Effect of serotonin4 (5-HT4) receptor agonists on aldosterone secretion in idiopathic hyperaldosteronism

Serotonin (5-HT) stimulates aldosterone secretion in man through 5-HT4 receptors positively coupled to adenylyl cyclase. In particular, it has been shown that oral administration of a single dose of the 5-HT4 receptor agonist cisapride induces a significant increase in plasma aldosterone levels (PAL) in healthy volunteers. Idiopathic hyperaldosteronism (IH) is a rare disorder characterized by hypertension, hypokalemia and bilateral adrenal hypersecretion of aldosterone. In patients with IH, administration of the 5-HT precursor 5-hydroxytryptophan (5-HTP) is followed by a significant increase in PAL. 5-HTP-induced aldosterone secretion has been attributed to the activation of central serotonergic pathways. The aim of the present study was to evaluate the effect of the oral administration of a single dose of cisapride (10 mg) on aldosterone secretion in 15 patients with IH, in a simple blind fashion versus placebo. Cisapride induced a significant increase in PAL but did not affect renin, cortisol and potassium levels. The present study demonstrates that 5-HT4 receptor agonists are able to stimulate aldosterone secretion in patients with IH. These data also indicate that hyperplastic glomerulosa tissue, like normal glomerulosa cells, expresses a functional 5-HT4 receptor. Therefore, 5-HT4 receptor antagonists may represent a new approach in the treatment of primary hyperaldosteronism.     

Study on clinical and endocrine characteristics of dexamethasone-suppressible hyperaldosteronism compared with those in primary aldosteronism owing to aldosterone-producing adenoma

The clinical and endocrine characteristics of 12 Japanese patients with dexamethasone-suppressible hyperaldosteronism were compared with those in 49 Japanese patients with primary aldosteronism due to aldosteronoma. The results were as follows: 1. Most of the laboratory data in the two groups were almost the same. 2. The grade of vascular damage in both uncontrolled (3) and well-controlled (9) patients with dexamethasone-suppressible hyperaldosteronism did not correlate with blood pressure response. 3. The responsiveness of plasma aldosterone to exogenous ACTH in 6 patients with dexamethasone-suppressible hyperaldosteronism was not different from that in 9 patients with aldosteronoma. Even in 3 well-controlled patients in the former group, the plasma aldosterone response was as low as in all the 3 patients with small aldosteronomas. 4. In 4 patients with small aldosteronomas, plasma aldosterone was continuously suppressed with daily dexamethasone to the same degree as in dexamethasone-suppressible hyperaldosteronism. 5. The blood pressure, however, did not improve even in the patients with small aldosteronomas. The possible indistinguishable mechanism in dexamethasone-suppressible hyperaldosteronism and primary aldosteronism with small adenomas and the role of unknown hypertensinogenic steroid(s) other than aldosterone in inducing hypertension in dexamethasone-suppressible hyperaldosteronism are discussed.     

Effects of a serotonin 5-HT(4) receptor antagonist SB-207266 on gastrointestinal motor and sensory function in humans

BACKGROUND: Serotonin 5-HT(4) receptors are located on enteric cholinergic neurones and may regulate peristalsis. 5-HT(4) receptors on primary afferent neurones have been postulated to modulate visceral sensation. While 5-HT(4) agonists are used as prokinetic agents, the physiological role of 5-HT(4) receptors in the human gut is unknown. AIMS: Our aim was to characterise the role of 5-HT(4) receptors in regulating gastrointestinal motor and sensory function in healthy subjects under baseline and stimulated conditions with a 5-HT(4) receptor antagonist. METHODS: Part A compared the effects of placebo to four doses of a 5-HT(4) receptor antagonist (SB-207266) on the cisapride mediated increase in plasma aldosterone (a 5-HT(4) mediated response) and orocaecal transit in 18 subjects. In part B, 52 healthy subjects received placebo, or 0.05, 0.5, or 5 mg of SB-207266 for 10-12 days; gastric, small bowel, and colonic transit were measured by scintigraphy on days 7-9, and fasting and postprandial colonic motor function, compliance, and sensation during distensions were assessed on day 12. RESULTS: Part A: 0.5, 5, and 20 mg doses of SB-207266 had significant and quantitatively similar effects, antagonising the cisapride mediated increase in plasma aldosterone and acceleration of orocaecal transit. Part B: SB-207266 tended to delay colonic transit (geometric centre of isotope at 24 (p=0.06) and 48 hours (p=0.08)), but did not have dose related effects on transit, fasting or postprandial colonic motor activity, compliance, or sensation. CONCLUSION: 5-HT(4) receptors are involved in the regulation of cisapride stimulated orocaecal transit; SB 207266 tends to modulate colonic transit but not sensory functions or compliance in healthy human subjects.     

