Inhibition of aldosterone production by an atrial extract

Atrial natriuretic factor is unlikely to be involved in the reduced aldosterone production in the Brattleboro rat

We have previously reported that basal and stimulated aldosterone production in Brattleboro rat (DI) lacking hypothalamic arginine vasopressin is lower than that observed in control Long-Evans rat (LE). In the present study, we investigated the secretion under various experimental conditions, adrenal binding sites, and the aldosterone-inhibiting effect of atrial natriuretic factor (ANF). In the conscious resting state, the plasma ANF concentration was similar between LE and DI rats. Pentobarbital anaesthesia (5 mg/100 g body wt.) reduced the plasma ANF concentration equally in both groups, with or without captopril pretreatment. Morphine (10 mg/100 g body wt.) increased ANF secretion dramatically and equally in the two groups of pentobarbital anaesthetized (2 mg/100 g body wt.) rats. In dexamethasone pretreated-pentobarbital anaesthetized rats, a concurrent i.v. ANF infusion (50 ng/min) did not change significantly the corticosterone response to ACTH (1-24) (1 mI.U./100 g body wt.) but steeply depressed ACTH-induced aldosterone production to a similar extent between DI and LE rats. A single class of adrenal ANF receptor sites was found with a similarity in high affinity and maximum binding capacity between the two groups of rats. Taken together, these results suggest that the reduced aldosterone production by Brattleboro rat adrenals is unlikely to be related to the inhibitory effect of ANF.

The effect of splanchnic nerve stimulation on the uptake of atrial natriuretic peptide by the adrenal gland in conscious calves

A technique has been developed with which it has been possible to quantify the output of a wide variety of agonists including catecholamines, glucocorticoids, mineralocorticoids, enkephalins and various peptides, from the adrenal gland in the conscious unrestrained calf; also to investigate responses to electrical stimulation of the peripheral end of the splanchnic nerve below any behavioural threshold. In the present study this methodology has been employed to investigate the extent to which stimulation of the splanchnic sympathetic innervation affects adrenal handling of atrial natriuretic peptide as this peptide has been identified within the adrenal medulla in this species. Stimulation of the splanchnic nerve at frequencies which raised the concentration of atrial natriuretic peptide like-immunoreactivity (ANP) by 25% led to an abrupt increase in the uptake of the peptide by the right adrenal gland by about 250%. During nerve stimulation more than 20% of the ANP that was estimated to be presented to the gland was taken up, by comparison with less than 13% of the amount presented which was taken up before and after stimulation. These results suggest that stimulation of the splanchnic nerve may specifically enhance the uptake of ANP by the adrenal gland and represent the first report of such a mechanism in respect of any biologically active peptide so far as we are aware.

Effect of pro-atrial natriuretic peptides 1-30, 31-67 and 99-126 on angiotensin II-stimulated aldosterone production in calf adrenal cells

Pro-atrial natriuretic peptide (Pro-ANP) is a 126 amino acid peptide from which atrial natriuretic peptide (ANP) (99-126 amino acid) is derived. ANP has potent diuretic, natriuretic and vasodilatory peptides. ANP is also a potent direct and indirect inhibitor of aldosterone secretion. The N-terminus of the ANP prohormone containing the peptides 1-30 and 31-67 have been demonstrated to have diuretic, natriuretic and vasodilatory properties. Dispersed calf zona glomerulosa cells were incubated with angiotensin II (A-II) and increasing concentrations of the ANP, ProANP 1-30 and 31-67 to determine if their reported natriuretic activity was mediated through suppression of aldosterone secretion. ANP as reported by many investigators produced a dose-dependent and potent inhibition of A-II-mediated aldosterone secretion. The Pro-ANP 1-30 and 31-67 did not affect A-II-stimulated aldosterone secretion at any of the doses tested. This study shows that the reported natriuretic effect of the fragments is not mediated by inhibition of aldosterone secretion.

Angiotensin II-induced atrial natriuretic factor release in dogs is not related to hemodynamic responses

Angiotensin II (Ang II) and atrial natriuretic factor (ANF) appear to act as functional antagonists in the regulation of fluid and electrolyte homeostasis and blood pressure. To further define the relations between these hormones in vivo, we investigated the effect of low doses of Ang II (1-10 ng/kg/min) on plasma ANF levels. We also evaluated the influence of ANF release on the renal and hormonal responses to ANG II. Studies were performed in anesthetized and conscious instrumented dogs during sustained saline load and converting enzyme inhibition. In the anesthetized dogs, Ang II significantly increased plasma ANF levels and ANF arteriovenous difference without changing either atrial pressures or hematocrit. In both conscious and anesthetized dogs, ANF increases were not correlated with blood pressure responses to Ang II and did not occur in control groups when Ang II was replaced by vehicle. Ang II-induced sodium retention and stimulation of aldosterone production were attenuated, and renin suppression was enhanced in dogs having the largest changes in plasma ANF in response to converting enzyme inhibition or Ang II. These results demonstrate that in volume-replete dogs Ang II can promote ANF release independently of changes in atrial pressures or systemic hemodynamics, suggesting that Ang II may exert a significant modulatory effect on ANF secretion. The results also show significant relations between ANF and renal and adrenal responses to Ang II, which may suggest that, in turn, endogenous ANF modulates the effects of Ang II.

Atrial natriuretic peptide response to ionic and nonionic contrast left ventriculography

Atrial natriuretic peptide (ANP) levels were measured prior to and at 1 and 5 minutes postcontrast left ventriculography with an ionic contrast agent (diatrizoate), and a nonionic agent (iopamidol) and the results were compared. Since ionic contrast agents have been found to cause an increase in left ventricular end-diastolic pressure (LVEDP) and nonionic agents have been found to have less of an effect on LVEDP, we investigated the response of ANP levels, which have been found to increase secondary to increased LVEDP (atrial pressure), with both agents. A group of 38 patients who were scheduled for left heart catheterization for suspected coronary artery disease was included (19 in each group) and blood samples for ANP levels were drawn from the left ventricles. At the same time, heart rate, LVEDP, and left ventricular systolic pressure (LVSP) were also measured. It was found that the LVEDP increased significantly for both agents at 1 minute postventriculography, but no further change occurred at 5 min. Heart rate increased significantly in the diatrizoate group at 1 minute with a return of heart rate to preventriculography levels at 5 min, while the ANP level and LVSP remained unchanged at 1 minute postventriculography with both agents but increased significantly at 5 min in the diatrizoate group only. This difference in ANP response is not correlated with the LVEDP. The response of ANP may be related to heart rate and/or LVSP.

