Atrial natriuretic factor inhibits the hypertension induced by chronic infusion of norepinephrine in conscious rats

Hyperosmotic and thermal stresses activate p38-MAPK in the perfused amphibian heart

We assessed the activation of p38-MAPK (mitogen-activated protein kinase) by osmotic and thermal stresses in the isolated perfused amphibian (Rana ridibunda) heart. Hyperosmotic stress induced the rapid activation of the kinase. In particular, in the presence of 0.5 mol l–1 sorbitol, p38-MAPK was maximally phosphorylated (by approximately twelvefold) at 15 min, while excess of NaCl (206 mmol l–1 final concentration) or KCl (16 mmol l–1 final concentration) stimulated a less potent activation, maximised (by approximately eightfold and fourfold) within 2 min and 30 s, respectively, relative to control values. The effect of all three compounds examined was reversible, since the kinase phosphorylation levels decreased upon reperfusion of the heart with normal bicarbonate-buffered saline. Conversely, hypotonicity did not induce any p38-MAPK activation. Furthermore, both hypothermia and hyperthermia induced considerable phosphorylation of the kinase, by four- and 7.5-fold, respectively, relative to control values. Immunohistochemical studies elucidated the localisation pattern of phospho-p38-MAPK and also revealed enhanced atrial natriuretic peptide (ANP) immunoreactivity in osmotically stressed hearts. Interestingly, SB 203580 (1 μmol l–1) not only completely blocked the activation of p38-MAPK by all these interventions, but also abolished the enhanced ANP immunoreactivity induced by 0.5 mol l–1 sorbitol. These findings indicate the possible involvement of ANP in the mechanisms regulating responses under such stressful conditions.

ANP in regulation of arterial pressure and fluid-electrolyte balance: lessons from genetic mouse models

The recent development of genetic mouse models presenting life-long alterations in expression of the genes for atrial natriuretic peptide (ANP) or its receptors (NPR-A, NPR-C) has uncovered a physiological role of this hormone in chronic blood pressure homeostasis. Transgenic mice overexpressing a transthyretin-ANP fusion gene are hypotensive relative to the nontransgenic littermates, whereas mice harboring functional disruptions of the ANP or NPR-A genes are hypertensive compared with their respective wild-type counterparts. The chronic hypotensive action of ANP is determined by vasodilation of the resistance vasculature, which is probably mediated by attenuation of vascular sympathetic tone at one or several prejunctional sites. Under conditions of normal dietary salt consumption, the hypotensive action of ANP is dissociated from the natriuretic activity of the hormone. However, during elevated dietary salt intake, ANP-mediated antagonism of the renin-angiotensin system is essential for maintenance of blood pressure constancy, inasmuch as the ANP gene "knockout" mice (ANP -/-) develop a salt-sensitive component of hypertension in association with failure to adequately downregulate plasma renin activity. These findings imply that genetic deficiencies in ANP or natriuretic receptor activity may be underlying causative factors in the etiology of salt-sensitive variants of hypertensive disease and other sodium-retaining disorders, such as congestive heart failure and cirrhosis.

Distribution of immunoreactive atrial and brain natriuretic peptides in the heart of the chicken, quail, snake and frog

The distribution of atrial natriuretic peptide (ANP)- and brain natriuretic peptide (BNP)-granules was examined immunohistochemically and ultrastructurally in the hearts of the chicken, Japanese quail, Japanese rat snake and bull-frog. Moreover, natriuretic peptide (NP)-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, ANP-immunoreactivity (IR) was not detected in any cardiocytes, but BNP-IR was detectable in most atrial and ventricular cardiocytes of both chicken and quail. In the snake, ANP-IR was seen in most atrial and ventricular cardiocytes, which showed traces and negative in BNP-IR, respectively. Both ANP- and BNP-IR were detected in the atrial and ventricular cardiocytes in the frog. Ultrastructurally, most of NP-granules were found in the perinuclear region in the chicken, quail and snake atrium, but the frog atrial cardiocytes had granules generally dispersing widely in the cell. By ultrastructural morphometry, the number of granules in the atrial cardiocyte was greatest in the frog, followed by the snake, and chicken or quail, in this order. The diameter of granules in the atrial cardiocyte was largest in the snake and reduced via the frog to the chicken or quail. In the ventricular cardiocytes of all species, the number and size of granules were significantly less than that in the atrial ones. These results indicated that the hearts of the chicken and quail contain only BNP, and that there are two different natriuretic peptides, ANP and BNP, in the snake and frog hearts.