Abnormal sensitivity of cortisol-producing adrenocortical adenomas to serotonin: in vivo and in vitro studies

Two patients with incidentally discovered adrenocortical adenomas underwent a series of pharmacological and physiological tests after pretreatment with dexamethasone. Illicit plasma cortisol responses to the serotonin (5-HT)4 receptor agonist cisapride were observed in the two patients. Significant increases in plasma cortisol levels were also noticed after glucagon and combined TRH/GnRH/GHRH stimulation tests in patient 1 and after administration of the lysine vasopressin precursor terlipressin in patient 2. After adrenalectomy, in vitro studies were conducted to investigate the cortisol responses of cultured tumor cells to serotonergic ligands and peptide hormones. In the two cases, 5-HT stimulated cortisol secretion from tumor cells with increased efficacy and/or potency to activate steroidogenesis by comparison with normal adrenocortical cells. The corticotropic effect of 5-HT was inhibited by the specific 5-HT4 receptor antagonist GR 113808 and more potently by methiothepin, a nonspecific serotonergic antagonist having no affinity for the 5-HT4 receptor. These results show that the hypersensitivity of the tumors to 5-HT was related to tissue expression of an ectopic serotonergic receptor in addition to the eutopic 5-HT4 receptor. In the two adenoma tissues, immunohistochemical studies revealed the presence of 5-HT-like immunoreactivity within clusters of steroidogenic cells, suggesting that 5-HT acted through an autocrine/paracrine mechanism to stimulate steroidogenesis. Glucagon and GnRH but not TRH, GHRH, and human chorionic gonadotropin stimulated cortisol secretion from tumor 1 cells. In conclusion, this study provides the first observation of adrenocortical cortisol-producing adenomas hypersensitive in vivo and in vitro to serotonergic agonists. Our results also show that cortisol-producing adenomas can express simultaneously several illegitimate receptors.     

Production and metabolism of serotonin (5-HT) by the human adrenal cortex: paracrine stimulation of aldosterone secretion by 5-HT

In the human adrenal cortex, serotonin (5-HT) is contained in mast-like cells, and we have shown that 5-HT stimulates aldosterone secretion, suggesting that 5-HT may control glomerulosa cells through a paracrine mechanism. Concurrently, the presence of 5-hydroxyindolacetic acid in human adrenocortical extracts indicates that 5-HT may be metabolized after local release by mast cells. The aim of the present study was to investigate in vitro the production and metabolism of 5-HT by the human adrenal cortex. Perifused adrenal slices released spontaneously detectable amounts of 5-HT (0.74 +/- 0.38 fmol/mg wet tissue.min). The mast cell-depleting drug compound 48/80 induced a burst of 5-HT secretion followed by a gradual increase in aldosterone production. Administration of the specific 5-HT(4) receptor antagonist GR 113808 (10(-6) M) did not affect compound 48/80-induced 5-HT release but abolished the stimulatory effect of compound 48/80 on aldosterone secretion, indicating that 5-HT released locally is responsible for a paracrine control of steroidogenesis. Incubation of cells from the human adrenal cortex with 5-HT (10(-5) M) provoked the formation of the 5-HT metabolite 5-hydroxytryptophol. The type A monoamine oxidase (MAO) inhibitor clorgyline (10(-6) M) suppressed the metabolism of 5-HT into 5-hydroxytryptophol. Immunocytochemical staining of cultured cells revealed the presence of a subpopulation of MAO-A-positive cells. Double labeling with an antiserum against chromogranin A showed that MAO-A was actually contained in chromaffin cells. Similarly, immunohistochemical staining of adrenal slices showed that MAO-A was expressed in chromaffin cells located both in the medulla and in intracortical rays. In conclusion, the present study shows that, in the human adrenal cortex, 5-HT, released by mast-cells, may stimulate aldosterone secretion in a paracrine manner. Our data also indicate that 5-HT is metabolized by MAO-A located in intracortical chromaffin cells.     

