofluorescence technique demonstrates that adult rat Leydig cells possess specific ANF-binding and that rAP-II strongly stimulates the testosterone production. rAP-II exerts its maximal stimulatory effect on the testosterone secretion at low doses (10(-11) M), corresponding at the physiological plasmatic concentration in the adult normal rat. High doses (10(-9)-10(-7) M) of rAP-II show a decline in the stimulatory effect on testosterone secretion. Our data suggest that rAP-II influences the testicular steroidogenesis by a receptorial mechanism; the biphasic effect of rAP-II on the testosterone production may be related to an acute receptorial desensitization phenomena.

Captopril attenuates diuretic and natriuretic actions of furosemide but not atrial natriuretic peptide

Atrial Natriuretic Peptide (ANP) exerts a potent diuretic and natriuretic action in rat, dog and man. To test whether these actions of ANP are due to antagonism of the antinatriuretic actions of endogenous angiotensin II, an examination was made of the renal actions of ANP in anesthetized rats with and without captopril pretreatment. Captopril treatment did not alter the diuretic and natriuretic action of a single, intravenous bolus injection of ANP (1000 ng of the 8-33 ANP). Captopril treatment did significantly attenuate the diuretic and natriuretic actions of Furosemide (20 mg/kg ip). This attenuation was not reversed by concomitant, exogenous angiotensin II infusion. These results suggest that while ANP exerts its renal actions independently of the circulating renin-angiotensin system the diuretic and natriuretic action of Furosemide is modulated by a substrate of angiotensin converting enzyme.

Inhibitors of aldosterone secretion

Aldosterone secretion may be inhibited by potassium depletion, inhibitors of the renin-angiotensin system, dopamine and atrial natriuretic factor. The latter appears to be an important physiological regulator of aldosterone secretion. ANF inhibits basal, ACTH, Angiotensin II and potassium-stimulated aldosterone production in vitro by a direct action on the adrenal gland. In vivo data also support a direct inhibitions of aldosterone. The stimulation of aldosterone secretion by infusions of Angiotensin II and potassium is inhibited by simultaneous infusions of ANF. Infusions of ANF lower the basal aldosterone secretion in man. The mechanism by which ANF inhibits aldosterone is not known. No unifying first step has been identified to explain ANF's ability to inhibit all stimuli. In vivo, part of the lowering of aldosterone levels may be due to inhibition of renin secretion. This effect of ANF upon renin is inconsistent and appears to depend upon the experimental conditions.

Estrogen effects on angiotensin receptors are modulated by pituitary in female rats

The present studies were designed to test the hypothesis that changes in angiotensin II (ANG II) receptors might modulate the altered target tissue responsiveness accompanying estradiol administration. Estradiol was infused continuously in oophorectomized female rats by employing minipumps to achieve plasma estradiol levels and simulating pregnancy levels in the rat. Aldosterone was also infused in control and experimental animals to avoid estrogen-induced changes in renin and ANG II. ANG II binding constants were determined in radioreceptor assays. Estradiol increased binding site concentration in adrenal glomerulosa by 76% and decreased binding sites of uterine myometrium and glomeruli by 45 and 24%, respectively. There was an accompanying increase in the affinity of ANG II binding to adrenal glomerulosa and uterine myometrium. Because estrogen is a potent stimulus of prolactin release from the pituitary of rodents, studies were also designed to test the hypothesis that prolactin may mediate some or all of the estrogen-induced effects observed. Hypophysectomy abolished estradiol stimulation of prolactin release and most ANG II receptor changes. The only effect that persisted was a 41% decrease in the density of uterine receptors. Prolactin administration to pituitary intact rats was associated with a 50% increase in receptor density of adrenal glomerulosa simulating estradiol administration. However, the changes in glomeruli and uterine myometrium were opposite in that both tissues also increased receptor density, suggesting that prolactin was not the sole mediator of the estrogen-induced receptor changes. In conclusion, regulation of ANG II receptors in a number of diverse target tissues by estradiol is complex with contributions from estrogens and pituitary factors, which include but do not exclusively involve prolactin.

