Glucocorticoid and mineralocorticoid stimulation of atrial natriuretic peptide release in man

Corticosterone treatment results in enhanced release of peptidergic vesicles in astrocytes via cytoskeletal rearrangements

While the effect of stress on neuronal physiology is widely studied, its effect on the functionality of astrocytes is not well understood. We studied the effect of high doses of stress hormone corticosterone, on two physiological properties of astrocytes, i.e., gliotransmission and interastrocytic calcium waves. To study the release of peptidergic vesicles from astrocytes, hippocampal astrocyte cultures were transfected with a plasmid to express pro-atrial natriuretic peptide (ANP) fused with the emerald green fluorescent protein (ANP.emd). The rate of decrease in fluorescence of ANP.emd on application of ionomycin, a calcium ionophore was monitored. Significant increase in the rate of calcium-dependent exocytosis of ANP.emd was observed with the 100 nM and 1 μM corticosterone treatments for 3 h, which depended on the activation of the glucocorticoid receptor. ANP.emd tagged vesicles exhibited increased mobility in astrocyte culture upon corticosterone treatment. Increasing corticosterone concentrations also resulted in concomitant increase in the calcium wave propagation velocity, initiated by focal ATP application. Corticosterone treatment also resulted in increased GFAP expression and F-actin rearrangements. FITC-Phalloidin immunostaining revealed increased formation of cross linked F-actin networks with the 100 nM and 1 μM corticosterone treatment. Alternatively, blockade of actin polymerization and disruption of microtubules prevented the corticosterone-mediated increase in ANP.emd release kinetics. This study reports for the first time the effect of corticosterone on gliotransmission via modulation of cytoskeletal elements. As ANP acts on both neurons and blood vessels, modulation of its release could have functional implications in neurovascular coupling under pathophysiological conditions of stress.

Enhanced Blood Pressure Response to Mineralocorticoid Stimulation in Normotensive Members of Hypertensive Families

Currently normotensive offspring of essential hypertensive parents often have disturbances in blood pressure (BP) regulation such as abnormalities in electrolyte homoeostasis, increased salt-sensitivity and/or impaired renal Na(+)-excretion. Whether an altered reactivity to mineralocorticoids may also play a role is presently unknown. Therefore, we investigated BP (recorded during 24 h), plasma atrial natriuretic factor (ANF), cyclic guanosine monophosphate (cGMP), aldosterone (PA) and renin activity (PRA), 24-h urine electrolyte and cGMP excretions measured on 4 consecutive days, as well as other variables, after 1 week on placebo and after 3 weeks of 9 alpha-fludrocortisone-acetate (9 alpha F) administration, 0.6 mg/d in 12 normotensive sons of essential hypertensive parents (SEH) and 12 body-mass-index- and age-matched (25 +/- 1[+/-SEM]yr) sons of normotensive parents (SN). On placebo, the 2 groups did not differ significantly in average 24 h BP (mean BP 95 +/- 2 vs 95 +/- 2 mmHg), plasma-ANF (40 +/- 7 vs 30 +5 pg/ml), cGMP (6 +/- 0.4 vs 6 +/- 0.5 nmol/l), PRA (1.3 +/- 0.1 vs 1.6 +/- 0.2 ng/ml/h), PA (9 +/- 0.5 vs 10 +/- 0.9 ng/dl), hematocrit (44 +/- 0.7 vs 44 +/- 0.4%) and 96-h urinary-Na+ (mean 205 +/- 13 vs 195 +/- 16 mmol/d), -K+ (69 +/- 6 vs 78 +/- 7 mmol/d) or -cGMP (461 +/- 35 vs 483 +/- 32 nmol/d). 9 alpha F significantly increased BP in SEH (p < 0.005) but not SN (107 +/- 2 vs 100 +/- 2 mmHg, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regional haemodynamic changes during mineralocorticoid hypertension

BACKGROUND

Primary aldosteronism is a cause of hypertension in up to 10% of hypertensive patients, but the mechanisms by which excess aldosterone raises arterial pressure remain unclear.

OBJECTIVE

To investigate the systemic and regional haemodynamic changes during the development and maintenance of aldosterone-induced hypertension and the effect of sympathetic and vasopressin blockade.

METHODS

Responses to intravenous infusion of aldosterone (10 microg/h) for 4 weeks were determined in five conscious sheep. The effects of sympathetic blockade with propranolol and phentolamine or vasopressin V1-receptor blockade with SR59049 were investigated in six further sheep infused with aldosterone.

