Dopaminergic modulation of 18-hydroxycorticosterone secretion in man

Comparative Effects of Dopaminergic Agonists on Cardiovascular, Renal, and Renin-Angiotensin Systems in Hypertensive Patients

The role of dopaminergic receptors on renal function has been extensively studied. Recently dopaminergic receptor has been classified in two subtypes D1 and D2, which seem to have different modulatory function. However, the role of dopaminergic receptors on cardiovascular function and more specifically the potential role of dopaminergic agonists as antihypertensive agents has not yet been clarified. Nine outpatients with mild and moderate hypertension were studied in the Cardiology Service of Vargas Hospital with a D1 agonist, piribedil, at 50-100 mg/day, orally, for 8 weeks, and with a D2 agonist, bromocriptine, at 2.5 - 5 mg/day, orally, for an another 8 weeks by using a placebo comparative crossover design. Piribedil reduced blood pressure with a modest increase in heart rate, plasma renin activity, and of plasma aldosterone, and an important increment of renal function. Bromocriptine reduced blood pressure with a decrease in heart rate and plasma aldosterone without altering renal function. There was no orthostatic hypotension with either agent. The authors conclude that activation of dopaminergic D1 receptor induces a vasodilatory and antihypertensive effect with a reflex increase in sympathetic tone, whereas activation of dopaminergic D2 receptor induces a decrease in sympathetic tone, probably due to a decrease in norepinephrine release at adrenergic endings. The potential effect of these compounds as antihypertensive agents is of great interest because blood pressure reduction can be induced by a new mechanism, i.e. activation of dopaminergic receptors which results in a decrease of the renin angiotensin system or a vasodilatory action.(ABSTRACT TRUNCATED AT 250 WORDS)

The neuroendocrinological profile of roxindole, a dopamine autoreceptor agonist, in schizophrenic patients

Roxindole is a potent autoreceptor-selective dopamine agonist with additional properties as a serotonin reuptake inhibitor and 5-HT1A agonist. In order to get more insight into its mode of action in various psychiatric populations, we evaluated the effects of subchronic roxindole treatment on pituitary and adrenal hormone secretion, i.e. release of prolactin, thyroid stimulating hormone (TSH), growth hormone (GH), luteinizing hormone (LH), and cortisol. Fifteen schizophrenic patients with positive and negative symptomatology, respectively, were treated with roxindole for 28 days. Both basal and thyrotropin releasing hormone (TRH) -induced prolactin secretion diminished significantly to 26.4% and 22.8% of baseline levels, respectively, under roxindole. Basal GH secretion was insignificantly elevated by 89%, whereas GH levels increased nearly 3-fold after stimulation by TRH. TSH levels decreased insignificantly to 57.5% of baseline levels, while TRH-induced TSH release was not affected by subchronic roxindole. Roxindole treatment influenced neither LH secretion nor cortisol release. Our results indicate that roxindole's dopaminergic actions might prevail over its serotonergic effects, at least as far as the regulation of anterior pituitary hormone secretion is concerned.

Investigation of the salivary 18-hydroxycorticosterone:aldosterone ratio in man using a direct assay

A method for the direct determination of 18-hydroxycorticosterone (18OHB) in human saliva has been developed and validated. Saliva was collected at 30 min and 1 h intervals between 0600 and 2200 h from healthy men and women for the determination of 18OHB (SHB), aldosterone (SA) and glucocorticoids (SGC = cortisol + cortisone). SHB was highly correlated with SA (r = 0.75; P less than 0.001) but even more highly with SGC (r = 0.89; P greater than 0.001). Multiple regression analysis confirmed that SGC was a more important determinant of SHB than was SA. Though the concentrations of 18OHB and aldosterone were highly correlated there was considerable variation in the 18OHB:aldosterone ratio during the period of saliva collection. This ratio tended to be highest in the morning and lowest in the evening and was weakly correlated with SGC level (r = 0.62; P less than 0.01). The 18OHB:aldosterone ratio in saliva approximates to, and is highly correlated with, that in plasma. We suggest that the fluctuations in SHB:SA ratio correspond to the relative rates of secretion of 18OHB and aldosterone and that this ratio is modulated either by ACTH or by cortisol. Whether this indicates that 18OHB is a by-product of glucocorticoid as well as aldosterone metabolism, or whether this implies a separate physiological role for the steroid remains to be clarified.