Cardiovascular, renal, and endocrine response to atrial natriuretic peptide in angiotensin II mediated hypertension

Studies done in vitro have demonstrated that atrial natriuretic peptide (ANP) antagonizes angiotensin II-mediated contraction of vascular smooth muscle. The present studies were designed to examine the in vivo actions of ANP in acute angiotensin II-mediated hypertension. The cardiovascular, renal, and hormonal effects of intravenous ANP were evaluated in anesthetized normotensive (n = 6) and hypertensive (n = 6) dogs. In both groups, ANP (3.0 micrograms/kg bolus, 0.3 micrograms/kg/min continuous infusion) reduced arterial pressure and cardiac output without changing systemic vascular resistance. ANP specifically reduced renal vascular resistance and increased sodium excretion. The natriuresis observed was greater in hypertensive than in normotensive dogs. This occurred without a significant change in glomerular filtration rate or aldosterone. The ANP-mediated reduction in arterial pressure was associated with an increase in circulating arginine vasopressin and catecholamines but not in renin. These studies demonstrate that ANP-mediated hypotension results from a reduction in cardiac output without changing systemic vascular resistance, ANP acts as a specific renal vasodilator, ANP-mediated natriuresis can occur without alteration in glomerular filtration rate or aldosterone, and ANP specifically inhibits the release of renin without inhibiting the release of other circulating vasoconstrictors.

Atrial natriuretic peptide inhibits protein phosphorylation stimulated by angiotensin II in bovine adrenal glomerulosa cells

Bovine adrenal glomerulosa cells were incubated with 32PO4 and either angiotensin II, atrial natriuretic peptide, or both. Solubilized cells were subjected to one-dimensional gel electrophoresis. Autoradiography and scintillation counting of gels showed that angiotensin increased labeling of one band, with an apparent molecular weight of 17,600. Atrial natriuretic peptide inhibited the angiotensin effect. Together with earlier results, this observation suggests that atrial natriuretic peptide affects aldosteronogenesis at the level of protein phosphorylation, but not by altering angiotensin receptors, calcium fluxes or phosphoinositide metabolism.

Plasma levels of immunoreactive atrial natriuretic factor increase during supraventricular tachycardia

A significant diuretic and natriuretic response occurs during paroxysmal supraventricular tachycardia (SVT). Although the diuresis may be secondary to suppression of vasopressin secretion, the etiology of the natriuresis remains unexplained. To determine if atrial natriuretic factor (ANF) could contribute to the polyuric response during SVT, 10 patients were studied: five during spontaneous SVT and five during simulated SVT produced by rapid simultaneous atrial and ventricular pacing. Plasma immunoreactive ANF (IR-ANF) levels measured by radioimmunoassay were obtained at baseline (before and/or 24 to 48 hours after SVT) and after at least 15 minutes of SVT in all patients. During spontaneous and simulated SVT, IR-ANF was significantly elevated (mean +/- SE; 275 +/- 68 pmol/L) compared to baseline (28 +/- 7 pmol/L; p = 0.0036). Similar increases in IR-ANF were noted during both simulated and spontaneous SVT. To determine if this IR-ANF release was related to the increase in heart rate or the rise in right atrial pressure during SVT, IR-ANF levels were also measured in five patients with sinus tachycardia and in six patients with congestive heart failure. IR-ANF was significantly related to right atrial pressure (r = 0.93; p = 0.0009) but not to heart rate (r = 0.46). Thus, IR-ANF is elevated during SVT and may contribute to the natriuretic response. The stimulus to IR-ANF secretion during SVT appears to be related to the rise in right atrial pressure rather than to the increase in heart rate.