Regulation of atrial natriuretic peptide receptors in glomeruli during chronic salt loading

The effects of chronic salt loading on atrial natriuretic peptide (ANP) receptor density and affinity were studied in isolated renal glomeruli of male Sprague-Dawley rats, which received 0.9% saline as drinking fluid (NaCl-rats) and a normal rat chow diet for 35 days (N = 12). Animals on a low sodium intake received the same diet, but deionized water and served as controls (C) (N = 12). After 35 days blood pressure was only slightly increased to 136 +/- 9 in NaCl-rats versus 120 +/- 2 mm Hg in C (NS). Glomerular filtration rate, plasma cGMP and plasma ANP remained unaltered. Determination of total ANP receptor characteristics in these rats indicated a significant down-regulation of ANP receptors in salt loaded rats. Since ANP-stimulated cGMP formation was not affected by salt loading, the roles of clearance (C) and of biologically active (B) receptors were further evaluated at 21 degrees C on freshly isolated and acid washed (pH 5) glomeruli in seven animals after 35 days of salt loading and in seven animals on a low sodium intake. B-receptors were assessed by blocking C-receptors with 4-23 cANP. C-receptor numbers were lower in NaCl-rats (97 +/- 8 vs. 184 +/- 14 fmol/mg protein in C; N = 7; P less than 0.02), while C-receptor affinity was increased (Kd: 12 +/- 3 pM in NaCl-rats vs. 22 +/- 5 pM in C; P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Atriopeptin prevents angiotensin II-stimulated glucose utilization in the subfornical organ

Previous studies have shown that angiotensin II (ANG II) increases glucose utilization in the subfornical organ and stimulates drinking behavior. We investigated with the deoxyglucose method whether atriopeptin III, an atrial natriuretic peptide (ANP), would prevent this enhanced glucose metabolism and interfere with the drinking response in the presence of ANG II. Two rat models with high circulating levels of ANG II were studied: the homozygous Brattleboro and ANG II-infused Sprague-Dawley rats. ANP decreased the normally enhanced glucose utilization in the subfornical organ in the Brattleboro rat and inhibited ANG II-stimulated glucose metabolism in the subfornical organ of Sprague-Dawley rats. This effect was accompanied by decreased ANG II-stimulated water intake. These findings indicate that ANP may act at the level of subfornical organ to antagonize the dipsogenic action of ANG II.

Atrial natriuretic polypeptide after burn injury: blood levels and physiological role in rats

To define the relationship between atrial natriuretic polypeptide and the physiological changes of water and electrolytes after burns, the changes in plasma hormonal levels, including atrial natriuretic polypeptide, and urinary water and sodium excretions were examined in burned rats. Further, to elucidate the physiological significance of atrial natriuretic polypeptide after burns, the effects of a specific antiserum against atrial natriuretic polypeptide were determined in burned rats. Plasma atrial natriuretic polypeptide levels in rats following 30 per cent BSA full skin thickness burns were elevated for sustained periods (432.3 +/- 156.5 pg/ml, P less than 0.01 on day 1 postburn, 244.5 +/- 73.7 pg/ml, P less than 0.05 on day 3 postburn). Urine volume and sodium excretion decreased significantly during the first 72 h after burns. On day 3 postburn, urine volume and sodium excretion began to increase significantly. Specific rabbit antiserum against atrial natriuretic polypeptide was injected into the burned rats during this diuretic phase. Significant inhibition of diuresis and natriuresis was observed after the injection of antiserum (27.5 +/- 2.4 per cen decrease in urine volume, 57.1 +/- 10.4 per cent decrease in sodium excretion). These results suggest that atrial natriuretic polypeptide plays a physiological role in the regulation of urinary water and sodium excretion after burns.

Role of endogenous ANP on endocrine function investigated with a monoclonal antibody

Substantial volume expansion in conscious rats induces a strong natriuresis, cyclic GMP excretion, increase in cyclic GMP in plasma and kidney tissue, decrease in plasma renin activity and plasma aldosterone concentration. These effects are directly related to an increase in plasma levels of atrial natriuretic peptides. The renal response and the changes in plasma and kidney cyclic GMP, plasma renin activity and aldosterone could be totally blocked by simultaneous administration of monoclonal antibodies directed against ANP. From this study it seems to be clear that the rise in cyclic GMP and the inhibition of the renin-aldosterone system is not a direct effect of volume expansion but is specifically mediated by the released ANP. The great importance of ANP in acute volume expansion made us wonder about the role of ANP in chronic volume expansion and under basal conditions without volume loading. Chronic volume loading was induced pharmacologically by the sodium retaining vasodilatator minoxidil. Under both chronic volume expansion and basal conditions the neutralization of the circulation ANP by antibody administration leads to reduced plasma cyclic GMP levels. No alterations in urinary sodium excretion, plasma renin activity and plasma aldosterone concentration could be observed: In conclusion, the monoclonal antibody directed against ANP is a useful tool for the investigation of the physiological role of endogenous ANP.

Localization of atrial natriuretic peptide/cardiodilatin (ANP/CDD)-immunoreactivity in the lacrimal gland of the domestic pig

The presence of atrial natriuretic peptic/cardiodilatin-immunoreactive material was demonstrated in the lacrimal gland of the domestic pig by high performance liquid chromatography and radioimmunoassay. The immunohistochemical localization revealed a distinct population of cuboid or spindle-shaped ANP/CDD-IR cells in the epithelium of the terminal portion of the secretory tubules. In addition, a moderate number of positive cells was localized intraepithelially in the intralobular ducts as well as the connective tissue between these ducts. Our findings provide a morphological indication that ANP/CDD may play a physiological role in the regulation of sodium transport and secretion in the lacrimal gland.

Presence of immunoreactive atrial natriuretic peptides in pericardial fluid of human subjects with congenital heart diseases

The epicardial release of immunoreactive atrial natriuretic peptides (ir-ANPs) in inside-out perfused rabbit atria has been reported. In order to determine the presence of ir-ANPs in pericardial fluid and to evaluate their biochemical characteristics, we measured the concentration of ir-ANPs in pericardial fluid obtained from the patients with congenital heart diseases during open heart surgery. Serial dilution curves made with the extrats of pericardial fluid using Sep-Pak C18 cartridges were parallel with standard curve. The concentration of ir-ANPs in pericardial fluid was significantly lower than the corresponding plasma concentration. On gel permeation and reverse-phase high performance liquid chromatography, the ir-ANPs in pericardial fluid, plasma and atrial appendage showed both high and low molecular weights. The major peak of ir-ANPs in plasma was observed at the corresponding fraction to the alpha-human ANP and considerable amount of high molecular weight form of ir-ANPs was observed in pericardial fluid. However, the major peak of ir-ANPs in atrial appendage was observed at the corresponding fraction to the rat pro-ANP. The data suggest that ir-ANPs exist both high and low molecular weight forms in pericardial fluid.

Evidence that atriopeptin is not a physiological regulator of sodium excretion

Although much experimental evidence is consistent with the concept that atrial natriuretic factor (atriopeptin) is an important physiological regulator of renal sodium excretion, this hypothesis remains unproven. Indeed, a rapidly expanding collection of experimental data appears to be more compatible with the opposite conclusion, namely that circulating atriopeptin exerts only a trivial effect on renal sodium excretion during normal day-to-day living conditions. In this review, the substantial evidence demonstrating that elevations of plasma atriopeptin from threefold to 13-fold produce only a slowly developing and relatively modest natriuresis is reassessed in light of recently published data indicating that the acute intake of food (the pathway by which essentially all sodium enters the body under normal living conditions) does not increase circulating atriopeptin. These considerations imply that atriopeptin does not contribute to the process that elicits a postprandial natriuresis, a process that presumably is of primary importance in the physiological regulation of sodium balance. In addition, consideration is given to a number of common physiological, experimental, and pathophysiological conditions in which circulating atriopeptin does not correlate with renal sodium excretion. This lack of correlation implies that atriopeptin is not an important regulator of sodium excretion in these situations.

