Effect of metoclopramide on aldosterone and regulatory factors in man

Dopamine and sympathoadrenal activity in man

The sympathetic adrenal (SA) activity can be modulated by dopamine (DA) through D2 receptors. In man, using D2 antagonists, it has been demonstrated that endogenous DA plays an inhibitory modulation of the SA system during high degree of SA activation. D2 agonists are able to induce a decrease in norepinephrine (NE) release either in vitro or in vivo. This effect leads, in vivo, to a decrease in blood pressure (BP) and to an activation of arterial baroreceptors. Therefore, in vivo, the D2 mediated inhibition of epinephrine (E) release, which is clearly demonstrated in vitro, is overwhelmed by the baroreceptor-mediated activation of the splachnic nerve. As a consequence, the in vivo administration of D2 agonists can induce a different effect on the net peripheral sympathetic tone of an organ, depending on the balance between the degree of the baroreceptor-mediated sympathetic activation and the inhibitory D2-mediated inhibition of NE release at the tissue level. In the present paper we investigated the in vivo effect of placebo (PL) or acute oral bromocriptine (BC) administration on plasma CA and on the cardiac sympatho-vagal balance of 7 normal volunteers, as assessed by power spectral analysis of heart rate (HR) variability (autoregressive method), either in resting or sitting position. Low frequency (LF) and high frequency (HF) components, both expressed in normalized units (nU), and LF/HF ratio were calculated. BC caused a decrease in BP, plasma NE and no change in HR in resting and sitting position. Plasma E increased in sitting position. At the heart level, after BC, we observed, during rest, an increase in LF and LF/HF ratio and a decrease in HF while in sitting position LF did not increase further. These data show that BC, while reducing BP through a decrease of plasma NE, increases LF/HF ratio (sympathetic tone) without any change in heart rate. These data seem to confirm that BC causes an inhibitory modulation of the SA system acting predominantly at the periphery through D2 presynaptic receptors.

Atrial natriuretic peptide in volume expansion-induced natriuresis in man

The role of atrial natriuretic peptide (ANP) in the extracellular volume expansion (ECVE) induced natriuresis was examined in normal man under basal conditions and following dopamine blockage. Hypotonic ECVE was induced by drinking of 20 ml/kg tap water and subsequent intravenous infusion of 2 1 0, 9% saline over a period of 4 hours. This maneuver caused an increase in the plasma concentrations of ANP from 25.8 +/- 3.4 (means +/- SEM) to 59.7 +/- 6.7 fmol/ml. There was a dissociation between ANP response and urinary sodium excretion. A transient rise in glomerular filtration rate (GFR), plasma dopamine and a continuous decrease in plasma renin activity, aldosterone, vasopressin, and noradrenaline were observed. The natriuretic response to ECVE was blunted during dopamine blockade by metoclopramide, but plasma ANP, renin activity, catecholamine and vasopressin levels were not affected. However, plasma aldosterone rose. Our data are compatible with the concept that intrarenal dopamine and raised plasma concentration of ANP contribute to the natriuretic response to ECVE, but these hormonal changes do not completely explain the underlying mechanisms.

Zinc content in epididymal spermatozoa of metoclopramide-treated rats

Zinc content was determined separately in spermatozoa taken from epididymal caput and cauda in rats. It was revealed that spermatozoa transported from the epididymal caput to the cauda reduce about 54% of zinc. This reduction is significantly inhibited in spermatozoa of rats receiving metoclopramide. That is also accompanied by a fall of testosterone level in blood serum and of delta 5, 3 beta-HSD activity in Leydig cells. It was found out that the reduction of zinc in spermatozoa at the time of their passage through the epididymis is the process that depends on androgens.

Effect of metoclopramide on adrenal secretion in sheep: influence of dexamethasone and sodium intake