Atrial natriuretic factor in normal subjects and heart failure patients. Plasma levels and renal, hormonal, and hemodynamic responses to peptide infusion

We investigated atrial natriuretic factor (ANF) in humans, measuring plasma immunoreactive (ir) ANF (in femtomoles per milliliter), and renal, hormonal, and hemodynamic responses to ANF infusion, in normal subjects (NL) and congestive heart failure patients (CHF). Plasma irANF was 11 +/- 0.9 fmol/ml in NL and 71 +/- 9.9 in CHF (P less than 0.01); the latter with twofold right ventricular increment (P less than 0.05). In NL, ANF infusion of 0.10 microgram/kg per min (40 pmol/kg per min) induced increases (P less than 0.05) of absolute (from 160 +/- 23 to 725 +/- 198 mueq/min) and fractional (1-4%) sodium excretion, urine flow rate (from 10 +/- 1.6 to 20 +/- 2.6 ml/min), osmolar (from 3.2 +/- 0.6 to 6.8 +/- 1.2 ml/min) and free water (from 6.8 +/- 1.6 to 13.6 +/- 1.6 ml/min) clearances, and filtration fraction (from 20 +/- 1 to 26 +/- 2%). Plasma renin and aldosterone decreased 33% and 40%, respectively (P less than 0.01). Systolic blood pressure fell (from 112 +/- 3 to 104 +/- 5 mmHg, P less than 0.05) in seated NL; but in supine NL, the only hemodynamic response was decreased pulmonary wedge pressure (from 11 +/- 1 to 7 +/- 1 mmHg, P less than 0.05). In CHF, ANF induced changes in aldosterone and pulmonary wedge pressure, cardiac index, and systemic vascular resistance (all P less than 0.05); however, responses of renin and renal excretion were attenuated. ANF infusion increased hematocrit and serum protein concentration by 5-7% in NL (P less than 0.05) but not in CHF.

Prolonged administration of human atrial natriuretic peptide in healthy men. Reduced aldosteronotropic effect of angiotensin II

The effect of angiotensin II (5, 10, 20 ng/kg/min) on blood pressure and on the plasma concentrations of aldosterone was studied in six healthy men with and without the concomitant administration of synthetic human atrial natriuretic peptide given 1) as an i.v. bolus of 25 micrograms followed by a 6-hour infusion of 25 micrograms/hr or 2) as an i.v. bolus of 175 micrograms followed by a 6-hour infusion of 100 micrograms/hr. The pressor effect of angiotensin II (i.e., the rise of mean blood pressure above individual basal levels) remained unchanged during the administration of both doses of human atrial natriuretic peptide. The angiotensin II-induced rise in plasma concentrations of aldosterone in terms of absolute values) was reduced by human atrial natriuretic peptide during both trials. The rise in plasma concentrations of aldosterone above individual basal concentrations was also reduced during the administration of human atrial natriuretic peptide, although this effect was only marginal during the low dose experiment. These effects of human atrial natriuretic peptide support the contention that its therapeutic impact in hypertensive patients might be mediated in part by a reduction of high aldosterone concentrations.

Steroidogenic effect of atrial natriuretic factor in isolated mouse Leydig cells is mediated by cyclic GMP