Impaired aldosterone production by long-term infusion of atrial natriuretic factor

This study assessed the effect of chronic infusions of atrial natriuretic factor (ANF) on in vivo and in vitro production of aldosterone. Vehicle (saline) or rat ANF-(99-126) was intravenously infused at 100 ng.kg-1.h-1 for 5 consecutive days into male New Zealand White rabbits. At 5 days plasma ANF was 18 +/- 4.1 pg/ml in vehicle-infused and 48.5 +/- 9.0 in ANF-infused rabbits (P less than 0.01). Plasma renin activity was significantly less in ANF-infused rabbits (2.99 +/- 0.35 vs. 0.77 +/- 0.12 ng.ml-1.h-1, P less than 0.01); however no differences were observed in the basal plasma concentrations of aldosterone, corticosterone, potassium, or hematocrit. In in vivo studies, chronically administered ANF attenuated plasma aldosterone, but not pressor, responses to acutely infused angiotensin II given at doses of 4, 16, and 64 ng.kg-1.min-1 for 20 min each. In in vitro experiments, collagenase-dispersed adrenal capsular cells from ANF-infused rabbits exhibited significantly reduced maximal responses to adrenocorticotropic hormone, angiotensin II, and potassium. These results suggest that chronic small increases in circulating ANF can blunt selectively adrenocortical responses to aldosterone secretagogues without affecting pressor responses to angiotensin II.

Phosphorylation of adrenal histone H3 is affected by angiotensin, ACTH, dibutyryl cAMP, and atrial natriuretic peptide

Angiotensin (AII) and atrial natriuretic peptide (ANP) exert opposite effects on phosphorylation of a 17.6 kDa nuclear protein from bovine adrenal glomerulosa cells. The protein was separated by sodium dodecyl sulfate electrophoresis and blotted onto polyvinylidene difluoride, and the N-terminal sequence was obtained. This sequence corresponded to histone H3. Another polyacrylamide gel electrophoresis system was used to confirm that AII stimulated the phosphorylation of histone H3. ACTH[1-24] stimulated phosphorylation of the same protein. Dibutyryl cAMP stimulated phosphorylation of a 17.6-kDa protein, and two gel electrophoresis systems confirmed that the protein affected was histone H3. In situ peptide mapping using papain, of either purified standard histone H3 or of the adrenal 17.6-kDa protein, produced the same major fragment as observed by silver staining. Therefore, the 17.6-kDa protein that is affected by AII, ANP, ACTH, and dibutyryl cAMP is histone H3. This finding suggests that in addition to their mutually antagonistic effects on acute steroidogenesis, AII and ANP may exert opposite effects on adrenal cell functions involving the nucleus.

Extracellular calcium regulates expression of the gene for atrial natriuretic factor

Primary cultures of neonatal rat cardiocytes were exposed for 24 hours to culture media containing 0-2.0 mM extracellular calcium. Both atrial natriuretic factor (ANF) messenger RNA (mRNA) and ANF secretion were increased approximately threefold in the presence of 2.0 mM CaCl2 (vs. Ca2(+)-free medium). When cardiocytes were treated with the calcium channel blockers diltiazem, nifedipine, or verapamil, both ANF synthesis and secretion fell to 25-40% of control values. The choice of transcription start site on the ANF gene was not altered by the calcium channel blockers. When exogenous calcium was added to cardiocytes treated with verapamil, secretion of ANF was partially restored to control levels. High-performance liquid chromatographic analysis of medium from cardiocytes exposed to varying extracellular calcium concentrations or treated with calcium channel blockers for 24 hours revealed that the majority of secreted immunoreactivity (60-70%) migrated with pro-ANF (17 kDa) and that none of the various experimental manipulations significantly changed the ratio of pro-ANF to ANF in the media. These results were confirmed by immunoprecipitation analysis of the culture medium from the individual treatment groups. Treatment of cardiocytes for 24 hours with either the calcium ionophore A23187 or the phorbol ester 12-O-tetradecanoylphorbol 13-acetate increased ANF secretion. The combined use of these agents resulted in stimulation of both ANF secretion and ANF mRNA accumulation.

Central and peripheral effects of the peptide ANF on renal function and blood pressure in hypertensive rats

1. The present study assesses renal and blood pressure effects of systemically and intracerebroventricularly (I.C.V.) administered atrial natriuretic factor (ANF) in anaesthetized New Zealand genetically hypertensive (NZGH) rats and their normotensive substrain (NZN). 2. Plasma ANF concentration was significantly raised in NZGH compared with NZN animals. Intravenous ANF administration increased circulating ANF concentration to similar levels in NZGH and NZN rats. Plasma aldosterone concentrations were initially similar in normotensive and hypertensive animals and were reduced markedly by I.V. ANF administration in both groups. 3. Peripheral administration of ANF produced a significant and sustained hypotension during the period of the hormone administration in NZGH animals, while arterial mean blood pressure (MBP) was not altered significantly in NZN rats. Central infusion of ANF produced no change in MBP in either NZGH or NZN animals. There was no detectable change in heart rate during central or peripheral administration of the hormone in either group. 4. By comparison with animals maintained on hormone-free infusate, urine flow changed little over the 80 min period of I.V. ANF infusion in NZGH rats but was markedly increased in NZN animals. Urinary sodium excretion was elevated during ANF infusion in both NZGH and NZN animals. Central infusion of ANF produced a diuresis in NZN rats but a slight reduction in urine flow in NZGH animals, while sodium excretion was not affected in either group. 5. It appears from the present study that central and peripheral ANF effects on renal function and blood pressure differ in hypertensive and normotensive animals. These differences may in part reflect adjustments to long-term elevation in plasma ANF in hypertension and in part are possibly associated with disturbances in related endocrine mechanisms.

Atrial natriuretic hormone and aldosterone regulation in salt-depleted state

To evaluate the effect of very low-dose infusion of atrial natriuretic hormone (ANH) on aldosterone regulation, seven normal young men were infused for 2.5 h with 0.47 pmol.kg-1.min-1 of human [Ser-Tyr28]ANH or placebo. During the last 0.5 h 4 pmol.kg-1.min-1 of angiotensin II were also infused. ANH plasma levels increased from 3.46 +/- 0.25 to a maximum of 6.80 +/- 0.88 pmol/l, which is well within normal limits. Plasma aldosterone decreased almost 40%, from 40.7 +/- 5.7 to 25.9 +/- 4.9 ng/dl after 2 h. ANH infusion caused a slight decrease in blood pressure and slight increase in renal excretion of sodium and potassium. These results suggest that even small changes in ANH levels, within the normal range, have physiological significance, particularly in aldosterone regulation.