RESULTS

Aldosterone progressively increased the mean arterial pressure by 20 mmHg over 4 weeks (P < 0.001). The changes in cardiac output were variable between animals, resulting in no overall significant change. Total peripheral conductance was significantly decreased due to selective reductions in mesenteric conductance (from 6.17 +/- 0.27 to 4.46 +/- 0.15 ml/min per mmHg, P < 0.001) and iliac conductance (from 1.54 +/- 0.21 to 1.27 +/- 0.15 ml/min per mmHg, P < 0.001). In contrast, renal and coronary conductance were unchanged and renal blood flow increased from 290 +/- 17 to 350 +/- 28 ml/min (P < 0.01) and coronary blood flow from 34.7 +/- 3.0 to 44.6 +/- 2.5 ml/min (P < 0.05). These aldosterone-induced changes were not inhibited by sympathetic or vasopressin V1-receptor blockade.

CONCLUSION

Excess aldosterone caused a slow progressive increase in arterial pressure, which in the long term depended on reduced total peripheral conductance. This resulted from vasoconstriction in the gut and skeletal muscle, but not the kidney. These effects were not mediated by the sympathetic nervous system or vasopressin.

N-terminal fragments of the proatrial natriuretic peptide in plasma and urine of kidney graft recipients

BACKGROUND

Successful kidney transplantation normalizes elevated proatrial natriuretic peptide (proANP) plasma concentrations of renal failure patients in the early posttransplant period. We evaluated plasma and urinary proANP fragments in the late posttransplant period.

METHODS

Immunoreactive proANP(1-30) and proANP(31-67) were determined in 389 renal transplant (Rtx) recipients in the long-term, follow-up period and in 16 healthy controls.

RESULTS

Rtx recipients had significantly higher concentrations of proANP(1-30) and proANP(31-67) in both plasma and urine than healthy controls. Although their graft function was normal, all of these long-term Rtx recipients were taking glucocorticoids, which increase proANP(1-30) and proANP(31-67) in the circulation to the extent found in this investigation. Two-thirds of these recipients were also taking cyclosporine, which also increases atrial peptides. Urinary proANP(31-67) was significantly higher than urinary proANP(1-30); 5.5-fold in Rtx patients and 2-fold in controls. Deterioration of renal graft function was associated with a rise of plasma proANP(1-30) from 0.98+/-0.66 to 6.28+/-3.55 nmol/l (P<0.0001) and plasma proANP(31-67) from 1.81+/-1.04 to 7.89+/-3.76 nmol/l (P<0.0001). Urinary excretion of proANP(1-30) increased from 0.27+/-0.34 to 5.96+/-5.07 nmol/24 hr (P<0.0001) and proANP(31-67) from 1.45+/-0.85 to 12.23+/-5.12 nmol/24 hr (P<0.0001). Also proteinuria enhanced plasma and urinary proANP fragments.

CONCLUSIONS

ProANP(1-30) and proANP(31-67) of Rtx recipients are affected by immunosuppression, hypertension, renal failure, and proteinuria. One would have expected proANP(1-30) and proANP(31-67) not to normalize because of the glucocorticoids that they were receiving.

Transient pseudo-hypoaldosteronism following resection of the ileum: normal level of lymphocytic aldosterone receptors outside the acute phase

Pseudo-hypoaldosteronism (PHA) is due to mineralocorticoid resistance and manifests as hyponatremia and hyperkalemia with increased plasma aldosterone levels. It may be familial or secondary to abnormal renal sodium handling. We report the case of a 54-year-old woman with multifocal cancer of the colon, who developed PHA after subtotal colectomy, ileal resection and jejunostomy. She was treated with 6 g of salt daily to prevent dehydration, which she stopped herself because of reduced fecal losses. One month later she was admitted with signs of acute adrenal failure, i.e. fatigue, severe nausea, blood pressure of 80/60 mmHg, extracellular dehydration, hyponatremia (118 mmol/l); hyperkalemia (7.6 mmol/l), increased blood urea nitrogen (BUN) (200 mg/dl) and creatininemia (2.5 mg/dl), and decreased plasma bicarbonates level (HCO3-: 16 mmol/l; N: 27-30). However, the plasma cortisol was high (66 microg/100 ml at 10:00 h; N: 8-15) and the ACTH was normal (13 pg/ml, N: 10-60); there was a marked increase in plasma renin activity (>37 ng/ml/h; N supine <3), active renin (869 pg/ml; N supine: 1.120), aldosterone (>2000 pg/ml; N supine <150) and plasma AVP (20 pmol/l; N: 0.5-2.5). The plasma ANH level was 38 pmol/l (N supine: 5-25). A urinary steroidogram resulted in highly elevated tetrahydrocortisol (THF: 13.3 mg/24h; N: 1.4+/-0.8) with no increase in tetrahydrocortisone (THE: 3.16 mg/24h; N: 2.7+/-2.0) excretion, and with low THE/THF (0.24; N: 1.87+/-0.36) and alpha THF/THF (0.35; N: 0.92+/-0.42) ratios. The number of mineralocorticoid receptors in mononuclear leukocytes was in the lower normal range for age, while the number of glucocorticoid receptors was reduced. Small-bowel resection in ileostomized patients causes excessive fecal sodium losses and results in chronic sodium depletion with contraction of the plasma volume and severe secondary hyperaldosteronism. Nevertheless, this hyperaldosteronism may be associated with hyponatremia and hyperkalemia suggesting PHA related to the major importance of the colon for the absorption of sodium. In conclusion, this case report emphasizes 1) the possibility of a syndrome of acquired PHA with severe hyperkalemia after resection of the ileum and colon responding to oral salt supplementation; 2) the major increase in AVP and the small increase in ANH; 3) the strong increase in urinary THF with low THE/THF and alpha THF/THF ratios; 4) the normal number of lymphocytic mineralocorticoid receptors outside the acute episode.