The effects of different atrial natriuretic peptides on cyclic GMP formation and steroidogenesis have been studied in Percoll-purified mouse Leydig cells. Rat atrial peptides rANP (rat atrial natriuretic peptide), rAP-I (rat atriopeptin I) and rAP-II (rat atriopeptin II), in the presence of a phosphodiesterase inhibitor, stimulated cyclic GMP formation in a concentration-dependent manner. In the presence of saturating concentrations of the peptides, a 400-600 fold stimulation of cyclic GMP accumulation was observed. Among the peptides, rAP-II appeared to be the most potent. ED50 values (concentration causing half-maximal effect) for rAP-II, rANP and rAP-I were 1 X 10(-9) M, 2 X 10(-9) M and 2 X 10(-8) M respectively. A parallel stimulation of cyclic GMP formation and testosterone production by the cells was observed after incubation of the cells with various concentrations of rAP-II. In the presence of a saturating concentration of rAP-II (2 X 10(-8) M), maximum stimulation of intracellular cyclic GMP content was obtained within 5 min of incubation. Testosterone production by mouse Leydig cells could be stimulated by 8-bromo cyclic GMP in a concentration-related manner. At a 10 mM concentration of the cyclic nucleotide, steroidogenesis was stimulated to a similar extent as that obtained with a saturating concentration of human chorionic gonadotrophin (5 ng/ml). On the basis of these results we conclude that cyclic GMP acts as a second messenger in atrial-peptide-stimulated steroidogenesis in mouse Leydig cells. The steroidogenic effect of atrial peptides appears to be species-specific, since none of these peptides stimulated testosterone production by purified Leydig cells of rats, though in these cells a 40-60-fold stimulation of cyclic GMP formation in response to each of the three peptides was observed. However, 8-bromo cyclic GMP could stimulate testosterone production in rat Leydig cells. Therefore we conclude that the lack of steroidogenic response in rat Leydig cells to atrial-natriuretic-factor-stimulation results from an insufficient formation of cyclic GMP in these cells. This species difference would appear to result from a lower guanylate cyclase activity in rat Leydig cells.

Specific receptors for atriopeptin III in rabbit lung

Binding studies revealed the presence of a single class of high affinity binding sites for atriopeptin III on rabbit lung membranes. An apparent dissociation constant (Kd) of 0.32 nM and a binding capacity of 166 fmol/mg protein was determined. Binding was time-dependent and saturable. The relative binding affinities of atrial peptide analogs correlated well with their potencies in eliciting relaxation of norepinephrine-contracted rabbit aorta strips. Unrelated peptide hormones did not compete for the atriopeptin binding site on rabbit lung membranes. The atrial peptide binding data are similar to those obtained for other tissues and indicate the presence of a physiologically relevant atrial peptide receptor in lung.

Effect of intracerebroventricular atrial natriuretic polypeptide on blood pressure and urine production in rats

In order to clarify the role of atrial natriuretic polypeptide (ANP) in the brain on regulation of blood pressure and urine output, we examined the effects of intracerebroventricular (i.c.v.) administration of synthetic alpha-human ANP (alpha-hANP) to both anesthetized and conscious rats. In anesthetized rats, i.c.v. injection of angiotension II (A II) caused increases of blood pressure, urine flow and sodium excretion in a dose dependent manner. alpha-HANP alone had no effect on these two parameters. The hypertensive effect of A II was apparently attenuated by concurrent injection of alpha-hANP, while, the diuretic response to A II was not changed by alpha-hANP. In conscious spontaneously hypertensive rats, i.c.v. injection of saralasin (an A II antagonist) produced a decrease in blood pressure. The i.c.v. pretreatment with alpha-hANP significantly potentiated the central depressor effect of saralasin. These findings suggest that brain ANP may be involved in controlling blood pressure in the central renin-angiotensin system.

Differential effects of transforming growth factor type beta on the growth and function of adrenocortical cells in vitro

Transforming growth factor type beta (TGF-beta) suppresses basal as well as corticotropin (ACTH)-stimulated steroid formation by bovine adrenocortical cells in culture. The effect is dose dependent and is not accompanied by any change in adrenocortical cell growth. The minimum effective dose of TGF-beta is 4 X 10(-13) M (10 pg/ml), and maximal inhibition is observed at a concentration of 4 X 10(-11) M (1 ng/ml). A 16- to 20-hr incubation with TGF-beta is required to decrease steroidogenesis, and 12-18 hr are required before cells treated with TGF-beta recover complete responsiveness to corticotropin. Increases in cAMP mediated by corticotropin, forskolin, and isobutylmethylxanthine are not modified by the addition of TGF-beta; thus adenylate cyclase activity is unaffected by TGF-beta. Although TGF-beta inhibits the formation of all of the delta 4-steroids measured (including cortisol, corticosterone, aldosterone, and androstenedione), its effect can be completely reversed by the addition of 25-hydroxycholesterol, pregnenolone, or progesterone to the cells. In contrast, the addition of low density lipoprotein has no effect suggesting that TGF-beta targets the conversion of cholesterol precursors to cholesterol. The results demonstrate a highly potent effect of TGF-beta on the differentiated function of the adrenocortical cell. The inhibition of steroidogenesis can be dissociated from any effect on cell proliferation, and it occurs distal to the formation of cAMP but proximal to the formation of cholesterol. The results suggest that in the adrenal, TGF-beta or TGF-beta-like proteins may be playing an important role in modifying the differentiated state of the adrenocortical cell.