Effect of atrial natriuretic factor on angiotensin converting enzyme

We studied the effects of atrial natriuretic factor on the conversion of angiotensin I to angiotensin II. Atrial natriuretic factor had a novel effect on angiotensin I conversion. Pulmonary artery endothelial cells converted 1.22 nmol/min/dish of [125I]angiotensin I to II in the absence of atrial natriuretic factor, but this activity was suppressed by atrial natriuretic factor. When atrial natriuretic factor was added to pulmonary artery endothelial cells, the conversion of angiotensin I to angiotensin II was suppressed 0.475 nmol/min/dish at 10(-6) M of atrial natriuretic factor.

Atrial natriuretic peptide, renin and aldosterone in obstructive lung disease and heart failure

Elevations of atrial natriuretic peptide (ANP) in congestive heart failure (CHF) and chronic obstructive lung disease (COLD) are presumably due to atrial hypertension, while secondary hyperaldosteronism in these patients is thought to result from diminished renal perfusion. The responsiveness of the ANP and renin (PRA)-aldosterone (PA) systems to acute increases in right atrial pressure has not been studied in these patients, but in normals a reciprocal relationship between ANP with PRA and PA has been shown. The authors monitored venous pressure (VP, reflective of right atrial pressure), ANP, PRA and PA in 15 stable COLD patients, seven stable CHF patients and three normal controls at baseline and after elevation of VP by antishock trousers. Inflation of the trousers resulted in increased VP and ANP (p less than 0.05): control ANP, 84 +/- 17 to 108 +/- 23 pg/ml; COLD ANP, 176 +/- 5 to 200 +/- 7; and CHF ANP, 388 +/- 20 to 499 +/- 37. PRA and PA were not suppressed by increasing ANP levels and the delta ANP/delta VP ratio was similar among groups. No intergroup differences in resting PRA and PA were noted, but PRA was higher (p = 0.007) and PA tended to be higher (p = 0.08) in a sub-group of six edematous patients, as compared with non-edematous patients and controls. These findings: (1) confirm previously reported ANP differences between COLD and CHF; (2) indicate that the ANP system remains responsive to physiologic manipulations in COLD and CHF; and (3) demonstrate that ANP and the PRA-PA axis are not reciprocally related in either group.

Stimulation of protein phosphorylation by atrial natriuretic factor in plasma membranes of bovine adrenal cortical cells

Atrial natriuretic factor (ANF) rapidly enhanced phosphorylation of plasma membrane proteins of bovine adrenal cortical cells. Pretreatment of the membranes with ANF (1 x 10(-8)M to 1 x 10(-7)M) resulted two- to four-fold in an incorporation of 32p-radioactivity from [gamma -32p]ATP as compared to the controls. The guanosine 3', 5' monophosphate (cGMP) which has been considered a second messenger of ANF also enhanced the phosphorylation of several proteins which were stimulated by ANF. However, the phosphorylation of certain proteins was stimulated differentially only by either ANF or cGMP. These results suggest that ANF-induced protein phosphorylation may play a role in transmembrane signalling pathway involving other second messenger(s) in addition to cGMP during the biological action of ANF.

Influence of endogenous opioids on atrial natriuretic factor release during exercise in man

To evaluate to what extent opioid secretion in exercise induces the release of atrial natriuretic factor (ANF), six healthy male volunteers who were trained subjects, were submitted to two maximal exercise tests with and without (control) opioid receptor blockade by Naltrexone. Blood samples were drawn before (rest) and after exercise (post-exercise) in order to measure human ANF (alpha h ANF), beta-endorphin, plasma aldosterone concentration (PAC) plasma renin activity (PRA) and adreno-cortico trophic hormone (ATCH) by radio-immunological methods. Expired gas was collected during exercise to measure oxygen consumption. On average, the same maximal oxygen consumption (VO2max) during exercise was reached by all subjects with and without treatment. Plasma ANF level at rest slightly decreased after administration of Naltrexone; the response to physical exercise was significantly reduced by Naltrexone. There was no statistical difference between plasma levels of beta-endorphin, PRA and ACTH at rest nor in the post-exercise situation under the influence of Naltrexone. The PAC increased significantly at rest after Naltrexone administration but there was no statistical difference between both values after exercise. These data demonstrate that: (1) ANF secretion during exercise is influenced by the level of beta-endorphin in the plasma; (2) the possible inhibitory role of ANF on aldosterone secretion during exercise is probably over-ruled by the increase in plasma ACTH and PRA.

Hemodynamic, hormonal, and renal effects of atrial natriuretic peptide in untreated congestive cardiac failure

We report the effects of intravenous infusion of the atrial natriuretic peptide analogue, met-ANP-26 (2 micrograms/min for 2 to 4 hours), in four patients with cardiomyopathy and severe congestive cardiac failure who had not received any previous cardiac therapy. The average cardiac index before infusion was 1.8 L/min/m2. Severe sodium and water retention was confirmed by high levels of total body water and extracellular liquid, whereas renal blood flow and glomerular filtration rate were reduced. Plasma concentration of ANP, norepinephrine, cortisol, and growth hormone were significantly increased before infusion. The infusion had no significant hemodynamic effect. After 2 hours urine volume had increased significantly from 51 to 76 ml/hr, urinary concentration of sodium from 72 to 90 mmol/L, and sodium excretion from 4.5 to 8.2 mmol/hr. The infusion was accompanied by a significant increase in plasma ir-ANP from 193 to 980 pg/ml. There were no significant effects on the plasma concentrations of norepinephrine, epinephrine, aldosterone, vasopressin, cortisol, growth hormone, or prolactin and no significant change in plasma renin activity. After 2 hours of infusion one patient had a severe sinus tachycardia and another had a sinus bradycardia. Both arrhythmias disappeared without harmful effects soon after the infusion was stopped.

An antiserum to atrial natriuretic factor (ANF) cross-reacts with neurophysins in the hypothalamo-neurohypophysial system of rat brain

The distribution of atrial natriuretic factor (ANF)-like reactivity was examined in rat brain and heart by immunohistochemistry. Immunostaining in heart was confined to atrial myocytes. In the hypothalamus, ANF-absorbable immunoreactivity was observed in magnocellular perikarya of the paraventricular and supraoptic nuclei, and in their projections to the neural lobe of the pituitary gland. No staining was seen in the preoptic or arcuate hypothalamic nuclei or in brain stem nuclei as previously reported by other investigators. The patterns of reactivity for ANF reported here is similar to that observed for neurophysins (NPs). Comparison of sequence data between rat ANF-28 and bovine NPs revealed three regions of 3 amino acid homology between these hypothalamic peptides. Preabsorption of the ANF antiserum with Affigel-coupled bovine NP I also resulted in complete elimination of all "ANF-immunoreactivity" in both atrium and hypothalamus. Cross-reactivity of the ANF antiserum with bovine NP I and II was further confirmed by Western blot analysis. Our findings suggest that ANF antisera can cross-react with NPs if they are directed against the shared antigenic epitopes; complete elimination of staining by preabsorption of the antibody with the immunogen, therefore, does not guarantee authenticity of localization. These observations may have relevance to an earlier study which reported on the existence of ANF-immunoreactivity in oxytocin neurons of the hypothalamus.