Atrial natriuretic peptide and its potential role in pharmacotherapy

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

Effects of cicletanine on the urinary excretion of prostanoids and kallikrein, and on renal function in man

The effects of cicletanine, a new antihypertensive agent, on the prostaglandin-kallikrein system and the renin-angiotensin system were studied. A single oral dose of 200 mg cicletanine or placebo was administered to 9 healthy male volunteers, with samples of blood and urine obtained before and 2 hours after drug administration. Cicletanine increased the urine flow, urinary excretion of sodium, and fractional excretion of sodium by 47%, 115%, and 104%, respectively. While the excretion of 6-keto-prostaglandin-F1 alpha was enhanced significantly, urinary excretion of thromboxane-B2, prostaglandin-E2, and kallikrein were unchanged. Cicletanine also did not alter plasma renin activity, plasma aldosterone concentration, or creatinine clearance. These observations suggest that cicletanine may suppress sodium reabsorption at the nephron, and it may stimulate prostacyclin generation with no effect on that of thromboxane-A2. Thus cicletanine may be beneficial in the management of cardiovascular disorders in which the equilibrium between prostacyclin and thromboxane is disturbed.

Endothelin-1 augments pressor response to angiotensin II infusion in rats

To assess possible roles of endothelin in the regulation of blood pressure, we studied effects of a subpressor dose of endothelin-1 (3 micrograms/kg/day) on chronic blood pressure responses to infusion of angiotensin II and norepinephrine in rats. Rats were infused with angiotensin II at a subpressor dose (400 micrograms/kg/day i.p.) or with norepinephrine at a subpressor dose (360 micrograms/kg/day i.p.) for 6 days. Systolic blood pressure was significantly elevated during combined infusion of endothelin-1 and angiotensin II, whereas endothelin-1 alone or angiotensin II alone failed to induce any significant changes in systolic blood pressure compared with vehicle alone. This effect was sustained for the whole experimental period and was not associated with any significant changes in body weight, fluid intake, urine volume, or urinary electrolyte excretion. In contrast, combined infusion of endothelin-1 and norepinephrine failed to elevate systolic blood pressure, and no significant difference in systolic blood pressure was observed for the whole experimental period among the four groups of rats with endothelin-1 in combination with norepinephrine, endothelin-1 alone, norepinephrine alone, and vehicle alone. The present results indicate that angiotensin II and endothelin-1, but not norepinephrine and endothelin-1, work synergistically to raise the blood pressure and also suggest the possibility that endothelin-1 may modulate blood pressure control.

Atrial natriuretic peptide and parathyroid hormone (1-84) in relation to noradrenaline induced changes in blood pressure in uraemic and healthy subjects

In order to evaluate the hormonal regulation of blood pressure (BP) in uraemia 12 patients on chronic maintenance dialysis and 14 healthy controls were studied. BP and plasma concentrations of atrial natriuretic peptide (ANP), cyclic 3',5'-guanosine monophosphate (cGMP), and intact parathyroid hormone (PTH(1-84)) were determined before, during, and after a 60 min noradrenaline infusion 0.1 micrograms kg-1 body wt. min-1. Mean BP increased to the same extent in the uraemic patients (median 15 mmHg, range 6-25 mmHg) as in the controls (12 mmHg, 5-25 mmHg). ANP increased during noradrenaline infusion both in patients (7.2 to 8.3 pmol/l, medians, p < 0.01) and in controls (4.4 to 6.0 pmol/l, p < 0.01), and so did cGMP (patients: 31.6 to 35.9 nmol/l, p < 0.05; controls: 6.6 to 8.7 nmol/l, p < 0.01). PTH(1-84) was higher in the uraemic patients than in the controls, but was unchanged during noradrenaline infusion in both groups. Correlation analyses gave no evidence of a direct relation between BP and ANP, but basal PTH(1-84) was negatively correlated to basal mean BP in the patients (rho = -0.615, p < 0.05), but not in the controls. In conclusion, noradrenaline induced similar elevations of BP in dialysis patients as in healthy controls despite elevated ANP and PTH(1-84) in the patients, and ANP release was stimulated in both groups. PTH(1-84) may participate in blood pressure regulation in uraemic patients.