Atrial natriuretic hormone decreases endocrine response to a combined dexamethasone-corticotropin-releasing hormone test

BACKGROUND

An escape from the dexamethasone-induced suppression of pituitary-adrenocortical activity can be provoked by corticotropin-releasing hormone (CRH) in depressed patients, but not in healthy controls. One important antagonist of the CRH-stimulated secretion of corticotropin (ACTH) and cortisol is atrial natriuretic hormone (ANH).

METHODS

To study a potential role of ANH in the dexamethasone-CRH test, we investigated 7 healthy men who did not suppress cortisol below 40 ng/mL after they had received 0.5 mg dexamethasone the evening before.

RESULTS

We found 1) that the CRH-stimulated ACTH and cortisol secretion was significantly reduced by the administration of ANH in comparison to saline; and 2) that there was an increased pituitary-adrenocortical ratio.

CONCLUSIONS

Our results support the view that ANH may also be involved in the frequently observed nonsuppression after dexamethasone during depression. Biol Psychiatry.

Blockade of the renin-angiotensin-aldosterone system prevents growth hormone-induced fluid retention in humans

To test if the renin-angiotensin-aldosterone system (RAAS) is involved in growth hormone (GH)-associated fluid retention, we examined the effect of GH administration in the presence or absence of RAAS blockade at different levels on body fluid homeostasis. Eight subjects were examined in a controlled, randomized double-blinded trial. During four 6-day periods they received subcutaneous GH (6 IU-m-2) or placebo injections and tablets as follows: 1) placebo and placebo, 2) GH and placebo, 3) GH and captopril, and 4) GH and spironolactone. GH increased extracellular volume (liters; placebo 18.87 +/- 0.85; GH + placebo 20.43 +/- 1.01) but this effect was abolished by captopril (GH + captopril 18.82 +/- 0.67) and spironolactone (GH + spironolactone 18.99 +/- 0.85). Correspondingly, the GH-induced reduction in bioimpedance was blocked by captopril and spironolactone. Plasma renin and angiotensin II concentrations increased during all three GH treatment regimens, whereas plasma aldosterone was increased only after GH plus spironolactone. The data demonstrate that GH activates the RAAS and that blockade of the RAAS by two separate mechanisms prevents fluid retention normally encountered after GH exposure. These observations suggest that the RAAS plays a key role in GH-induced regulation of fluid homeostasis.

Atrial natriuretic peptide and feeding activity patterns in rats

This review presents historical data about atrial natriuretic peptide (ANP) from its discovery as an atrial natriuretic factor (ANF) to its role as an atrial natriuretic hormone (ANH). As a hormone, ANP can interact with the hypothalamic-pituitary-adrenal axis (HPA-A) and is related to feeding activity patterns in the rat. Food restriction proved to be an interesting model to investigate this relationship. The role of ANP must be understood within a context of peripheral and central interactions involving different peptides and pathways.