Central dopaminergic regulation of aldosterone secretion in sheep

Central dopaminergic mechanisms involved in the regulation of plasma aldosterone concentration were investigated in 16 conscious sheep following Na depletion with intramuscularly administered furosemide. Intracerebroventricular infusion of dopamine (20 micrograms/min) decreased plasma aldosterone significantly to 52 +/- 8% of basal level and increased plasma renin activity (PRA) significantly to 172 +/- 25% of basal level in this animal model. In addition, intracerebroventricular infusion of the dopamine antagonist metoclopramide (20 micrograms/min) in artificial cerebrospinal fluid vehicle significantly increased aldosterone levels to 144 +/- 14% of basal level and decreased PRA to 62 +/- 5% of basal value. Neither intracerebroventricular infusion of the vehicle nor intravenous infusions of metoclopramide or dopamine at the same doses changed aldosterone or PRA levels. Intracerebroventricular bolus injections of metoclopramide (20 micrograms/kg in 0.4 ml of vehicle) were also effective, increasing aldosterone levels to 266 +/- 22% of basal level and decreasing PRA to 70 +/- 12% of basal level. Intravenous bolus injections of the same dose of metoclopramide were ineffective. Dopamine was infused intracerebroventricularly into two uniadrenalectomized sheep with the remaining adrenal transplanted to the neck. Aldosterone levels were decreased to 49 +/- 10% of basal level, and PRA was increased to 157 +/- 10% of basal value. None of the infusions or injections changed arterial or intracranial pressure, or plasma K, Na, and cortisol levels. These data indicate that endogenous or exogenous dopamine may act on central dopamine receptors to decrease plasma aldosterone concentration by an unknown humoral mechanism. The known aldosterone regulators, plasma Na, K, angiotensin II, and adrenocorticotropic hormone, are not involved in the regulation.

Effects of dopaminergic drugs on plasma levels of steroid hormones in conscious dogs

Progesterone, cortisol and testosterone levels were measured by radioimmunoassay in peripheral venous blood of conscious dogs. I.v. injections of the dopamine receptor agonists apomorphine (0.05 mg/kg) and bromocriptine (0.1 mg/kg) increased progesterone levels (and cortisol levels, as previously shown) in dogs of both sexes. The response to apomorphine was abolished by pretreatments with peripheral dopamine receptor antagonists (domperidone and halopemide). Progesterone and cortisol responses to the dopamine receptor agonists were parallel, but the ratio of concentration was 1/100. Testosterone levels were not modified. These results suggest that the dopamine receptor agonists stimulate progesterone release from the adrenal glands at a site functionally accessible to the peripheral dopamine receptor antagonists. In addition, the neuroleptic haloperidol (0.1 mg/kg) was shown to cause long lasting increases of progesterone levels.

Dopamine selectively inhibits aldosterone responses to angiotensin II in humans

Previous studies have suggested that dopamine may have an important role as an inhibitor of aldosterone secretion in humans. Recent studies have also suggested that the adrenergic nervous system may have an important role in controlling aldosterone secretion. The present study investigated the effects of dopamine on aldosterone secretion in response to angiotensin II, with and without pretreatment with propranolol, and to adrenocorticotropic hormone, another known stimulator of aldosterone secretion. Nine normal subjects in balance at 10 mEq sodium intake received dopamine (4 micrograms/kg/min) or vehicle for 270 minutes on 2 consecutive days on three separate occasions. After 120 minutes of dopamine infusion, the subjects received a 30-minute intravenous infusion of angiotensin II (in cumulative doses of 0.5, 1, 2, 4, and 6 pmol/kg/min), angiotensin II after oral pretreatment with propranolol, or adrenocorticotropic hormone (in cumulative doses of 0.5, 1, 2, and 5 U/hr). Aldosterone responses to 2, 4, and 6 pmol/kg/min of angiotensin II (without propranolol) were greater in vehicle-treated than in dopamine-treated subjects (p less than 0.05), as was the slope of the angiotensin II-vehicle dose-response curve (0.46, p less than 0.05). Propranolol suppressed the aldosterone response to angiotensin II, but dopamine still inhibited the response. Aldosterone and cortisol secretion were stimulated equally by adrenocorticotropic hormone in dopamine-treated and vehicle-treated groups. These results suggest that dopamine selectively inhibits the aldosterone response to angiotensin II and that this response is not mediated by teh activity of dopamine at beta-adrenergic receptors.