Preoperative lateralisation of aldosteronomas by aldosterone/cortisol ratios in adrenal venous plasma

Data from adrenal scintigraphy with 6 beta-[131I]-iodomethyl-19-norcholesterol (AS), computed tomography (CT), adrenal venography and adrenal venous sampling were compared for their accuracy in locating small aldosteronomas in 17 patients. Final confirmation of location was by surgery. Seventeen out of 18 adrenals whose aldosterone/cortisol (A/C) ratio was 5.0 x 10(-3) or higher were found to have aldosteronomas (94.4%). All 14 adrenals whose A/C ratios were less than 5.0 x 10(-3) contained no aldosteronomas (100%). AS successfully lateralised nine out of 17 aldosteronomas (52.9%), CT 3 out of 5 (60.0%), adrenal venography 12 out of 17 (70.6%), adrenal venous aldosterone concentration 12 out of 15 (80.0%). The most frequent problem with adrenal venous sampling was the varying degrees of mixture with non-adrenal venous blood, mainly from renal vein and inferior vena cava blood. The A/C ratio of adrenal venous plasma proved to be the most useful diagnostic tool, using cortisol concentration as an indicator of any non-adrenal venous mixture.     

Effects of serotonin and vasopressin on cortisol production from an adrenocortical tumor causing subclinical Cushing's syndrome

In dexamethasone-suppressed healthy volunteers, the serotonin4 (5-HT4) receptor agonist cisapride and lysine vasopressin [LVP, an analog of arginine vasopressin (AVP)] have no influence on plasma cortisol levels (PCL). In contrast, cisapride and AVP have been shown to stimulate cortisol secretion in patients with adrenal tumor or bilateral adrenal hyperplasia and Cushing's syndrome. In this report, we describe a case of adrenocortical adenoma causing subclinical Cushing's syndrome. Cisapride and terlipressin, a precursor of LVP, both induced an increase in PCL reaching +88% and +100%, respectively, without any significant variation of plasma ACTH levels. In vitro experiments were conducted to investigate the effects of 5-HT and AVP on cortisol production from cultured tumor cells and normal adrenocortical cells. 5-HT and AVP both induced a dose-dependent increase in cortisol production from cultured tumor cells. Comparison of the data obtained with tumor and normal cells, respectively, showed that 5-HT was more efficient to stimulate steroidogenesis in adenomatous than normal cells. Concurrently, the efficacy and potency of AVP were both higher in tumor than normal cells. Collectively, these results show that the abnormal in vivo responses of the adrenocortical adenoma to cisapride and LVP could be ascribed to an increased sensitivity of the tumor tissue to 5-HT and AVP. The data also suggest that the adrenocortical tumor overexpressed eutopic 5-HT4 and V1 receptors.     

Aberrant membrane hormone receptors in incidentally discovered bilateral macronodular adrenal hyperplasia with subclinical Cushing's syndrome.