Effect of prednisolone on amino acid-induced changes in renal haemodynamics and tubular function

The effect of oral prednisolone treatment on renal haemodynamics, tubular function and various hormones during amino acid infusion was studied in 14 normal men. A balanced amino acid solution was infused for 120 min, before and after 4 days of prednisolone treatment (40 mg day-1). During amino acid infusion before prednisolone glomerular filtration rate, renal plasma flow, urinary sodium excretion, fractional excretion of sodium, lithium clearance, fractional excretion of lithium, serum insulin (s-insulin), plasma glucagon (p-glucagon) and s-growth hormone increased, whereas p-atrial natriuretic peptide, p-aldosterone, p-vasopressin and s-insulin-like growth factor 1 were unchanged, and potassium excretion and fractional excretion of potassium fell. After prednisolone treatment the most important differences during amino acid infusion were a significantly lower fractional excretion of sodium after 120 min (before prednisolone 26%; after prednisolone-7%; p < 0.05), a more pronounced increase in s-insulin after 120 min (before 118%; after 200%; p < 0.05) and a lower s-potassium. In conclusion, amino acid infusion increased fractional sodium excretion in healthy men, and this increase was reduced by prednisolone due to increased reabsorption in the distal tubules. It is suggested that the more pronounced the increases in plasma insulin and the decrease in serum potassium are mediators of the increased distal tubular sodium reabsorption during amino acid infusion during prednisolone treatment.

Reduced plasma cyclic GMP but normal renal responses to atrial natriuretic factor in pre-hypertension

The amount of, and response of the kidneys to, endogenous natriuretic factor(s) could be important in the pathogenesis of essential hypertension. Searching for possible disturbance(s) related to atrial natriuretic factor (ANF) and its second messenger, cyclic guanosine monophosphate (c-GMP), we assessed plasma immunoreactive (ir) ANF and c-GMP, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), urinary c-GMP, absolute and fractional (FE) excretions of sodium (Na) and chloride (Cl) before and during infusions of low ANF doses or vehicle (V) in 7 normotensive sons of essential hypertensive parents (SEH) compared with 7 sons of normotensive parents (SN). Each subject was infused at 2-week intervals in a single-blind randomized sequence with 4 different solutions: V only or ANF 0.004, 0.008 and 0.016 microgram/kg/min, infused over 90 min. Plasma irANF was lower in SEH than in SN (p < 0.001) during vehicle infusion. Basal plasma c-GMP levels were, on all 4 different study days lower (p < 0.05 to < 0.01) in SEH in SN. Response of plasma c-GMP to infused ANF was also slightly decreased in SEH (p < 0.05 to < 0.01). BP, ERPF and GFR did not differ between SEH and SN and were unchanged during the 4 infusions. Urinary c-GMP excretion, FENa and FECl increased dose-dependently during ANF (p < 0.05 to < 0.0001) but not V infusions. These findings indicate that at the stage of pre-hypertension a disturbance in the ANF-c-GMP regulatory pathway may occur, which is expressed primarily at the circulatory rather than the renal excretory level.

Circadian blood pressure rhythm and atrial natriuretic peptide in prednisolone-induced blood pressure elevation

The effect of prednisolone, given as a 4-day oral treatment, on 24-h ambulatory blood pressure rhythm, vasoactive hormones and correlation between blood pressure and vasoactive hormones were studied in 11 healthy men. Blood pressure was monitored at intervals of 15 min during the day and of 30 min during the night. Plasma concentrations of angiotensin II, aldosterone, atrial natriuretic peptide (ANP) and arginine vasopressin and serum concentration of insulin were measured in the morning during basal conditions. The 24-h systolic, diastolic and mean blood pressures were significantly higher after prednisolone treatment. Waking blood pressure was not significantly changed, but sleeping systolic and mean blood pressures were significantly elevated after treatment. The nocturnal systolic blood pressure fall was less pronounced after treatment (before 22%, and after 16%, p<0.01), whereas the nocturnal, mean and diastolic dips were preserved. ANP was significantly increased by prednisolone treatment, from 10.1 to 14.6 pmol l-1, p<0.005. The changes in concentration of ANP were significantly correlated to the changes in 24-h diastolic blood pressure (r = -0.63, p<0.05), 24-h mean blood pressure (r = -0.68, p<0.05), waking diastolic blood pressure (r = 0.83, p<0.01) and waking mean blood pressure (r = -0.67, p<0.01). We found that short-term prednisolone treatment elevated the overall 24-h blood pressure, reduced systolic blood pressure fall during sleep, and increased plasma concentration of ANP, and that the increase in ANP was inversely correlated to the increase in blood pressure. We suggest that the increase in ANP is a secondary and compensatory phenomenon which at least to some extent counteracts the hypertensive and sodium retaining effect of prednisolone.

Glucocorticoid-induced sympathoinhibition in humans

OBJECTIVE

To test whether glucocorticoids inhibit sympathetic nerve activity or norepinephrine release in humans, as has been suggested by results in laboratory animals.