Thyrotropin modulates receptors for atrial natriuretic peptide on intact human thyroid cells

Interest in the mechanism of impaired salt and water metabolism in hypothyroidism has led to growing evidence of an interaction between atrial natriuretic peptide (ANP) and the thyroid, which includes reports of direct effects of thyroid hormone on ANP synthesis and circulating ANP levels, and of the presence of specific ANP receptors in human thyroid tissue, which may act to inhibit thyroglobulin (Tg) secretion. The authors questioned whether or not thyrotropin (TSH) has a role in this interaction. They used 125I-ANP to study the effect of TSH on ANP binding to human thyroid cells in primary culture. Binding competition by increasing concentrations of unlabeled ANP in the presence or absence of TSH was assessed by Scatchard analysis. At lower temperatures of 4 degrees C or 23 degrees C, TSH had no effect either on the ANP receptor equilibrium dissociation constant (Kd) or number of binding sites. However, at 37 degrees C, bovine TSH at 1 mU/ml reduced measurable binding sites by about 50% without affecting receptor affinity (Kd = 0.2 nM). Prolonged (6 days) coincubation of TSH with thyroid cells decreased the assayable ANP receptor. The effects of TSH appear to be specific because human luteinizing hormone, follicle-stimulatory hormone, growth hormone, human chorionic gonadotropin and iodide had no effect on ANP binding. Thus, human thyroid cells possess a single class of high-affinity, specific receptors for ANP with binding activity that is temperature dependent and modulated by TSH at physiologic temperature. TSH-mediated reduction of binding at 37 degrees C but not at 4 degrees C suggests an energy-dependent process that acts possibly by activating an ANP degradative enzyme or by changing the rate of receptor internalization and subsequent degradation.

Effect of atrial natriuretic factor (ANF) on nicotinic acetylcholine receptor channels in bovine chromaffin cells

Bovine chromaffin cells have binding sites for rat atrial natriuretic factor (ANF), as demonstrated autoradiographically by using the 125I-labelled peptide. Patch-clamp recording revealed that ANF reduces acetylcholine (ACh)-induced membrane currents in chromaffin cells at physiological membrane potentials. The effect was dose-dependent with the IC50 value being 5.2 microM ANF and the Hill coefficient close to 1. The channel block was absent at positive membrane potentials, indicating a non-competitive interaction of ANF with the open ACh receptor channel. Fragments of ANF had a much less pronounced action, which is possible due to their structure and molecular charge being different to ANF. The block of nicotinic ACh receptor channels may enable ANF to control the secretion of catecholamines from adrenal chromaffin cells.

Enhanced activity of the cardiac endocrine system during right ventricular hypertrophy

In a model of pulmonary hypertension induced by a single injection of monocrotaline (MCT), we observed a time-dependent right ventricular hypertrophy, which became apparent in treated rats 21 days after administration of MCT and progressed through day 45. Associated with this right ventricular hypertrophy were time-dependent increases in ventricular levels of immunoreactive atrial natriuretic peptide (iANP). Forty-five days after MCT treatment, treated rats exhibited a 72-fold increase in right ventricular iANP levels and a 7-fold increase in left ventricular iANP levels. Hybridization analysis of total RNA extracted from cardiac tissue indicated that both atrial and ventricular ANP mRNA levels were elevated in treated rats. These data suggest that during pulmonary hypertension and cardiac hypertrophy the endocrine activity of the heart expands to include ventricular tissue. ANP binding site autoradiography revealed decreased binding site density in the kidney and hearts of treated rats at 49 days, consistent with the occurrence of desensitization/down-regulation. Enhanced ventricular ANP production may serve as a compensatory response to sustained elevation of pulmonary arterial pressure or may function as an autocrine/paracrine system regulating cardiac function. In either case, the effects of augmented ANP production may be subject to modulation by the status of ANP receptors in target organs and cells.

Regulation of aldosterone receptor in rat kidney cytosol by atrial natriuretic factor

We investigated the effect of atrial natriuretic factor (ANF) on aldosterone receptors in the kidney cytosol, because the binding of aldosterone to aldosterone receptors in the cytosol is considered a critical step of its action. Rat atriopeptin III was injected into male Sprague-Dawley rats (200-250 g) via the femoral vein while under pentobarbital anesthesia, and aldosterone receptors in the kidney cytosol were determined. The maximum binding capacity and dissociation constant were calculated by the Scatchard analysis. Maximum binding capacity of both types of aldosterone receptor (Type I, high affinity and low binding capacity and Type II, low affinity and high binding capacity) gradually decreased after ANF injection, reached the lowest level after 2 hours, and then slightly recovered. When more than 2.5 micrograms/kg of rat atriopeptin III was injected, the density of aldosterone receptors significantly decreased. Injection of 12.5 micrograms/kg of rat atriopeptin III decreased maximum binding capacity of Type I receptor from 42.3 +/- 2.4 (mean +/- SD, n = 6) to 22.8 +/- 3.2 femtomole/mg protein (n = 6) (p less than 0.01), and that of Type II receptor decreased from 388 +/- 46 to 285 +/- 30 fmol/mg protein (p less than 0.01). Dissociation constant of both types of receptors did not change significantly after ANF injection. Plasma aldosterone concentration showed no significant change after ANF injection, and a significant change was noted after ANF administration on aldosterone receptors in the experiments on adrenalectomized rats 7 days after operation. Furosemide had no significant effect on aldosterone receptors in both normal and adrenalectomized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of atrial natriuretic peptide/cardiodilatin (ANP/CDD)-immunoreactivity in the salt gland of the Pekin duck

A novel peptide hormone, atrial natriuretic factor/cardiodilatin (ANP/CDD), was recently isolated and characterized from mammalian heart. Its presence has been demonstrated in several organs that contribute to water and sodium homeostasis, such as salivary glands. This study demonstrates the presence of ANP/CDD immunoreactivity in the salt gland of Pekin ducks by high performance liquid chromatography, radioimmunoassay and immunocytochemistry, using a specific antibody against atriopeptide I. A small number of distinct, ovoid or cuboid shaped ANP/CDD-immunoreactive cells were localized in the connective tissue surrounding and separating the central secretory tubules, whereas no immunostaining was observed in the peripheral tubules. Salt glands of ducks that were adapted to salt water revealed a significant hypertrophy of their secretory lobules. However, no differences were found between the number or localization of immunoreactive cells in the salt gland of salt water-acclimatized ducks and nonstimulated glands of ducks that were housed with ad libitum access to fresh water. Our results indicate that ANP/CDD may play a role in the regulation of sodium secretion in the salt gland of aquatic birds.