Central interaction between endothelin and brain natriuretic peptide on pressor and hormonal responses

Interaction between intracerebroventricular (i.c.v.) administration of endothelin (ET) and brain natriuretic peptide (BNP) on pressor and hormonal responses was examined in unanesthetized, freely moving rats. I.c.v. administered ET (5, 20 or 40 pmol/2 microliters) dose-dependently increased arterial pressure. Plasma catecholamine levels were elevated by 40 pmol of ET, and plasma ACTH level was also elevated by centrally administered ET in a dose-dependent manner. I.c.v. administration of BNP (0.2, 1 nmol/3 microliters) dose-dependently attenuated central ET (40 pmol/2 microliter)-induced pressor response, plasma catecholamine and ACTH secretion. These results indicate that ET may be one of the neuropeptides which stimulate both sympathetic nervous system and hypothalamo-pituitary-adrenal axis, and that BNP and ET interact in the central nervous system (CNS) to regulate cardiovascular and hormonal functions. Furthermore, these results raise a possibility that BNP antagonizes the effect of not only angiotensin II but also other neuropeptides in the CNS.

Atrial natriuretic factor prevents NaCl-sensitive hypertension in spontaneously hypertensive rats

Our previous studies demonstrated that acute infusion of atrial natriuretic factor (ANF) produces an enhanced depressor response in NaCl-sensitive spontaneously hypertensive rats (SHR-S) fed a high (8%) NaCl diet compared with control SHR-S fed a normal (1%) NaCl diet and that dietary NaCl loading increases circulating ANF levels in Wistar-Kyoto (WKY) rats but not in SHR-S. The current study tested the hypotheses that 1) long-term infusion of ANF at a dose that elevates plasma ANF to levels comparable with those seen in high NaCl-fed WKY rats prevents the NaCl-induced exacerbation of hypertension in SHR-S and 2) ANF lowers blood pressure in this model by a sympatholytic effect. Male SHR-S received infusions of ANF (0.1 microgram/hr) or vehicle intravenously via osmotic minipump for 3 weeks beginning immediately before initiation of 1% or 8% NaCl diets at age 7 weeks. Chronic ANF infusion prevented the increase in arterial pressure in response to a high NaCl diet in SHR-S but had no effect in 1% NaCl-fed SHR-S. Thus, the NaCl-sensitive component of hypertension in SHR-S was more sensitive to ANF than the non-NaCl-sensitive component. Plasma norepinephrine was significantly increased in ANF-treated, 8% NaCl-fed SHR-S compared with vehicle controls, suggesting that ANF did not prevent NaCl-sensitive hypertension by a sympatholytic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor is a new neuromodulatory peptide

In this commentary, we will briefly discuss the potential regulatory role of atrial natriuretic factor in peripheral autonomic nervous system function. The focus will be on atrial natriuretic factor's involvement in cardiovascular homeostasis through its peripheral effect on sympathetic nervous activity, which may complement its humoral role. [Kuchel et al. (1987) Life Sci. 40, 1545-1551; Lang et al. (1985) Nature 314, 264-266]. We will attempt to support the hypothesis of its neuromodulatory action on efferent autonomic outflow. Specifically, the role of atrial natriuretic factor in the regulation of the synthesis and release of neurotransmitters and in synaptic transmission at the level of the sympathetic ganglia will be outlined. Its potential usefulness in neurobiological studies will also be indicated.