Metoclopramide, a competitive dopamine antagonist, stimulates aldosterone in man and monkey without affecting cortisol secretion. In sheep, metoclopramide also stimulates aldosterone but ist action on adrenocortical secretion is more controversial. To clarify the action of metoclopramide in conscious sheep, the response of plasma aldosterone, cortisol, angiotensin II and potassium were studied after 0.16 and 0.64 mg/kg metoclopramide, with and without pretreatment with dexamethasone. The effect of sodium status on the response was also studied by repeating the experiments after 7 days of dietary sodium restriction. In the absence of dexamethasone, plasma aldosterone was significantly increased by metoclopramide in both sodium-replete and restricted sheep. In sodium-replete sheep, plasma cortisol was also increased by 0.64 mg/kg, and by both doses when salt-restricted. However all cortisol responses were completely suppressed by dexamethasone pretreatment. Dexamethasone also suppressed the aldosterone response to metoclopramide in sodium-replete but not in sodium-restricted sheep where significant responses of aldosterone to both doses of metoclopramide still occurred without changes in plasma angiotensin II or potassium. While a nonspecific stress effect of metoclopramide can contribute to the aldosterone response, these results show that the sheep's adrenal glomerulosa is capable of responding to metoclopramide without change in ACTH, angiotensin or potassium.

Arterial hypertension in acromegaly: altered dopaminergic control of aldosterone secretion

In order to elucidate the role of the dopaminergic system in the control of aldosterone secretion in acromegaly with arterial hypertension 10 patients and 10 healthy volunteers were studied. Plasma aldosterone and prolactin were determined by radioimmunological methods after dopaminergic receptor blockade with metoclopramide and sulpiride. Plasma aldosterone was also determined after adrenal stimulation with synthetic corticotrophin (Synacthen). In patients with acromegaly and hypertension, the aldosterone secretion in response to metoclopramide was completely inhibited whereas induced with corticotrophin was lower than in controls. Also prolactin secretion in response to metoclopramide or sulpiride was markedly lower as compared with that in controls. Sulpiride did not stimulate aldosterone secretion either in patients or in healthy controls. The results indicate that the dopaminergic control of aldosterone secretion in acromegaly with arterial hypertension is altered.

Metoclopramide--a review

Metoclopramide has wide applications in both clinical and experimental medicine. It is useful in the management of gastro-oesophageal reflux and gastric stasis. It is being used increasingly in the management of nausea and vomiting, and at high doses will significantly relieve the emesis that is induced by cytotoxic agents. Metoclopramide also has an important place in the investigation of the role of dopamine in physiological and pathological processes.

Effect of fenoldopam on the aldosterone response to metoclopramide in man

The effect of fenoldopam, a selective DA1-agonist, on the plasma aldosterone response to metoclopramide was studied in six hypertensive patients included in a multicentre double-blind placebo controlled cross-over study of the antihypertensive effects of fenoldopam. Fenoldopam significantly increased baseline plasma renin activity (PRA); baseline plasma aldosterone levels rose slightly. Baseline PRL and the PRL response to metoclopramide were not altered by fenoldopam. After metoclopramide, a significant increase of plasma aldosterone was observed during treatment with fenoldopam, as well as in the placebo-period. The peak values were not significantly different and occurred at 15 min during both treatment periods. These results indicate that fenoldopam does not reduce metoclopramide-induced aldosterone secretion and therefore suggest that the adrenal dopamine receptor is not identical to the vascular DA1 receptor.

Does endogenous dopamine modulate human sympathetic activity through DA2 receptors?

The effects of placebo and DA2 antidopaminergic agents on basal and stimulated catecholamine (CA) plasma levels in humans have been evaluated by administration either of domperidone or metoclopramide to separate groups of subjects. The latter group was subjected domperidone to sympathetic stimulation by handgrip coldpressor tests, and standing. Pharmacological DA2 receptor blockade, either peripheral by or central and peripheral by metoclopramide, did not modify plasma CA whilst resting or during acute sympathetic stimulation. It is concluded that endogenous dopamine does not seem to play a significant role in modulating NE release in man, at least not under the physiological conditions examined.

Stimulation of aldosterone secretion by metoclopramide is not affected by chronic converting enzyme inhibition

To assess if dopaminergic control of aldosterone secretion is mediated by the renin-angiotensin system, the effect of chronic angiotensin converting enzyme inhibition by enalapril on the aldosterone response to metoclopramide has been studied in 10 patients with mild to moderate essential hypertension. Enalapril reduced supine blood pressure and increased the heart rate significantly. Plasma renin activity and urinary sodium excretion rose significantly. PRA was not changed by metoclopramide, neither during placebo nor during enalapril treatment. Metoclopramide induced a two-fold increase in plasma aldosterone, the peak response being reached within 15 min. Enalapril treatment did not alter the aldosterone response to metoclopramide. Dopaminergic control of aldosterone secretion appears to be independent of the renin-angiotensin system.