Cortisol secretion in adrenal Cushing's syndrome can be regulated by the aberrant adrenal expression of receptors for gastric inhibitory polypeptide, vasopressin, catecholamines, LH/human CG (LH/hCG), or serotonin. Four patients with incidentally discovered bilateral macronodular adrenal hyperplasia without clinical Cushing's syndrome were evaluated for the possible presence of aberrant adrenocortical hormone receptors. Urinary free cortisol levels were within normal limits, but plasma cortisol levels were slightly elevated at nighttime and suppressed incompletely after dexamethasone administration. Plasma ACTH was partially suppressed basally but increased after administration of ovine CRH. A 51-yr-old woman had ACTH-independent increases of plasma cortisol after 10 IU AVP im (292%), 100 microg GnRH iv (184%), or 10 mg cisapride orally (310%); cortisol also increased after administration of NaCl (3%), hCG, human LH, and metoclopramide. In a 61-yr-old man, cortisol was increased by AVP (349%), GnRH (155%), hCG (252%), and metoclopramide (191%). Another 53-yr-old male increased plasma cortisol after AVP (171%) and cisapride (142%). Cortisol secretion was also stimulated by vasopressin in a 54-yr-old female. This study demonstrates that subclinical secretion of cortisol can be regulated via the aberrant function of at least V1-vasopressin, LH/hCG, or 5-HT4 receptors in incidentally identified bilateral macronodular adrenal hyperplasia.     

The functional HERG variant 897T is associated with Conn's adenoma

OBJECTIVE: Aldosterone secreting adenomas (aldosteronomas) have an unknown molecular origin. Ion channel currents are involved in signal transduction leading to aldosterone synthesis and secretion. HERG (human-ether-a-go-go-related gene) encodes for a potassium channel responsible for the outward rectifying delayed current and it is mutation prone. When mutated it causes most of the familial forms of both long QT and short QT syndromes. Abnormal repolarization in glomerulosa cells might increase aldosterone secretion or induce a proliferative advantage. The aims of this study were to: (1) evaluate HERG expression in aldosteronomas; (2) search for HERG somatic mutations; and (3) determine whether there is any relationship between the common HERG functional variant (A2690C, leading from lysine 897 to threonine, K897T) and aldosteronoma. DESIGN AND METHODS: Aldosteronoma and blood samples from 17 patients were studied to evaluate HERG expression, full-length HERG complementary DNA sequencing, and genotyping for K897T alleles. The prevalence of HERG 897 alleles was also tested in a control population and a population consisting entirely of hypertensive individuals. RESULTS: HERG was expressed in all aldosteronomas analysed. HERG somatic mutations were not detected. The 897T variant of HERG was significantly more common among patients with aldosteronoma (897T allele 41%) than in patients with moderate-severe essential hypertension (897T allele 20%, P = 0.007) or in the control population (897T allele 12%, P < 0.0001). The 897T/T genotype was present in 24% of the aldosteronoma patients versus 7% (P = 0.040) and 3% (P = 0.001) in essential hypertension and in the control population, respectively. When the chi test was performed considering the three groups together, the significance was similar (for alleles P < 0.0001 and for genotypes P = 0.004). CONCLUSION: The common functional HERG variant 897T may predispose to the development of aldosteronoma.     

Activation of 5-HT(7) receptor in rat glomerulosa cells is associated with an increase in adenylyl cyclase activity and calcium influx through T-type calcium channels