Enkephalinase (EC 3.4.24.11) inhibitors: protection of endogenous ANF against inactivation and potential therapeutic applications

Atrial natriuretic factor (ANF) is a cardiac hormone exerting potent cardiovascular and renal effects but its poor intestinal absorption and rapid inactivation have prevented so far its therapeutic utilisation. However inhibition of endogenous ANF metabolism progressively emerges as a novel therapeutic approach in cardiovascular and renal disorders. The critical role played by enkephalinase (membrane metalloendopeptidase, EC 3.4.24.11) in ANF inactivation was deduced from the effects of inhibitors. These compounds not only protect partially exogenous ANF from hydrolysis by some tissue preparations in vitro but also, in vivo, they increase the half-life of the exogenous hormone in plasma and, even more markedly, its recovery in intact form in kidney, a major target organ. In addition, enkephalinase inhibitors increase by two- to three-fold the circulating level of endogenous ANF, even when the latter is already markedly elevated, such as in patients with chronic heart failure. Finally, enkephalinase inhibitors induce a series of ANF-like responses such as natriuresis, diuresis or increase in cGMP excretion which are attributable to the hormone. These pharmacological observations, as well as preliminary clinical trials, suggest that enkephalinase inhibitors may represent a novel class of therapeutic agents with potential applications in congestive heart failure, essential hypertension and various sodium-retaining states.

[Atrial natriuretic peptide and its significance for arterial hypertension]

Atrial natriuretic peptide is a recently discovered cardiac hormone with natriuretic, vasodilatory and hypotensive activities. The role of this hormone in the pathophysiology of hypertension is of particular interest. In contrast to an earlier concept, a deficiency of the atrial peptide could not be found in animal models of hypertension or in patients. ANP plasma levels were elevated in SHR with accelerated hypertension, in salt-sensitive Dahl rats, in rats with DOCA-salt-hypertension and in animals with renovascular hypertension. Elevated ANP levels under these conditions can be explained by an expansion of the intravascular volume or by an elevated atrial wall stretch induced by the hypertension itself. In patients with primary hypertension, plasma levels of the peptide are raised in some patients and are normal in others. Plasma ANP levels correlate with age, blood pressure and signs of left ventricular hypertrophy. A negative correlation is described between ANP and renin. Measurement of plasma ANP levels does not allow a differentiation between primary and secondary forms of hypertension. Elevated ANP levels are also found in primary hyperaldosteronism and in renal failure. Stimulation of ANP secretion by physical exercise and dietary salt loading is maintained in hypertension. Infusion of 1-28-hANP leads to a reduction in systemic arterial pressure in normotensives and hypertensives. The natriuresis induced by exogenous ANP is more pronounced in hypertensives. Stimulation of endogenous ANP secretion does not prevent the rise in blood pressure possibly due to a reduction in ANP receptors in target tissues.

Chronic blockade of endogenous atrial natriuretic polypeptide (ANP) by monoclonal antibody against ANP accelerates the development of hypertension in spontaneously hypertensive and deoxycorticosterone acetate-salt-hypertensive rats

To explain the pathophysiological significance of endogenous atrial natriuretic polypeptide (ANP) in the development of hypertension, we examined the effect of chronic, repetitive administrations of MAb raised against alpha-rat ANP in two rat models of hypertension, spontaneously hypertensive rats of the stroke prone substrain (SHR-SP), and deoxycorticosterone acetate (DOCA)-salt rats. Weekly intravenous administrations of MAb with high affinity for alpha-rat ANP, named KY-ANP-II (MAb[KY-ANP-II]), started at the age of 6 wk, significantly augmented the rise in blood pressure of SHR-SP, compared with control SHR-SP treated with another MAb with quite low affinity for alpha-rat ANP, named KY-ANP-I (MAb[KY-ANP-I]), throughout the observation period. The administrations of MAb[KY-ANP-II] had no significant effect on blood pressure of age-matched normotensive Wistar Kyoto rats, compared with those receiving MAb[KY-ANP-I]. Weekly administrations of MAb[KY-ANP-II] also significantly aggravated hypertension in DOCA-salt rats. Blood pressure of DOCA-salt rats treated with MAb[KY-ANP-II] was significantly higher than that of DOCA-salt rats treated with MAb[KY-ANP-I] throughout 8 wk of DOCA and 1% saline administration. The administration of MAb[KY-ANP-II] also significantly attenuated exaggerated diuresis and natriuresis in DOCA-salt rats compared with those treated with MAb[KY-ANP-I]. Elevated plasma cGMP levels of both SHR-SP and DOCA-salt rats were significantly reduced by the administration of MAb[KY-ANP-II]. These results suggest the compensatory role of augmented secretion of ANP in these hypertensive rats and support the concept that augmented secretion of ANP could represent an antihypertensive deterrent mechanism.