Direct binding of atrial natriuretic factor to adrenocortical mitochondria

Atrial natriuretic factor (ANF) is a known antagonist of adrenocortical aldosterone synthesis and secretion. Immunocytochemical and ultrastructural autoradiographic evidence suggests that ANF may bind to mitochondria of a number of target tissues including adrenal cortex. Consequently, the ability of [125I]ANF to bind directly to isolated bovine adrenocortical mitochondria was assessed. Mitochondrial-enriched subfractions of adrenocortical homogenates were prepared by differential and sucrose gradient centrifugation. Mitochondrial membranes specifically bound [125I]ANF. At 20 degrees C equilibrium was achieved between 90 and 120 min. [125I]ANF binding was inhibited in a concentration-dependent manner by unlabelled ANF (IC50 about 5 x 10(-10) M); other substances with biological actions on glomerulosa cells (arginine vasopressin, angiotensin II) did not alter [125I]ANF binding. Similarly shorter ANF fragments including ANF-(103-125), ANF-(99-109) and ANF-(111-126) had no significant competitive effect on binding of the labelled ligand. While Ca2+ and Mg2+ had little effect on ANF binding, the divalent cation Ni2+ inhibited binding of radiolabelled ANF by 90% (IC50 about 8.3 x 10(-5) M). Scatchard analysis revealed both high and low affinity binding sites for [125I]ANF with respective KDs of 4.7 +/- 7 pM and 0.3 +/- 0.02 nM and receptor densities of 1.1 +/- 0.2 and 8.6 +/- 0.1 pmol/mg protein. At 0.2 nM, Ni2+ caused a 5-fold and 100-fold decrease in high and low affinity [125I]ANF binding, respectively. The data demonstrate that ANF binds directly to mitochondria and perhaps it is at this site that the atrial peptide negatively modulates agonist-induced aldosterone biosynthesis.

Atrial natriuretic peptide levels during and after acute cardiac tamponade in dogs

The ability of the atrial wall to secrete atrial natriuretic peptide was studied in eight dogs during 2 h of cardiac tamponade and for 2 h after decompression of the pericardium. Cardiac tamponade was induced by instillation of 5% dextrose in water into the pericardial cavity until aortic systolic pressure was reduced by 30% to 35%. Heart rate, cardiac output and atrial, pericardial and aortic pressures were measured at 60 and 120 min of tamponade and at 5, 30, 60, 90 and 120 min after decompression. Blood samples were withdrawn at the same time for the determination of atrial natriuretic peptide and aldosterone levels. Aortic pressure decreased significantly during tamponade and increased after decompression to near control levels. Right and left atrial pressures as well as intrapericardial pressure increased significantly during tamponade and returned to control levels after decompression. The effective transmural pressure, which was reduced during tamponade, was increased significantly at 5 min after decompression. Cardiac output was significantly reduced during tamponade and returned to pretamponade levels after decompression. Over the total experimental period, no significant changes in the levels of atrial natriuretic peptide were observed, whereas aldosterone increased significantly. It is concluded that the increased atrial pressure observed during cardiac tamponade did not stimulate the secretion of atrial natriuretic peptide. Furthermore, atrial distension observed immediately after decompression was not sufficient or of long enough duration to induce measurable increases in atrial natriuretic peptide levels. Finally, the secondary hyperaldosteronism did not activate atrial natriuretic peptide secretion either during cardiac tamponade or after decompression.

Stimulatory effects of atrial natriuretic factor on phosphoinositide hydrolysis in cultured bovine aortic smooth muscle cells

The effects of atrial natriuretic factor (ANF) on phosphoinositide hydrolysis were examined in preparations of cultured bovine aortic smooth muscle cells. In homogenates or particulate fractions from cultured bovine aortic smooth muscle cells, ANF and atriopeptin I increased the formation of inositol phosphates and GTPase activity. The effects on inositol phosphates were markedly enhanced with guanosine 5'[gamma-thio]triphosphate. Both atrial peptides also stimulated the formation of diacylglycerol in intact cultured cells. In these experiments, atriopeptin I was about 10-fold more potent than ANF. These studies indicate that atrial peptides have stimulatory effects on phosphoinositide hydrolysis which are mediated through a guanine nucleotide regulatory protein. The greater potency of atriopeptin I on GTPase activity and the accumulation of inositol phosphates suggests that the nonguanylate cyclase-coupled receptor for ANF (ANF-R2) mediates the stimulatory effects of ANF on phosphoinositide hydrolysis through a guanine nucleotide regulatory protein.

Effects of physical exercise and anti-G suit inflation on atrial natriuretic factor plasma level

The purpose of this study was to measure the effect of enhanced venous return on atrial natriuretic factor (ANF) secretion during exercise and upright posture and the consequences on renin angiotensin aldosterone system (RAAS) activity. Six healthy male subjects were submitted to four different procedures. All procedures were performed in the same position, i.e. riding on a support with legs hanging. Two procedures were performed at rest: the subjects were studied after a 25-min rest in this position, with and without the lower limb fitted with an anti-G suit inflated to 60 mmHg. Two procedures were carried out with physical exercise; arm-cranking was performed in the same position with and without the anti-G suit inflated to 60 mmHg. Venous blood was collected before and after each procedure in order to measure plasma ANF, plasma aldosterone concentration (PAC), plasma renin activity (PRA), corticotrophin (ACTH) and catecholamine level. The data mean +/- SEM showed that the ANF plasma level decreased significantly (p less than 0.05) from 32.5 +/- 4 to 28 +/- 6 pg.ml-1 after a 20-min rest in the upright posture, whereas this effect was absolished with anti-G suit inflation. Physical exercise with and without the anti-G suit increased the ANF level above control values (60 +/- 13.6 pg.ml-1 and 53 +/- 13 pg.ml-1): anti-G suit inflation had no significant effect. PRA increased after rest in an upright posture and during physical exercise; anti-G suit inflation abolished this increase in both conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial and brain natriuretic peptides share binding sites in the kidney and heart

We examined the distribution of binding sites for atrial natriuretic peptide (ANP) and the recently discovered brain natriuretic peptide (BNP) in rat kidney and heart by receptor autoradiography. In frozen kidney sections, both 125I-ANP and 125I-BNP exhibited localized binding to cortical glomeruli. The binding of each radiolabeled peptide was abolished by inclusion of either excess (1 microM) unlabeled ANP or excess unlabeled BNP, suggesting that ANP and BNP share cortical glomerular binding sites. In frozen cardiac sections, ANP and BNP binding sites were localized to the endothelium of the endomural channels and endocardium. As was the case for kidney, binding of each peptide at these sites was abolished by the presence of excess unlabeled ANP or BNP, suggesting that these natriuretic peptides share binding sites in the heart as well. To explore further the possibility that ANP and BNP utilize the same receptor(s), we performed competitive binding experiments using cultured pulmonary artery endothelial (CPAE) cells. ANP and BNP competitively displaced one another with equivalent IC50 values from CPAE cell binding sites. Furthermore, both ANP and BNP elevated the levels of cGMP, a putative second messenger for ANP, in these cells. These data are consistent with the observation that BNP, like ANP, causes a natriuresis and diuresis in rats, and suggest that BNP may possess other biological activities known for ANP.

Atrial natriuretic factor inhibits angiotensin-induced aldosterone secretion: not through cGMP or interference with phospholipase C

ANF did not prevent the formation of [3H] inositol trisphosphate in response to AII but inhibited aldosterone secretion in calf adrenal glomerulosa cells. 8-bromo cGMP did not affect either inositol phosphate formation or aldosterone secretion. Changes in cytosolic Ca++ concentration induced by AII, as measured by Quin 2 fluorescence, were also unaffected by ANF. No difference in adrenal cell protein phosphorylation with AII or AII + ANF was observed. The results suggest that ANF may inhibit aldosterone secretion through a non-guanyl cyclase linked receptor system not involving the formation of phosphoinositide-derived second messengers. Interference with protein kinase C activity cannot be ruled out.