Role of dopamine in the regulation of aldosterone and 18-hydroxycorticosterone secretion in man

This study was designed to investigate dopaminergic mechanisms involved in the control of corticosteroid secretion. Administration of the dopamine agonist bromocriptine (2.5 mg three times a day for 4 days) to 10 normal males suppressed (p less than 0.01) plasma 18-hydroxycorticosterone (18-OHB) responses to upright posture, isometric handgrip exercise, furosemide administration and angiotensin II infusion without altering supine blood pressure, electrolytes or plasma cortisol. Plasma 18-OHB responses to adrenocorticotropic hormone infusion were not altered by bromocriptine treatment. These observations suggest that angiotensin-mediated 18-OHB and aldosterone secretion is selectively inhibited by dopaminergic mechanisms. Thus, dopamine and angiotensin II may operate as opposing factors in the control of aldosterone biosynthesis.

Dopaminergic suppression of angiotensin II-induced aldosterone secretion in man: differential responses during sodium loading and depletion

Previous studies have shown that aldosterone secretion may be inhibited by dopaminergic mechanisms in man. Dopamine does not inhibit aldosterone responses to angiotensin II in sodium-replete normal subjects. Since sodium deficiency is associated with a reduction in renal dopamine formation, we investigated the effect of dopamine on angiotensin II-induced aldosterone secretion in the sodium-depleted state. Six normal subjects in balance at 10 mEq sodium intake (UNaV 17 +/- 2 meq/24 hr) received dopamine 4 micrograms/kg/min or vehicle for 210 minutes on two consecutive days. After 60 minutes of the dopamine or vehicle infusion, the subjects received successive 30-minute infusions of angiotensin II in increasing doses of 0.5, 1, 2, 4 and 6 picomol/kg/min. Control plasma aldosterone concentrations before vehicle or dopamine were 15 +/- 3 (mean 1 +/- SE) and 25 +/- 3 ng/dL, respectively. Aldosterone responses to angiotensin II were greater with vehicle than dopamine at angiotensin II doses of 4 and 6 picomol/kg/min (P less than 0.025). The slope of angiotensin-aldosterone dose-response curve was steeper with vehicle (0.33) than with dopamine (0.16), P less than 0.01. Serum prolactin concentrations were lower with dopamine (1.6 +/- 0.8 ng/mL) than with vehicle (6.4 +/- 1.2 ng/mL, P less than 0.05) by 120 minutes of infusion and remained suppressed with dopamine for the remainder of the dopamine infusion. Diastolic blood pressure was higher (P less than 0.05) with vehicle than with dopamine at angiotensin II doses of 2, 4, and 6 picomol/kg/min. Dopamine administration was associated with an increase in plasma cortisol concentration from 90 to 150 minutes of infusion (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian variation in plasma dopamine levels in man

Nocturnal and daytime recumbent secretory patterns of norepinephrine, epinephrine and dopamine were determined at 30 min intervals in 9 normotensive males. Plasma levels of dopamine as well as those of norepinephrine and epinephrine followed a circadian pattern in these recumbent males. Plasma levels of dopamine were more closely related to clock time (r = -0.54, p less than 0.001) than either norepinephrine or epinephrine levels. As for norepinephrine and epinephrine, the sleep period in all 9 males was characterized by a paucity of dopamine secretory peaks as well as lower mean dopamine levels than during the awake state. There was a strong relationship between the circadian changes in plasma dopamine levels and those of norepinephrine (r = 0.92) and epinephrine (r = 0.78) throughout the 24-h period of recumbency. These interrelationships are consistent with a common regulatory mechanism governing the sleep/wake and/or rest/activity in plasma catecholamine levels.

Evidence for direct inhibitory effects of dopamine on zona glomerulosa secretion of 18-hydroxycorticosterone in rhesus monkeys

This study was designed to more selectively investigate the dopaminergic regulation of 18-hydroxycorticosterone (18-OHB) and aldosterone production by the adrenal zona glomerulosa. Mature rhesus monkeys received either an infusion of dopamine (2 micrograms/kg/min) or 5% dextrose (0.2 ml/min) over a 60 min period (N=6). Dopamine had no effect on plasma levels of renin activity, cortisol, corticosterone, aldosterone or blood pressure. However, dopamine suppressed (p less than 0.05) plasma 18-OHB levels from a baseline of 31.6 +/- 3.5 ng/dl to 23.6 +/- 2.1 ng/dl at 60 min after onset of infusion. This observation is in agreement with some studies in humans but differs from others in which no depression in 18-OHB was observed following dopamine infusion. Dopamine infusion markedly (p less than 0.001) suppressed plasma PRL levels by 30 min after onset of infusion. Corticosteroid responses to metoclopramide (200 micrograms/kg) after dexamethasone 1 mg im every 6 h X 5 days or placebo treatment (vehicle im every 6 h X 5 days) was then evaluated. Dexamethasone significantly suppressed basal cortisol, corticosterone, 18-OHB and aldosterone. Although dexamethasone blunted the prolactin response, it did not inhibit the aldosterone response to metoclopramide. The 18-OHB response to metoclopramide was increased (p less than 0.01) following dexamethasone treatment. Following dexamethasone suppression, 18-OHB levels were still lowered (p less than 0.05) by dopamine infusion. These results suggest that dopamine selectively inhibits zona glomerulosa production of 18-OHB and aldosterone in rhesus monkeys.