Evidence against the central nervous system being involved in altered reflex control of sympathetic nerve activity by atrial natriuretic peptide

This study aimed to examine whether atrial natriuretic peptide (ANP) alters arterial baroreceptor control of sympathetic nerve activity (SNA) by acting on the CNS. In rabbits anesthetized with alpha-chloralose, we examined changes in arterial pressure and renal SNA in response to graded electrical stimulation (1.7, 3.3, 5.0 Hz) of aortic depressor nerves during the i.v. infusion of saline or alpha-human atrial natriuretic peptide (alpha-hANP) (0.1, 1.0 microgram/kg/min) or after the i.c.v. injections of saline or alpha-hANP (3, 10 micrograms). Sinoaortic denervation and bilateral vagotomy were done before examination in all rabbits to eliminate the influence of the known effects of ANP on arterial and cardiac receptors. I.v. alpha-hANP decreased arterial pressure but did not alter renal SNA. I.c.v. alpha-hANP did not change arterial pressure or renal SNA. Arterial pressure and renal nerve responses to graded electrical stimulation of aortic depressor nerves were not altered by i.v. or i.c.v. alpha-hANP. These results suggest that alpha-hANP does not modulate control of renal SNA by acting on the CNS.

Plasma atrial natriuretic polypeptide as an index of left ventricular end-diastolic pressure in patients with chronic left-sided heart failure

To evaluate the relationship between plasma atrial natriuretic polypeptide (ANP), hemodynamic parameters, and plasma catecholamines and, in addition, to determine whether circulating ANP is metabolized in the pulmonary circulation, plasma concentrations of ANP were determined in 40 patients with chronic left-sided heart failure. After at least 30 minutes of bed rest with the patient in the supine position, blood samples were drawn simultaneously from both the main pulmonary artery (mPA) and the ascending aorta (Ao) before administration of contrast medium. The plasma ANP concentrations significantly decreased from the mPA to the Ao (135.3 +/- 18.1 pg/ml vs 127.4 +/- 19.4 pg/ml; mean +/- SEM, p less than 0.05). The plasma ANP level in the mPA correlated with the plasma norepinephrine level in the Ao (r = 0.71, p less than 0.01), right atrial pressure (r = 0.34, p less than 0.05), mean pulmonary capillary wedge pressure (r = 0.829, p less than 0.001), and left ventricular end-diastolic pressure (LVEDP) (r = 0.88, p less than 0.001). Of the various hemodynamic parameters and plasma catecholamine concentrations in the Ao, only LVEDP was found to be an independent and significant predictor of plasma ANP levels in the mPA. These results indicate that ANP released from the heart is regulated mainly by preload (LVEDP) in cases of left-sided heart failure and that circulating ANP is metabolized in the pulmonary circulation. In conclusion, the plasma ANP concentration may be a useful noninvasive index of LVEDP in patients with chronic left-sided heart failure.

Atrial natriuretic peptide

This report has reviewed some of the cardiovascular aspects of ANP. The emergence of the heart as an endocrine organ requires that numerous questions be asked with regard to the importance of ANP to anesthesia and surgery. It is clear that the interaction of the hormone with other vasoactive compounds, including anesthetic agents, requires further elucidation. The accumulation of more information regarding the regulation of ANP and its cardiovascular setting will define its role in hemodynamic homeostasis in the acute clinical setting. Questions of specific interest to the anesthesiologist that require elucidation are: (1) Does the presence of abnormal ANP levels, associated with specific disease states, affect perioperative cardiovascular function? (2) Do cardiac surgery and CPB affect ANP-adrenergic interaction? (3) What is the relationship among blood volume, blood pressure, cation metabolism, and the ANP-renin-angiotensin system in perioperative patients? (4) What is the role of ANP as a therapeutic modality in surgical patients?