Natriuresis associated with elevated plasma atrial natriuretic hormone during supraventricular tachycardia

Elevated plasma levels of atrial natriuretic hormone (ANH) have been found in patients during paroxysmal supraventricular tachycardia (SVT) and other clinical syndromes. However, physiologic effects of this endogenous ANH have not been demonstrated. To determine whether the rise in ANH during SVT is associated with either a natriuresis or kaliuresis, urine sodium and potassium levels were measured in five patients at baseline and during SVT simulated by rapid atrioventricular pacing. Plasma ANH levels increased from 149 +/- 35 pmol/L at baseline to 187 +/- 31 pmol/L (p = 0.007) during SVT. Plasma vasopressin and renin levels were unchanged. Urine sodium levels increased 49% from 1.54 +/- 0.66 mEq/hr at baseline to 2.29 +/- 0.89 mEq/hr (p = 0.044) during SVT, and urine potassium levels increased 22% from 4.14 +/- 0.10 mEq/hr to 5.04 +/- 1.25 mEq/hr (p = 0.018). Urine sodium and potassium levels returned to baseline values 1 hour after pacing. Thus elevated plasma levels of ANH during SVT are associated with both a natriuresis and kaliuresis, which may represent physiologic effects of the endogenously secreted hormone.

Localization of the atrial natriuretic peptide binding sites in the inner ear tissue--possibly an additional regulating system

Specific high affinity atrial natriuretic peptide (ANP) binding sites were identified and localized by autoradiography (125J-ANP 1-28) in the inner ear of guinea pigs. ANP is a cardiac hormone known to mediate increased capillary permeability, vasodilation, and natriuresis. Since specific receptors for ANP exist in both eye and brain, possibly playing a role in regulation of fluid and pressure (14, 15), we hypothetized that ANP might be involved also in inner ear fluid dynamics via interaction with other volume/electrolyte balance regulating hormones including vasopressin, renin, and aldosteron. The distribution of ANP receptor in the inner ear tissue appears unequal, which may play a significant role in view of some functional disturbances such as Meniere's disease.

Plasma concentrations of atrial natriuretic factor in normal pregnancy and early puerperium

The atrial natriuretic factor (ANF) and parameters related to renal sodium handling and renal function were evaluated in 92 normotensive pregnant women at different gestational ages (1st group: 7th-13th week, 2nd group: 14th-20th week; 3rd group: 21st-27th week; 4th group: 28th-34th week; 5th group: greater than 34th week), in 15 normotensive non-pregnant women and in 15 normotensive women 6 days after spontaneous delivery at the end of a normal pregnancy. ANF did not differ significantly between the 5 groups of pregnant women while, concurrently with a further increase in plasma volume (as shown by our data) it was significantly higher in late pregnancy (3rd and 5th groups) than in the non-pregnant women. ANF in post-partum women was significantly higher than in non-pregnant and pregnant women. Only in post-partum women was ANF significantly directly related to sodium excretion. Even though ANF does not seem to play an important role in water and sodium excretion in pregnancy in comparison with other hormones such as progesterone, oestriol and aldosterone, the higher levels of ANF in late pregnancy probably represent a compensatory increase when a given threshold of plasma volume (and therefore of atrial stretch) is reached. However ANF does seem to play a more important role in the induction of diuresis and natriuresis in early puerperium.

Presence of immunoreactive atrial natriuretic peptide in follicular fluid, ovary and ovarian perfusates

Immunoreactive atrial natriuretic peptide (ir-ANP) was measured in the follicular fluid of pig ovarian follicle, and rabbit ovarian homogenates and perfusates using a specific radioimmunoassay (RIA). Serial dilution curves made with the extracts of follicular fluid, ovarian homogenates and perfusates using SepPak C18 cartridges were parallel with the RIA standard curve. On gel filtration chromatography and reverse phase HPLC, all extracted materials showed high and low molecular weight forms of ir-ANP. The amount of ir-ANP in rabbit ovary was 40.70 +/- 0.39 pg/mg and that in follicular fluid of pig ovarian follicle was 18.88 +/- 2.49 pg/ml.

Receptors for atrial natriuretic peptide (ANP) and regulation of thyroglobulin secretion by ANP in human thyroid cells

Specific binding sites for atrial natriuretic peptide (ANP) were identified and characterized in primary cultures of human thyroid cells. Saturation analysis using [125I] alpha rat ANP as the ligand showed a single class of high affinity binding (Kd = 0.2 nM) which was inhibited by atriopeptin I and the alpha -human form of ANP, but not by a C-terminal fragment of the peptide. The number of ANP binding sites in these cultures was not altered by the thyroid hormone concentration of the medium. In a dose-response experiment, thyro-globulin secretion was significantly reduced in the presence of 0.01 nM ANP and was maximally reduced (to 25% of control value) with 10 nM ANP. Cyclic GMP production was increased threefold in the presence of 100 nM ANP, but was unchanged with lower doses (0.01 and 0.1 nM) of the peptide. The finding of receptors in thyroid follicular cells suggests a hitherto unrecognized role of ANP in the thyroid gland.

Effect of ANP on sustained aldosterone secretion stimulated by angiotensin II

The sustained aldosterone secretory response to angiotensin II (ANG II) depends on receptor-mediated increases in membrane diglyceride (DG) and an increase in calcium influx rate. These signals serve to activate membrane-associated protein kinase C (PKC) and result in enhanced phosphorylation of a unique set of proteins. These events can be mimicked by the addition of a phorbol ester, 12-O-tetra decanoyl phorbol 13-acetate (TPA), and a calcium ionophore, A23187, that bypass the initial receptor-associated events. We studied the inhibitory action of atrial natriuretic peptide (4-28 hANP) on the sustained secretory response to ANG II in isolated bovine adrenal glomerulosa cells. Although 10 nM ANP inhibited aldosterone secretion, it did not significantly alter the ANG II-elicited rise in 45Ca2+ influx rate [control (CON): 0.44 +/- 0.06; ANG II: 1.11 +/- 0.12 (P less than 0.001); ANG II + ANP: 1.18 +/- 0.14], the steady-state level of aequorin luminescence [intracellular [Ca2+] ([Ca2+]i)], or the rise in cellular DG content [CON: 0.132 +/- 0.01; ANG II: 0.194 +/- 0.01 (P less than 0.005); ANG II + ANP: 0.202 +/- 0.01 nmol/10(6) cells]. IN addition, ANP was able to inhibit aldosterone secretion stimulated by the combined addition of A23187 + TPA. When protein phosphorylation in the ANP-inhibited cells was evaluated, ANG II-induced protein phosphorylation events were preserved. In contrast to the effect of ANP, the calcium channel blocker nitrendipine abolished the ANG II-induced rise in 45Ca2+ influx rate, reduced the steady-state level of [Ca2+]i, and returned the phosphoproteins to their control states.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of posture on the plasma levels of atrial natriuretic factor