METHODS

This was a double-blind, placebo-controlled, randomized crossover study performed at the Clinical Center of the National Institutes of Health. Thirteen normal volunteers received 20 mg prednisone or placebo orally each morning for 1 week, followed by a washout period of 1 week and then by treatment with the other drug for 1 week. On the last day of each treatment week, blood samples were drawn for measurements of plasma levels of catecholamines and their metabolites, of cortisol, and of corticotropin at baseline and during reflexive sympathetic stimulation elicited by lower body negative pressure (-15 mm Hg). A 24-hour urine collection was obtained at the end of each week of treatment for measurement of urinary excretion of catechols. In eight subjects, directly recorded peroneal skeletal muscle sympathetic nerve activity was also measured after both treatments.

RESULTS

Prednisone significantly decreased sympathetic nerve activity by 23% +/- 6%, plasma norepinephrine levels by 27% +/- 6%, and plasma corticotropin levels by 77%. Blood pressure, heart rate, body weight, and urinary excretion of catechols and electrolytes were unaffected. Prednisone did not alter proportionate increments in sympathetic nerve activity or plasma norepinephrine levels during lower body negative pressure. Relationships between sympathetic nerve activity and plasma norepinephrine levels were unchanged.

CONCLUSIONS

Glucocorticoids decrease sympathoneural outflows in humans without affecting acute sympathoneural responses to decreased cardiac filling and probably without affecting presynaptic modulation of norepinephrine release.

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.

Fludrocortisone induced heart failure in Addison's disease

The first reported case of congestive cardiac failure in a child with Addison's disease secondary to fludrocortisone therapy is presented. A renal adaptation to compensate for chronic salt and water deprivation is suggested as a possible mechanism for the development of congestive cardiac failure in this patient.

Atrial natriuretic factor: does it have a role in psychiatry?

Atrial natriuretic factor (ANF) is the first of a group of atrial natriuretic peptides (ANPs) discovered since 1981. This group of peptides is thought to have an important role in sodium homeostasis and regulation of fluid volume. Although the role of ANF in cardiovascular and renal disorders is under investigation, the specific signaling involvement that ANF may have in the central nervous system is still unexplored. To date, ANF has not as yet been associated with a given functional area in the brain, nor has it been shown to be linked to any particular psychopathology. Neuropharmacology research of these peptides and their drug manipulation is needed to advance our knowledge of the possible role of ANF in psychiatry beyond the current level of speculation.

Effects of fludrocortisone on sympathetic nerve activity in humans

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty-four-hour pattern of atrial natriuretic peptide in heart transplantation: evidence for lack of circadian rhythm. Temporal inter-relationships with plasma renin activity, aldosterone and cortisol

We have investigated the circadian rhythm of plasma atrial natriuretic peptide in 13 stable output heart transplanted patients, all without evidence of histological rejection and cardiac impairment, following antirejection therapy with Cyclosporine, Azathioprine and Prednisone. The 24-h pattern of plasma renin activity, plasma aldosterone and plasma cortisol has been studied as well. All the investigated variables were assayed six times over the 24-h span. The circadian time-qualified data were analyzed by ANOVA and Cosinor method. The 24-h mean levels of atrial natriuretic peptide, plasma renin activity and plasma aldosterone are significantly increased, while the concentrations of plasma cortisol are reduced in the heart transplanted recipients. ANOVA detected a significant within-day variability of all these humoral variables only in healthy subjects. A statistically significant circadian rhythm was validated by Cosinor procedure for all the investigated molecules in healthy subjects but not in heart transplanted patients. In our opinion, the increase of atrial natriuretic peptide is a counterregulatory mechanism aimed to compensate the cyclosporine-mediated activation of the renin-angiotensin-aldosterone system. The disappearance of the plasma renin activity, aldosterone and atrial natriuretic peptide circadian rhythm can be ascribed to the constant activation of the renin-angiotensin-aldosterone system. The hypocortisolism is due, in our opinion, both to glucocorticoid therapy and increase of plasma ANP concentration.

Atrial natriuretic peptide and arginine vasopressin secretion in schizophrenic patients

Plasma levels of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were measured in 15 patients with schizophrenic or schizoaffective disorders and 15 healthy volunteers during oral water loading at 20 ml/kg. In the patient group, plasma AVP was secreted even when plasma osmolality was below 270 mosmol/kg, although the sensitivity of AVP secretion response to osmolality was lower than in the controls. The ANP level was higher in the group of patients than in the controls. There was a negative correlation between plasma ANP and osmolality in the patients. We speculate that the volume expansion caused by inappropriate AVP secretion stimulated plasma ANP release and that the natriuresis resulting from the elevated plasma ANP level might contribute to hyponatremia.