Physiological responses to low dose infusions of atrial peptide in conscious dogs

Mongrel dogs prepared with chronic catheters in their femoral artery and vein and urinary bladder received 60 minute infusions of atrial peptide ranging from 5 to 100 ng/kg/min. Infusion of atrial peptides caused dose dependent increases in plasma atrial peptide concentration with doses of 25 ng/kg/min or less increasing plasma concentrations to levels observed in normal animals during stimulation of endogenous atrial peptide secretion. Atrial peptide infusion at doses of 10 ng/kg/min and above caused significant decreases in mean arterial pressure which were not accompanied by statistically significant changes in heart rate. Atrial peptide infusion at doses of 25 ng/kg/min and above increased urinary sodium excretion and urine flow rate. Atrial peptide infusion was without effect on plasma vasopressin, ACTH and corticosterone concentrations. However, atrial peptide infusion resulted in dose dependent decreases in plasma aldosterone concentration and plasma renin activity, but the decreases were only significant with the high physiologic (25 ng/kg/min) and pharmacologic doses (50 & 100 ng/kg/min). These data show that atrial peptide infusions in conscious dogs have minimal effects when infused in small doses that mimic endogenous atrial peptide release. At higher doses, significant effects on the cardiovascular, renal and endocrine systems can be observed but their physiological significance is unclear.

Role of thromboxane A2 in the hypotensive effect of captopril in essential hypertension

We have previously reported that captopril stimulates thromboxane A2 synthesis in patients with essential hypertension. In the present study, the hypotensive effects of captopril and OKY-046, a selective inhibitor of thromboxane A2 synthetase, were studied in nine patients with essential hypertension to determine whether thromboxane A2 is involved in the regulation of blood pressure. A single oral dose of OKY-046 (400 mg) decreased urinary thromboxane B2 (a stable metabolite of thromboxane A2) excretion significantly (from 113 +/- 19.0 to 51.0 +/- 6.1 pg/min; p less than 0.01) and increased urinary sodium excretion significantly (from 73.0 +/- 15.3 to 113.0 +/- 14.4 microEq/min; p less than 0.01), but no change was observed in mean arterial pressure. The administration of OKY-046 (600 mg/day) for 3 days induced a significant and sustained decrease in urinary thromboxane B2 excretion, but it did not affect the mean arterial pressure. Although captopril (50 mg) alone induced a significant increase in urinary thromboxane B2 excretion (from 91.4 +/- 11.0 to 297.3 +/- 30.8 pg/min; p less than 0.001) and a significant decrease in mean arterial pressure (from 97.0 +/- 4.7 to 88.1 +/- 5.1 mm Hg; p less than 0.01), captopril in combination with OKY-046 induced a decrease both in urinary thromboxane B2 excretion (from 70.8 +/- 12.3 to 54.2 +/- 14.7 pg/min; p less than 0.01) and in mean arterial pressure (from 105.1 +/- 3.8 to 84.2 +/- 3.6 mm Hg; p less than 0.01). Thus, the hypotensive effect of captopril was potentiated by OKY-046. OKY-046 did not affect the changes in plasma renin activity and plasma aldosterone concentration and blunted urinary prostaglandin E2 and 6-keto-prostaglandin F1 alpha excretion in response to captopril. These results indicate that thromboxane A2 counteracts the hypotensive effect of captopril in patients with essential hypertension.