Atrial natriuretic factor (ANF) is a peptide with potent natriuretic, diuretic and vasorelaxant activities. Stretching of the right atria causes release of ANF into the circulation. Therefore, changes in central blood volume or acute volume expansion are likely to change the plasma levels of ANF. In this study we investigated the effects of changes in posture on the plasma levels of ANF, plasma renin activity (PRA) and plasma aldosterone (aldo). Eight male and five female volunteers ranging in age from 23 to 26 years were placed on a normal sodium intake and on the experimental day blood was obtained for ANF, PRA, and aldo after 30 minutes of lying supine, 30 minutes of 10 or 20 degrees head-down tilt, and 30 minutes of standing. Plasma ANF increased significantly after 30 minutes of head-down tilt from the supine value of 33.7 +/- 5.2 pg/ml to 47.7 +/- 7.7 pg/ml (p less than 0.02) and suppressed to 14.1 +/- 0.02) after 30 minutes of standing. PRA did not change significantly with head-down tilt, (supine 1.64 +/- 0.44 ngAI/ml/h vs. 30 minutes tilt 1.28 +/- 0.32 ngAI/ml/h (p = NS). Plasma aldosterone decreased by head-down tilt from 11.2 +/- 1.2 ng/ml to 8.4 +/- 0.8 ng/dl (p less than 0.02) and returned to the supine level after standing. In conclusion ANF levels change significantly with posture. Increase in central blood volume by head-down tilt increases ANF levels and suppresses plasma aldosterone with no effect on PRA. Standing decreases ANF significantly. These results suggest that for proper interpretation of plasma levels of ANF, posture at the time of sampling has to be standardized.

Rapid reduction of plasma atrial natriuretic peptide levels during percutaneous transvenous mitral commissurotomy in patients with mitral stenosis

To clarify the direct contribution of the left atrial pressure to secretion of human atrial natriuretic peptide (hANP), we have attempted to study the relations between plasma hANP levels, neurohumoral factors, and hemodynamic changes in 13 patients with mitral stenosis undergoing percutaneous transvenous mitral commissurotomy (PTMC). After PTMC, the left atrial pressure fell from 14.7 +/- 1.9 (mean +/- SEM) to 6.5 +/- 0.7 mm Hg in all patients studied (p less than 0.0005), whereas there were no remarkable changes in either the right atrial pressure, mean arterial pressure, or heart rate. Plasma immunoreactive hANP levels obtained from the pulmonary artery decreased from 278 +/- 51 to 137 +/- 31 pg/ml after PTMC (p less than 0.0005). There was a significant correlation between the decrement of hANP levels and that of left atrial pressure (r = 0.72, p less than 0.005). Neither plasma renin activity nor norepinephrine levels changed. In contrast, plasma aldosterone concentrations significantly increased from 11.3 +/- 1.5 to 16.4 +/- 2.7 pg/ml after PTMC (p less than 0.01), although there was no casual relation between plasma concentrations of aldosterone and hANP. The present result with PTMC-induced rapid fall of the left atrial pressure with a concomitant reduction in hANP secretion strongly suggests the importance of the left atrial pressure on hANP secretion in humans.

Atrial natriuretic peptide in the central nervous system of the rat

1. Studies of the presence of atrial natriuretic peptide immunoreactivity and receptor binding sites in the central nervous system have revealed unusual sites of interest. 2. As a result, numerous studies have appeared that indicate that brain atrial natriuretic peptide is implicated in the regulation of blood pressure, fluid and sodium balance, cerebral blood flow, brain microcirculation, blood-brain barrier function, and cerebrospinal fluid production. 3. Alteration of the atrial natriuretic peptide system in the brain could have important implications in hypertensive disease and disorders of water balance in the central nervous system.

Localization of 125I-labelled alpha-r-atrial natriuretic peptide in rat tissues by whole-body and microautoradiography

125I-labelled alpha rat atrial natriuretic peptide (28 amino acids: Ser 99-Tyr 126) ([125I]alpha-rANP) was given i.v. to Sprague-Dawley rats and the distribution of radioactivity in the tissues was examined by whole-body and microautoradiography at intervals from 2 min to 4 h after the administration. Inhibition of uptake of the [125I]alpha-rANP by simultaneous injection of an excess of non-labelled alpha-rANP was taken as an indication that highly labelled structures in rats injected with [125I]alpha-rANP alone are due to an abundance of specific receptors for the peptide. In the rats given only the [125I]alpha-rANP a rapid and high radioactivity occurred in the renal glomeruli, the endocardium of the heart ventricles, the endothelium of the processus ciliares of the eyes, the portal vessels and a few larger vessels of the liver, the subcapsular vessels of the adrenal glands and the parenchyma of the lungs. Other tissues showing a distinct, but less prominent, radioactivity were the endocardium of the heart atria, the walls of the great afferent and efferent vessels in the thoracic cavity, the choroid plexuses of the brain ventricles, the pia mater, brown fat, the muscularis layer of the stomach and the intestines, the lamina propria of the villi in the small intestine and the walls of a few small blood vessels in the kidney medulla. The specific labelling was highest at 2 min after injection and then diminished at later intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the gene for the atrial natriuretic peptide in cardiac myocytes in vitro

Primary cultures of neonatal cardiocytes express the gene for atrial natriuretic peptide (ANP). In general the levels of expression follow the rank order: atrial greater than ventricular much greater than nonmyocardial cells. Following the initial dispersion cardiocytes require 48 to 72 hours before ANP secretion and ANP mRNA accumulation approach a new steady-state level. In situ hybridization analysis indicates that ANP gene expression is concentrated in a subpopulation of cardiocytes in both the atrial and the ventricular cell cultures. These findings suggest that these primary cultures may be of value in defining the factors governing the expression of the ANP gene in the cardiac cell.

Regulation of receptors for atrial natriuretic peptide in the rat and human

Atrial natriuretic factor or peptide (ANP) is a peptide recently isolated from mammalian atria with potent natriuretic, vasorelaxant, and aldosterone-inhibitory properties. ANP may play an important role in the regulation of blood pressure and body salt and fluid balance. The presence of binding sites for ANP in the vasculature and adrenal glomerulosa of rats and in platelets in humans has been demonstrated. These sites are involved in the mediation of the vasorelaxant effect of ANP and its inhibitory action on aldosterone secretion. The role of binding sites on platelets is unknown, but the availability of platelets makes them a useful model for investigating the regulation of receptors for atrial natriuretic factor in humans. The effect of sodium depletion and loading and mineralocorticoids on the density of rat vascular and adrenal sites for ANP was examined, as well as changes that occur after development of renovascular and DOCA-salt hypertension in rats. Sodium loading in the presence of reduced renal mass (unilateral nephrectomy) or mineralocorticoid administration produced renin suppression and resulted in down-regulation of vascular ANP receptors. In one-kidney, one-clip Goldblatt hypertensive rats and in DOCA-salt hypertensive rats, two models of volume-expanded, non-renin-dependent experimental hypertension, the density of ANP binding sites in the mesenteric arterioles was significantly decreased. The sensitivity to ANP of precontracted aorta from renovascular and mineralocorticoid hypertensive rats was significantly reduced. No consistent changes occurred in the density of ANP binding sites in the adrenal glomerulosa.(ABSTRACT TRUNCATED AT 250 WORDS)