Circadian variations of plasma atrial natriuretic peptide and corticosterone in rats with continuous or restricted access to food

In the present study plasma Atrial Natriuretic Peptide (ANP) and Corticosterone (B) levels were determined in 2 groups of Wistar rats, a Control group (C) with free access to food, and a Food Shift group (FS) with access to food only from 0900 to 1100 h for 2 weeks. Blood samples were collected by decapitation at 4 hour intervals. ANOVA indicated that B varied over time in both groups (F (6.46) = 10.14, p < 0.0001 for C and F (6.5) = 5.10, p = 0.0005 for FS). There was also time variation in plasma ANP levels in both groups (F (6.54) = 3.78, p = 0.003 for C and F (6.48) = 2.73, p = 0.02 for FS group). Plasma B presented circadian variations from 78 +/- 17 nmol/l (mean +/- SEM) at 0800 h to 339 +/- 79 nmol/l at 2000 h. The day peak plasma ANP level (pmol/l) was also attained at 2000 h (68 +/- 19). This value was higher than all others measured throughout the day. The restricted feeding regimen resulted in a 12 hour shift of peak B values (395 +/- 39 vs 125 +/- 24). The FS rats presented the highest ANP level at 0800 h. The present study indicates similar circadian variations of plasma ANP and B in rats on an ad lib or restricted feeding regimen. ANP and B secretion may occur in anticipation of the feeding period or day activity.

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

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

Adrenalectomy and dexamethasone administration: effect on atrial natriuretic peptide synthesis and circulating forms

Previous in vivo and in vitro studies have reported a variety of glucocorticoid effects on the synthesis and secretion of immunoreactive atrial natriuretic peptide (ir-ANP) into plasma. To further define glucocorticoid modulation of ir-ANP, we have measured ir-ANP levels in plasma and the four cardiac chambers, and tissue ANP mRNA levels, in intact rats and adrenalectomized rats with or without dexamethasone treatment for 1, 2, 4, 8 and 16 days. Plasma levels fell by 50% between 8 and 16 days post-adrenalectomy; in contrast, dexamethasone treatment caused a 3-fold rise in plasma ANP 1-2 days post-adrenalectomy, with levels gradually returning to control by day 16. Circulating forms of ANP were unchanged by adrenalectomy or dexamethasone treatment, as were atrial ANP concentrations and ANP mRNA levels. Left ventricular ANP concentrations rose with dexamethasone treatment, and ventricular ANP mRNA levels changed in parallel with those of circulating ANP. The in vivo effect of glucocorticoids (at moderate rather than very high doses) on ANP synthesis and secretion thus appears to be predominantly but not exclusively upon the left ventricle rather than the atria.

Distribution of atrial natriuretic peptide in the conduction system and ventricular muscles of the human heart

Atrial natriuretic peptide (ANP), a cardiac hormone, is known to be located in the atrial specific granules, but its presence and localization in the ventricular muscle of the human heart has not been examined fully. Using a specific antibody to human ANP, we studied the conduction system and ventricular muscle with immunohistochemical and ultrastructural methods in 30 hearts obtained at autopsy. These included 12 normal and 18 diseased hearts. In the normal hearts, ANP-positive granules, which were regularly observed in the atrial myocytes, were found in small quantities in the cells of the penetrating and branching bundles in 4 of 12, and in the cells of the ventricular free walls in 2 of the 12 hearts. In the diseased hearts, the positivity increased significantly (P less than 0.05), being found in 13 of 18 (72.2%) conduction systems and 10 of 18 (55.6%) ventricular muscles. The granules were confirmed to be immunoreactive with ANP by ultrastructural examination. Furthermore, the presence of ANP mRNA in the conduction system as well as in the ventricular myocytes was demonstrated by Northern blot hybridization for which we used the complementary DNA of human ANP. Thus, a small quantity of ANP appears to be synthesized and stored in the conduction system and ventricles of some normal hearts. However, ANP was shown to be present in a larger percentage of the diseased hearts.

Mannitol stimulates atrial natriuretic peptide release in humans

The purpose of this study was to determine if mannitol stimulates atrial natriuretic peptide (ANP) release in humans and to examine potential mechanisms for this effect. Twenty patients requiring cardiac catheterization were randomized to receive either mannitol (15-g bolus followed by 15% infusion mixed in 75 mmol/L saline at 100 mL/h for 1 hour) or an equal volume of 75 mmol/L saline, intravenously (IV). All measurements were made at three time points: at baseline, at 10 minutes (after the bolus but before radiocontrast administration), and at 60 minutes (after completion of the study). Baseline plasma ANP (PANP) measurements (mean +/- SE) were similar in both groups (saline, 73 +/- 38 pg/mL; mannitol, 62 +/- 11 pg/mL). PANP increased significantly over time for the set of all patients (analysis of variance [ANOVA], P less than 0.05); however, at 10 minutes PANP increased significantly only in the group receiving mannitol (saline, 76 +/- 43 pg/mL; mannitol, 100 +/- 29 pg/mL) (P less than 0.04). Serum osmolality (SOSM), over time for the set of all patients (ANOVA, P less than 0.04). At 10 minutes there were significant increases only in the group receiving mannitol, and after radiocontrast, there were significant increases in both groups for all parameters. Regression analysis demonstrated a significant correlation between the change in PANP and the change in SOSM (P less than 0.04, r = 0.33). In conclusion, intravascular infusion of mannitol or radiocontrast increased PANP levels. The mechanism may be multifactorial, with a potential role for an increase in SOSM and/or PADH.