Effect of long-term treatment with diltiazem on atrial natriuretic peptides in spontaneously hypertensive rats

The present study was designed to examine the possible effect of long-term treatment with diltiazem on plasma and atrial concentrations of atrial natriuretic peptides (ANP) in spontaneously hypertensive rats (SHR). Diltiazem treatment reduced blood pressure and ventricular weight in SHR. Plasma ANP concentration in untreated SHR was higher than Wistar-Kyoto rats (WKY). Diltiazem treatment decreased plasma ANP concentration in SHR near to the level of WKY; moreover, plasma ANP concentration was correlated with blood pressure and ventricular weight in treated and untreated SHR. Left atrial ANP concentration in untreated SHR was lower than WKY. Diltiazem treatment increased left atrial ANP concentration in SHR, but this effect was not noted in WKY. These results suggest that the ANP release from the left atrium is chronically stimulated in adult SHR, and that the prevention of an increase in plasma ANP by diltiazem treatment may be, in part, attributed to the improvement of cardiac overload induced by reductions in blood pressure and cardiac hypertrophy.

Selective antagonism of hormone-induced vasoconstriction by synthetic atrial natriuretic factor in the rat microcirculation

Synthetic atrial natriuretic factor (ANF) was either added to suffusate solutions (30 nM) or infused into the jugular vein (0.1 nanomol/min/100 g) of anesthetized rats. Steady-state blood flow was calculated from arteriolar diameter and red blood cell velocity measurements using video microscopy in the intestinal or skeletal muscle microcirculation. Arterioles demonstrated spontaneous vasomotor tone by dilating to topical adenosine, but topical or intravenous ANF did not cause vasodilation. Either angiotensin, norepinephrine, or vasopressin was added to the suffusates in the presence or absence of a cyclooxygenase inhibitor (30 microM, meclofenamate or indomethacin) because each agonist is known to stimulate vasoactive prostanoid synthesis. In the intestine, angiotensin (500 nM) caused 40 +/- 2% blood flow decreases during intravenous saline but only 23 +/- 6% during intravenous ANF. Angiotensin (162 nM) and a cyclooxygenase inhibitor caused 19 +/- 4% blood flow decreases but only 8 +/- 5% decreases with cyclooxygenase inhibitor and topical ANF. In contrast, norepinephrine (2-5 microM) caused vasoconstriction that was not altered by topical or intravenous ANF, either alone or in combination with cyclooxygenase inhibitors. In the spinotrapezius muscle, angiotensin (1-2 nM) plus a cyclooxygenase inhibitor caused 40-60% blood flow decreases but only 20-30% decreases during intravenous or topical ANF. Topical or intravenous ANF did not alter the vasoconstriction evoked by arginine vasopressin (0.5-1.0 nM) or by norepinephrine (40-230 nM). Thus, supraphysiologic concentrations of ANF produced no direct vasodilation in the intestinal or skeletal muscle microcirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding sites for atrial natriuretic factor (ANF) in kidneys and adrenal glands of spontaneously hypertensive (SHR) rats

Binding sites for atrial natriuretic factor (ANF) were studied in kidneys and adrenal glands of 17 week old male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats by quantitative autoradiography using 125I-ANF-28. In kidney, 125I-ANF-28 binding sites were found in high concentrations in glomeruli and in much lower concentrations in the renal papilla. In adrenal gland, 125I-ANF-28 binding sites were highly localized to the zona glomerulosa and were of moderate density in the inner cortical regions. ANF binding sites did not occur in the adrenal medulla. The maximum binding capacity (Bmax) of 125I-ANF-28 was reduced by 50% in the kidney glomeruli of SHRs compared to WKY controls. In contrast, the affinity constant (Ka) for 125I-ANF-28 was elevated by 100% in kidney glomeruli of SHRs. There were no significant strain differences in values for Bmax or Ka for 125I-ANF-28 binding in the adrenal zona glomerulosa. These findings suggest that the natriuretic and diuretic actions of ANF within kidney glomeruli may be compromised in adult SHR rats and these alterations may contribute to the development and maintenance of hypertension in rats of this strain.