Glucocorticoid suppression enhances the 18-hydroxycorticosterone and aldosterone response to metoclopramide in man

18-Hydroxycorticosterone (18-OHB) is a precursor of aldosterone and is the only corticosteroid, other than aldosterone, that is synthesized predominantly in the zona glomerulosa. Administration of the dopamine antagonist, metoclopramide results in parallel rises in plasma 18-OHB and aldosterone levels without affecting the plasma levels of other aldosterone precursors. However, 18-OHB is a product of the zona fasciculata as well as the glomerulosa. Thus, it is possible that metoclopramide may stimulate zona fasciculata secretion of 18-OHB. In order to more selectively examine dopaminergic regulation of zona glomerulosa secretion of 18-OHB we have examined the effect of glucocorticoid suppression of the fasciculata on the 18-OHB and aldosterone responses to metoclopramide, 10 mg iv in 6 normal volunteers. Dexamethasone, 2 mg every 6 hours for 5 days, suppressed basal levels of cortisol, corticosterone, 18-OHB and aldosterone. Dexamethasone treatment had no effect on basal levels of PRA or PRA responses to metoclopramide. The 18-OHB and aldosterone responses to metoclopramide were enhanced (p less than .05) by dexamethasone suppression. The results suggest that dopaminergic mechanisms selectively suppress glomerulosa production of 18-OHB. Endogenous ACTH may inhibit zona glomerulosa production of 18-OHB and aldosterone in response to the dopamine antagonist, metoclopramide.

Plasma concentrations of 18-hydroxycorticosterone and aldosterone in continuous ambulatory peritoneal dialysis and hemodialysis patients

This study explores the hypothesis that the continuous ultrafiltration that accompanies continuous ambulatory peritoneal dialysis (CAPD) produces greater activation of the renin-angiotensin aldosterone axis than does the intermittent ultrafiltration that accompanies thrice weekly hemodialysis (HD). Plasma renin activity (PRA), active renin (AR), total renin (TR), inactive renin (IR), 18-hydroxycorticosterone (18-OH-B), aldosterone (PAC), and cortisol were measured in plasma from CAPD (n = 6) and HD (n = 10) patients. Blood from CAPD patients was sampled at 8 AM after overnight recumbency and at 12 noon after four hours ambulation. Blood from HD patients was sampled immediately pre-HD (8 AM) and post-HD (12 noon) at both 8 AM and 12 noon. PRA (P less than 0.01), AR (P less than 0.01), and AR/TR (100%; P less than 0.01) were higher in CAPD than in HD. IR and TR were not different in the two groups. Plasma 18-OH-B was normal in HD but markedly elevated in CAPD. 18-OH-B was higher in CAPD than in HD at 8 AM (P less than 0.05) and at 12 noon (P less than 0.05). Plasma cortisol was not different in the two groups. We conclude that the greater degree of renin activation in CAPD versus HD contributes to the higher levels of 18-OH-B and PAC observed in CAPD patients.

Mineralocorticoid and prolactin response to the dopamine antagonist metoclopramide in patients with primary aldosteronism

Plasma mineralocorticoid and prolactin levels were evaluated before and 15, 30, 60 and 120 min after the administration of 10 mg metoclopramide in seven normotensive volunteers (42 +/- 5 (SD) years), as well as in ten patients with primary aldosteronism five with aldosterone-producing adenoma (49 +/- 4), and five with bilateral hyperplasia (47 +/- 3). Significant increases of plasma aldosterone, 18-hydroxycorticosterone (18-OH-B), and prolactin levels were observed in all normal subjects and in patients with primary aldosteronism after metoclopramide, whereas plasma 18-corticosterone, corticosterone, and cortisol levels as well as plasma renin activity did not change. The absolute increases of plasma aldosterone and 18-OH-B levels after metoclopramide were considerably higher in eight of the ten patients with primary aldosteronism. Furthermore, in patients with hyperplasia the maximum increase of aldosterone and 18-OH-B was delayed, as was the subsequent decrease of plasma aldosterone. Basal prolactin levels were within the normal range in all patients with primary aldosteronism, but the increase of prolactin observed 15 and 30 min after metoclopramide, was elevated in three patients with hyperplasia and in four patients with adenoma. For patients with primary aldosteronism, a positive correlation was found when the absolute maximum increase of plasma aldosterone levels after metoclopramide was plotted against the increase of prolactin (y = 1.11x - 101, r = 0.74, P less than 0.05). Our results suggest that prolactin, aldosterone, and 18-OH-B secretion is under increased inhibitory dopaminergic control in most of the patients with primary aldosteronism. The positive correlation between the metoclopramide-induced increase of plasma aldosterone and prolactin may indicate a common inhibitory dopaminergic mechanism, working on the pituitary and adrenal level.