Atrial natriuretic peptide in Cushing's disease

Atrial Natriuretic Peptide (ANF), is secreted by atrial myocytes in response to atrial stretch. Its plasma levels have been found elevated in conditions leading to salt and fluid repletion and consequent atrial distention. Recently, it has been demonstrated that dexamethasone can enhance ANF secretion, by acting on ANF gene expression and mRNA synthesis. High plasma levels of ANF have been observed in normal man after administration of cortisol and ACTH. In the case of glucocorticoid excess, as in Cushing's disease, limited and conflicting data are available. Therefore, we measured ANF basal values and ANF response to postural changes and volume expansion in eight patients with Cushing's disease. In our patients ANF values were higher than normals. ANF responded to volume expansion, 47.8 +/- 5.1 pg/ml before sodium load and 69.9 +/- 7.0 pg/ml after sodium load, and changed minimally after postural manoeuvres, 47.3 +/- 3.2 pg/ml supine and 41.7 +/- 5.1 pg/ml upright. These data indicate that ANF secretion is enhanced in Cushing's disease, and its regulation is partially altered. Since in this condition hypervolemia has not been certainly demonstrated, a direct relationship between elevated ANF and glucocorticoid excess could be suggested.

Atrial natriuretic factor and autonomic nervous system function in man

To delineate a possible interaction of atrial natriuretic peptide ANF-(99-126) with autonomic nervous system function in humans, a spectrum of indices were assessed in 10 healthy young men during a 90 min iv administration of a) synthetic ANF-(99-126) 50 micrograms bolus followed by 0.025 micrograms.kg-1.min-1, b) the potent vasodilator sodium nitroprusside (SNP) 0.35 micrograms.kg-1. min-1, or c) vehicle 0.9% NaCl40 ml and 20% albumin 5 ml, in random sequence. Plasma immunoreactive ANF (irANF) rose from 32 to 1700 pg.ml-1 during the ANF-(99-126) infusion and was stable during SNP or vehicle. Infusion of ANF-(99-126) and SNP, but not vehicle, decreased diastolic blood pressure (BP) on average by -9 and -7.5%, respectively; systolic BP was largely unchanged. Heart rate (HR, + 15 and 12%) or plasma norepinephrine (NE) rose similarly during ANF-(99-126) and SNP infusions, and the systolic BP response to orthostasis was similar (-18 mmHg). The following autonomic indices did not differ significantly after the 3 infusions: responses of HR and NE to orthrostasis; reflex bradycardic response to phenylephrine (PE)-induced rise in systolic BP (+ 20 mmHg); responses of BP to hyperventilation, PE, or 3 min of sustained handgrip; and beat-to-beat variation (R-R interval) during deep breathing. The immediate orthostatic HR response (30/15 R-R interval ratio) fell similarly during infusion of ANF-(99-126) or nitroprusside. The findings indicate that in healthy men the function of the autonomic nervous system is not notably impaired by high circulating ANF levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Interrelationship between cortisol and atrial natriuretic factor in the immature ovine fetus