Serotonin (5-HT) stimulates aldosterone secretion from the rat adrenal gland through 5-HT(7) receptors. The aim of the present study was to investigate the transduction mechanisms associated with activation of 5-HT(7) receptors in rat glomerulosa cells. The stimulatory effect of 5-HT on aldosterone secretion and cAMP formation was significantly reduced by the 5-HT(7) receptor antagonist LY 215840. Pretreatment of cells with the adenylyl cyclase inhibitor SQ 22536 or the PKA inhibitor H-89 markedly attenuated the effect of 5-HT on aldosterone secretion. Conversely, type 2 and 4 phosphodiesterase inhibitors potentiated the 5-HT-induced stimulation of aldosterone secretion. Administration of 5-HT in the vicinity of cultured glomerulosa cells induced a slowly developing and robust increase in cytosolic calcium concentration ([Ca(2+)](i)). The effect of 5-HT on [Ca(2+)](i) was suppressed by mibefradil, a T-type calcium channel blocker. Patch-clamp studies confirmed that 5-HT activated a T-type calcium current. Mibefradil also induced a dose-dependent inhibition of 5-HT-induced aldosterone secretion. The sequence of events associated with activation of 5-HT(7) receptors was investigated. The PKA inhibitor H-89 markedly attenuated both the [Ca(2+)](i) response and the activation of T-type calcium current induced by 5-HT. In contrast, reduction of the calcium concentration in the incubation medium did not affect 5-HT- induced cAMP formation. Preincubation of glomerulosa cells with cholera toxin abolished the stimulatory effect of 5-HT on aldosterone secretion, but pertussis toxin had no effect. Taken together, these data demonstrate that, in rat glomerulosa cells, activation of native 5-HT(7) receptors stimulates cAMP formation through a G(salpha) protein, which in turn provokes calcium influx through T-type calcium channels. Both the adenylyl cyclase/PKA pathway and the calcium influx are involved in 5-HT-induced aldosterone secretion.     

Involvement of T-type calcium channels in the mechanism of action of 5-HT in rat glomerulosa cells: a novel signaling pathway for the 5-HT7 receptor

We have previously demonstrated that, in rat, the stimulatory effect of 5-HT on aldosterone secretion is mediated through a 5-HT7 receptor subtype. The aim of the present study was to characterize the transduction mechanisms associated with activation of native 5-HT7 receptors. 5-HT induced a dose-dependent increase in cAMP production in rat glomerulosa cells. Pretreatment of cells with the adenylyl cyclase (AC) inhibitor SQ 22536 or the protein kinase A (PKA) inhibitor H-89 markedly attenuated the effect of 5-HT on aldosterone secretion. Administration of 5-HT in the vicinity of glomerulosa cells induced a robust increase in cytosolic calcium concentration ([Ca2+]i) and this effect was abrogated by the T-type calcium channel blocker mibefradil. Patch-clamp studies confirmed that 5-HT activated a T-type calcium current. H-89 attenuated both the [Ca2+]i response and the activation of T-type calcium current induced by 5-HT. Reduction of extracellular calcium concentration in the medium or administration of mibefradil caused a marked reduction of the maximum effect (Emax) of 5-HT on aldosterone secretion. These data demonstrate that activation of native 5-HT7 receptors stimulates cAMP formation, which in turn provokes calcium influx through T-type calcium channels. Both the activation of the AC/PKA pathway and the calcium influx are involved in 5-HT-induced aldosterone secretion.     

Luteinizing hormone (LH)-responsive Cushing's syndrome: the demonstration of LH receptor messenger ribonucleic acid in hyperplastic adrenal cells,which respond to chorionic gonadotropin and serotonin agonists in vitro

In a substantial part of adrenal adenomas and hyperplasias from patients with Cushing's syndrome, cortisol production is controlled by the expression of aberrant hormone receptors on adrenocortical cells. We present in vivo and in vitro data of two patients with a LH-responsive Cushing's syndrome based on ACTH-independent bilateral adrenal hyperplasia. Patients 1 and 2 are women who presented with Cushing's syndrome and bilateral adrenal hyperplasia. Endocrine testing demonstrated absence of cortisol diurnal rhythm, insufficient cortisol suppression after 1 mg dexamethasone orally, and undetectable ACTH levels in both patients. Both patients were treated by laparoscopic biadrenalectomy. In in vivo testing, in patients 1 and 2, a profound cortisol rise was found after administration of GnRH [change in cortisol (Delta F), 118 and 106%, respectively], human CG (Delta F, 133 and 44%), LH (Delta F, 73 and 43%), ACTH (Delta F, 89 and 181%), and the 5-hydroxy-tryptamine receptor type 4 (5-HT(4)) agonists cisapride (Delta F, 141 and 148%) and metoclopramide (Delta F, 189 and 95%). In in vitro testing, adrenal cells from patient 2 responded, in a dose-dependent fashion, with cortisol production after exposure to human CG (Delta F, 45%), cisapride (Delta F, 68%), and metoclopramide (Delta F, 81%). ACTH induced cortisol production by cells from both patients (Delta F, 135 and 159%). In receptor studies, LH receptor mRNA was demonstrated in adrenal tissue of both patients but also in control adrenal tissue of two patients with persisting pituitary-dependent Cushing's syndrome treated by biadrenalectomy. In neither patient were mutations found in the ACTH receptor gene. LH-responsive Cushing's syndrome associated with bilateral adrenal hyperplasia may result from aberrant (or possibly increased) adrenal LH receptor expression. This variant is further characterized by adrenal responsiveness to 5-HT4 receptor agonists, possibly pointing to an interaction between LH and serotonin in the regulation of cortisol secretion. Despite the regulatory potential of LH and 5-HT4 receptor agonists on cortisol production in our patients, their adrenals seemed to be still sensitive to ACTH, both in vivo and in vitro.     