The atrial natriuretic factor

In less than three years since the rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats was reported the factor responsible for the diuretic, natriuretic, and vasodilating activity of the atrial homogenates was isolated, its chemical structure elucidated, and its total synthesis achieved. Also the cDNA and the gene encoding for the atrial natriuretic factor in mice, rats, and man have been cloned and the chromosomal site identified. The major effects of this hormone are vasodilatation, prevention and inhibition of the contraction induced by noradrenaline and angiotensin II, diuresis, and natriuresis associated in most instances with a pronounced increase in glomerular filtration rate and filtration fraction, inhibition of aldosterone secretion, and considerable stimulation of particulate guanylate cyclase activity. High density specific binding sites have been demonstrated in the zona glomerulosa of the adrenal cortex, in the renal glomeruli, and in the collecting ducts, and in the brain areas involved in the regulation of blood pressure and of sodium and water (AV3V region, subfornical organ, nucleus tractus solitarius, area postrema).

Atrial natriuretic peptide mRNA is regulated by glucocorticoids in vivo

In these studies glucocorticoids were found to increase the plasma levels of atrial natriuretic peptide (ANP) as well as the expression of the ANP gene in the Sprague-Dawley rat. Plasma ANP rose two-fold after 48 hrs. of exposure to dexamethasone (1 mg/day) in both intact and adrenalectomized animals. This was accompanied by a 1.5-2.0 fold increase in the levels of atrial and ventricular ANP transcripts. Deoxycorticosterone acetate (5 mg/day), administered on the same schedule, failed to increase either plasma ANP levels or cardiac ANP mRNA accumulation. These effects suggest that ANP may have a potential role as a mediator of glucocorticoid activity in the cardiovascular system and support the hypothesis that ANP is a glucocorticoid-regulated gene.

Plasma and atrial content of atrial natriuretic factor in cardiomyopathic hamsters

Immunoreactive atrial natriuretic factor (IR-ANF) was measured in plasma and atrial extracts from normal and cardiomyopathic Syrian golden hamsters. Plasma IR-ANF was increased from 84.8 +/- 9.8 pg/ml (n = 17) to 234 +/- 23 (n = 25; P less than .0001) in hamsters with moderate failure, and to 1085 +/- 321 pg/ml (n = 10; P less than .02) in animals with severe failure. Plasma IR-ANF increased with increased atrial hypertrophy. Atrial IR-ANF content was essentially the same in normal animals and in those with moderate heart failure (3.06 +/- 0.28 vs. 3.17 +/- 0.19 microgram/100 g body wt.) and lower in the majority of those with severe failure (1.82 micrograms/100 g body wt., P less than .001). The elevations of IR-ANF in plasma are similar to those seen in patients with congestive heart failure. Our studies do not support bioassay results showing a deficiency of atrial ANF content as being important in the congestive heart failure associated with cardiomyopathy in the hamster.