1. In chronically cannulated ovine fetuses (100-130 days of gestation) the infusion of cortisol (86.7 +/- 15 micrograms/h for 4 h) or human atrial natriuretic factor (ANF; 4.4 micrograms for 2 h) resulted in highly significant increases in the excretion of sodium, chloride, potassium and water. 2. Cortisol had no significant effect on fetal plasma ANF concentrations. All values are mean and s.e.m. Plasma immunoreactive ANF was 53 +/- 5 and 67.3 +/- 13 pmol/L in the 4 h saline infused fetuses, and 51.3 +/- 14.3 and 74 +/- 13.3 pmol/L in cortisol-infused fetuses (n = 7). A separate group of fetuses received 2 h infusions of saline or hANF (4.4 micrograms/h), and plasma IR-ANF values were measured (n = 3). The values, at 0, 60, 90 and 120 min were, respectively, 19.7 +/- 3, 17.3 +/- 0.7, 18.7 +/- 3.7 and 20.7 +/- 3.7 pmol/L in the saline infused group, and 25.3 +/- 5.3, 80.7 +/- 32.3, 123.3 +/- 4.3 and 100 +/- 15 pmol/L in the ANF-infused fetuses. 3. Blood cortisol concentrations, in fetuses infused for 4 h with 0.9% NaCl, were 3.1 +/- 0.8 nmol/L (n = 7); in fetuses infused with 0.9% NaCl for 2 h were 3.6 +/- 1 nmol/L (n = 3); in fetuses infused for 4 h with cortisol were 19.9 +/- 1.9 nmol/L (n = 7); and in fetuses infused with hANF for 2 h were 6.0 +/- 3.0 nmol/L (n = 5). 4. There was no effect of fetal hANF infusion on maternal or fetal blood aldosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide: water and electrolyte homeostasis

In the few years since its identification, a clear role for ANP in the regulation of water and electrolyte balance has emerged (Figure 3). The peptide is released in response to blood volume expansion, both acutely and gradually during changes in dietary sodium intake. Similarly, plasma levels are elevated in pathophysiological conditions such as cardiac and renal failure. It has become apparent that ANP has natriuretic, diuretic and vasorelaxant properties. Many of the original studies employed what we now know to be pharmacological doses of the peptide. However, recent reports have confirmed that small, sustained elevations in plasma ANP within or marginally above the 'normal' physiological range produce similar effects. A number of recent studies have tried to specifically address the physiological relevance of ANP. Although undoubtedly release by atrial distension and effective when infused to similar concentrations, atrial distension also has other effects via neural pathways. Thus, the demonstration that excretion of saline is impaired by atrial appendectomy (Benjamin et al, 1988) does not imply that this is only due to the absence of an atrial hormone. Goetz et al (1986) demonstrated that in the denervated heart, although ANP is still released, the excretion of a saline load is impaired. Similarly, in man, Richards et al (1988a) needed to infuse ANP to much higher plasma levels than those achieved by a saline load in order to reproduce the natriuresis. Although these experiments can be criticized, they confirm that ANP is not the sole mechanism for excreting a volume load, or for the natriuresis following atrial distension, but that these effects are likely to reflect the balance between ANP, AVP, the renin-angiotensin and autonomic nervous systems. In rats immunized against ANP (Greenwald et al, 1988), although the ability to excrete an acute saline load was impaired, long-term sodium balance was normal, suggesting that the rats were able to compensate for the absence of ANP. Many of the actions of ANP can be explained by antagonism of the renin-angiotensin-aldosterone system. Teleologically, it seems appropriate that a natriuretic hormone should counterbalance the major pressor and antinatriuretic hormones within the body. There is good evidence for cellular interactions between angiotensin, AVP, aldosterone and ANP at a number of discrete sites which are additional to the straightforward physiological antagonism of systems with opposing actions. ANP inhibits aldosterone secretion directly and may also reduce renal renin release. In the vascular tree there is evidence that ANP specifically blocks the vasoconstrictor actions of angiotensin II and possibly AVP.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial natriuretic peptide in man

The heart is the major source of atrial natriuretic peptides (ANP). A propeptide is stored in atrial myocytes. In normal humans, atrial distension secondary to volume overload and/or increased atrial pressures are thought to stimulate the secretion of biologically active alpha-ANP (ANF-[99-126], 28 amino residues) into the circulation. Plasma immunoreactive ANP (irANP) rises in response to acute sodium-volume loading, the central shift of volume produced by lying down or by immersion, acute increases in blood pressure (BP), dynamic exercise, or the administration of glucocorticoids or mineralocorticoids. Plasma irANP also rises with aging. Synthetic alpha-ANP infused acutely i.v. can lower BP, reduce plasma volume by an extravascular shift, cause baroreflex-mediated sympathetic activation, directly inhibit adrenal steroidogenesis and lower plasma aldosterone and cortisol, directly inhibit renal renin release, elevate plasma insulin; diuresis, free water clearance and natriuresis increase already in response to low alpha-ANP doses that raise plasma irANP within the physiological-pathological range. It follows that in addition to direct influences on cardiovascular and renal function, the ANP system may comprise a cardio-adrenal feedback mechanism and perhaps also modulate insulin and the release of ADH. The major although yet unproven physiological role of the ANP system may be the protection of the heart against volume and/or pressure overload. The pathophysiological, diagnostic and therapeutic aspects of elevated plasma irANP values, ANP measurements, or administration of synthetic ANP, respectively, in various diseases are currently under intense study and of great potential interest.