The involvement of atriopeptins in blood pressure regulation

The atriopeptins are newly discovered cardiac-derived peptides whose observed actions suggest a role in volume homeostasis and blood pressure regulation. Studies in animal models are underway to pinpoint pathogenetic mechanisms involved in the evolution of hypertension, some of which may well be shared by humans with "essential" hypertension. Preliminary observations indicate that circulating atriopeptin levels are altered in human disease. It is anticipated that exogenously administered atriopeptin may be a helpful pharmacological tool in the management of patients with volume overload and hypertension.

In vivo atrial peptide-venodilation: minimal potency relative to nitroglycerin in dogs

Venodilation is thought to contribute to the hemodynamic actions of atrial peptides. Therefore, we measured the effective vascular compliance (EVC) as a parameter of overall venous tone in 7 pentobarbital anesthetized dogs under autonomic blockade during i.v. infusions of rat atriopeptin II (AP II, up to 100 pmol/kg/min), rat alpha-atrial natriuretic factor, and nitroglycerin (GTN). AP II lowered mean arterial pressure by reducing peripheral vascular resistance with a threshold between 3 and 10 pmol/kg/min (but was ineffective in anesthetized or conscious dogs without autonomic blockade). Neither atrial peptide altered EVC, while GTN augmented EVC and caused a 4.6-fold larger reduction of central venous pressure than AP II at equihypotensive dosage. These findings, with infusion rates probably close to endogeneous release, reveal a vasodilator potency of atrial peptides, which is restricted to systemic arterioles without affecting venous tone.

Binding sites for atrial natriuretic factor (ANF) in brain: alterations in Brattleboro rats

Binding sites for atrial natriuretic factor (ANF-28) were analyzed in discrete brain areas of Brattleboro rats with hereditary diabetes insipidus and Long-Evans (LE) controls by quantitative autoradiography. The maximum binding capacity (Bmax) and affinity constant (Ka) for 125I-ANF-28 were elevated significantly in the subfornical organ of Brattleboro rats compared to matched LE controls. In contrast, values for Bmax and Ka for 125I-ANF-28 binding in choroid plexus and area postrema were similar for rats of the two strains. These findings are consistent with a selective upregulation of ANF-28 binding sites in the subfornical organ of Brattleboro rats which exhibit a profound disturbance in body fluid homeostasis. These alterations in ANF-28 binding sites in the subfornical organ may represent a compensatory response to the absence of vasopressin in the Brattleboro rat.

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 hormones--thirty years after the discovery of atrial volume receptors

Twenty-five years after the discoveries of the existence of atrial granules and of volume receptors in the heart atria the search for natriuretic hormones has led to the isolation and identification of the atrial natriuretic factors (ANF) now considered as a hormonal system. These peptides are probably synthesized and stored in the Golgi apparatus of cardiac myocytes and are released in response to atrial wall stretch following acute plasma volume expansion and increased central blood volume, e.g., during head-out water immersion, in arterial hypertension, or increased left and/or right atrial pressure in cardiac failure, but also possibly in response to increased frequency of myocardial contractions, e.g. in paroxysmal tachycardia. The mechanisms of the renal action of these potent natriuretic hormones are not yet precisely known. Increased GFR may contribute to the initial rise in urinary sodium excretion and increased renal medullary blood flow to the later phase of natriuresis. The proximal tubule, the thin descending and the ascending limb of Henle's loop and especially the medullary collecting tubule were so far incriminated as tubular sites of action of ANF. Finally, recycling of sodium in medullary tissue and secretion of sodium via back-flux from the interstitium into the medullary collecting tubule are postulated to result in the hypernatric urine observed after ANF administration. Direct suppression of the secretion of renin, aldosterone, vasopressin, and vasopressin-stimulated cAMP synthesis may also contribute to its diuretic, natriuretic, and antihypertensive effects. The renal hemodynamic and tubular as well as the adrenal and systemic vascular effects are related to enhanced cGMP synthesis in medium-sized arterial vessels, in glomeruli and specific tubular segments, and in adrenal tissue, and may be calcium dependent. Specific ANF-binding sites were detected in these target organs. Although increased ANF release was observed in response to atrial distension in various disease states, which may contribute to renal sodium elimination in human hypertension and congestive heart failure, further studies are needed to identify its precise physiological and pathophysiological significance.