Effect of metoclopramide on the secretion of aldosterone and other adrenocortical steroids

The aim of this study was to determine the effect of metoclopramide, a dopamine antagonist, on the secretion of aldosterone and other adrenocortical steroids in normal subjects. An i.v. bolus injection of 10 mg of metoclopramide significantly increased the plasma PRL, plasma aldosterone and 18-hydroxycorticosterone, but the plasma renin activity, plasma deoxycorticosterone, corticosterone and cortisol remained unchanged. The changes in plasma aldosterone induced by metoclopramide were significantly correlated with the basal levels of plasma aldosterone and renin activity. These results suggest that the response of plasma aldosterone to metoclopramide in normal subjects is influenced by the basal activity of renin-angiotensin-aldosterone system and the late step of aldosterone synthesis is stimulated by metoclopramide.

Dopaminergic modulation of corticosteroid responses to angiotensin II in man

This study was designed to investigate dopaminergic mechanisms involved in the control of corticosteroid secretion in man. Plasma cortisol, corticosterone, 11-deoxycorticosterone, 18-hydroxycorticosterone (18-OHB), and aldosterone responses to graded doses of angiotensin II and ACTH were evaluated in six healthy male volunteers with and without treatment with the dopamine agonist bromocriptine (BEC). Angiotensin II infusion resulted in parallel responses of 18-OHB and aldosterone without affecting other precursors of the aldosterone biosynthetic pathway. BEC (2.5 mg tid for 6 days) markedly suppressed basal supine plasma 18-OHB levels without affecting basal levels of aldosterone. Basal supine plasma corticosterone levels were increased after BEC treatment. BEC treatment inhibited the 18-OHB and aldosterone responses to graded infusions of angiotensin II. Plasma 18-OHB responses to ACTH infusion were not altered by BEC treatment. Other factors renin activity and serum electrolytes were not altered by BEC administration. These results suggest that angiotensin-mediated 18-OHB and aldosterone secretion is selectively inhibited by dopaminergic mechanisms.

Modulation of corticosteroid secretion by dopaminergic mechanisms in rhesus monkeys

This study was designed to investigate dopaminergic mechanisms in the control of corticosteroid secretion. Ten rhesus monkeys received metoclopramide (1.25 mg iv) or domperidone (1.25 mg iv) with 5% dextrose (vehicle) or with dopamine (4 micrograms.kg-1.min-1) infusions begun 60 min before administration of the dopamine antagonist. Metoclopramide, in the presence of vehicle, increased plasma 18-hydroxycorticosterone from 11.2 +/- 1.0 ng/dl to a maximum concentration of 50 +/- 5.1, plasma aldosterone from 5.4 +/- 0.7 ng/dl to a maximum of 38.2 +/- 4.9, and prolactin (PRL) concentrations from 8.5 +/- 1.2 ng/ml to a maximum of 114.6 +/- 7.2. Domperidone, in the presence of vehicle, increased plasma PRL concentrations from 8.6 +/- 1.2 ng/ml to a maximum of 148.7 +/- 7.8 but had no effect on plasma corticosteroids. Dopamine infusion inhibited the 18-hydroxycorticosterone, aldosterone, and PRL response to metoclopramide and the PRL response to domperidone. These results demonstrate that 18-hydroxycorticosterone and aldosterone responses to metoclopramide and PRL responses to metoclopramide and domperidone are mediated by their antagonist activity at dopamine receptors. Domperidone may fail to stimulate aldosterone secretion because it does not cross the blood-brain barrier or fails to act as an antagonist at the glomerulosa dopamine receptor through which dopaminergic modulation of corticosteroid secretion is mediated. A parallel time course of stimulation of 18-hydroxycorticosterone and aldosterone secretion without changes in other aldosterone precursors suggests that dopamine modulates the activity of the glomerulosa 18-hydroxylase enzyme.