Binding sites of atrial natriuretic peptide in tree shrew adrenal gland

Adrenal gland binding sites for atrial natriuretic peptide-(99-126) (ANP) were quantitated in tree shrew (Tupaia belangeri) by incubation of adrenal sections with (3-[125I]-iodotyrosyl28) atrial natriuretic peptide-(99-126), followed by autoradiography with computerized microdensitometry. In the adrenal glands, there are three types of ANP binding sites. One is located in the zona glomerulosa (BMax 84 +/- 6 fmol/mg protein; Kd 122 +/- 9 pM); the second in the zona fasciculata and reticularis (BMax 29 +/- 2 fmol/mg protein; Kd 153 +/- 6 pM) and the third in the adrenal medulla (BMax 179 +/- 1 fmol/mg protein; Kd 70 +/- 2 pM). Besides the influence of ANP on the regulation of adrenocortical mineralcorticoid and glucocorticoid secretion our findings raise the possibility for a local site of action of atrial natriuretic peptide in the regulation of adrenomedullary catecholamines in the tree shrew, primates and man.

Atrial natriuretic peptide in chronic heart failure in the rat: a correlation with ventricular dysfunction

To assess the relation between atrial natriuretic peptide and ventricular dysfunction, we simultaneously measured both atrial and plasma immunoreactive atrial natriuretic peptide concentrations in rats 4 weeks after myocardial infarction induced by left coronary artery ligation. When compared to controls (n = 39), rats with infarction (n = 16) had markedly elevated plasma immunoreactive atrial natriuretic peptide concentrations (1205.8 +/- 180.9 vs. 126.7 +/- 8.9 pg/ml, p less than 0.001) and reduced immunoreactive atrial natriuretic peptide concentrations in right and left atria (31.4 +/- 4.6 vs. 61.2 +/- 3.2 ng/mg, p less than 0.001; 14.9 +/- 2.2 vs. 32.7 +/- 2.4 ng/mg, p less than 0.001, respectively). Right ventricular weight increased in proportion to infarct size, and both were correlated with plasma immunoreactive atrial natriuretic peptide levels (r = 0.825, p less than 0.001 and r = 0.816, p less than 0.001, respectively). Right atrial immunoreactive atrial natriuretic peptide content was significantly higher than left in both controls and rats with infarction. Both right and left atrial immunoreactive atrial natriuretic peptide concentrations were negatively correlated with both right ventricular weight as well as plasma immunoreactive atrial natriuretic peptide concentrations (right atrium: r = -0.816, p less than 0.001, r = -0.708, p less than 0.01; left atrium: r = -0.687, p less than 0.01, r = -0.644, p less than 0.01, respectively). These results suggest that chronic stimulation of atrial natriuretic peptide release from both atria is associated with increased turnover and depleted stores of atrial natriuretic peptide in atria in proportion to the severity of heart failure. It also suggests that plasma atrial natriuretic peptide levels may be used as a reliable index of cardiac decompensation in chronic heart failure.

Atrial natriuretic peptide and atrial pressure in patients with congestive heart failure

To define the relation between atrial pressures and the release of atrial natriuretic peptide, we measured plasma concentrations of the peptide in 26 patients with cardiac disease--11 with normal atrial pressures and 15 with elevated atrial pressures (11 of these 15 had elevated pressures in both atria). Mean peptide levels (+/- SEM) in the peripheral venous blood were increased in the 11 patients with cardiac disease and normal atrial pressures, as compared with 60 healthy controls (48 +/- 14 vs. 17 +/- 2 pmol per liter). In the patients with elevated atrial pressures, peptide concentrations were increased twofold in peripheral venous, right atrial, pulmonary arterial, and systemic arterial plasma, as compared with the concentrations in the patients with normal atrial pressures. A step-up in peptide concentration was seen between the venous and right atrial plasma (P less than 0.002) and between the pulmonary and systemic arterial plasma (P less than 0.01), suggesting release of the peptide from the atria. A linear relation was found between right atrial pressure and right atrial peptide concentration (r = 0.835, P less than 0.001) and between pulmonary wedge pressure and the systemic arterial peptide concentration (r = 0.866, P less than 0.001). Right atrial pressure and the peptide concentration both increased with exercise testing in the nine patients evaluated. We conclude that the release of atrial natriuretic peptide is at least partly regulated by right and left atrial pressures. Distinguishing the relative contributions of the two atria and defining the role of peptide release in the pathogenesis of heart failure will require further investigation.