Rat glomerulosa cells express functional 5-HT7 receptors

It has been previously demonstrated that serotonin (5-HT) is a potent stimulator of aldosterone secretion in amphibians and mammals. The aim of the present study was to characterize the type of serotonergic receptor involved in the action of 5-HT on rat glomerulosa cells. The effects of 10 serotonergic receptor agonists and 12 receptor antagonists on aldosterone secretion from perifused rat adrenocortical slices were investigated. Correlation analysis between the potencies of the different compounds in our model and those previously reported for transfected 5-HT receptors showed that the rat adrenal 5-HT receptor exhibits the pharmacological profile of the 5-HT7 receptor. RT-PCR amplification with specific primers for the 5-HT7 receptor confirmed the presence of 5-HT7 receptor mRNA in the adrenal cortex. Western blot analysis using antibodies against the 5-HT7 receptor revealed the occurrence of a protein with an apparent molecular mass of 66 kDa in the zona glomerulosa. In glomerulosa cells, 5-HT induced a concentration-dependent increase of cAMP formation. These data demonstrate that rat adrenal glomerulosa cells express functional 5-HT7 receptors positively coupled to adenylyl cyclase.     

Overexpression of serotonin4 receptors in cisapride-responsive adrenocorticotropin-independent bilateral macronodular adrenal hyperplasia causing Cushing's syndrome

The serotonin4 (5-HT4) receptor agonists cisapride and/or metoclopramide have been shown to stimulate cortisol secretion in some patients with ACTH-independent bilateral macronodular adrenal hyperplasias (AIMAH) causing Cushing's syndrome. In the present study, we have investigated quantitatively and qualitatively the expression of the 5-HT4 receptor in both normal adrenal cortex and tissues removed from six patients (P1-P6) with cisapride-responsive AIMAH and Cushing's syndrome. Real-time quantitative PCR assay revealed that the 5-HT4 receptor was overexpressed in four of the six hyperplasias studied when compared with normal adrenal cortex. In these tissues, 5-HT4 receptor mRNA expression was 3 to 16 times higher than in normal glands, likely explaining the abnormal in vivo cortisol response to cisapride. Characterization of 5-HT4 receptor splice variants by RT-PCR in both hyperplastic and normal adrenals showed that the variants present in the two hyperplasias that did not overexpress the 5-HT4 receptor, i.e. P2 and P5, could also be detected in the normal adrenal tissue. In addition, sequencing of the full-length cDNAs encoding 5-HT4 receptors in hyperplasias P2 and P5 did not reveal any mutation. Taken together, our results show an overexpression of the 5-HT4 receptor in cisapride-responsive AIMAH. However, in two cases, the level of expression of the receptor in the hyperplastic adrenal cortex was similar to that of normal adrenal gland. The enhanced sensitivity of these two tissues to 5-HT4 receptor agonists was not due to ectopic expression of 5-HT4 receptor isoforms or to the occurrence of somatic gain-of-function mutation of the receptor.     

Calcitonin gene-related peptide is an inhibitor of aldosterone secretion

This study examined the effects of calcitonin gene-related peptide (CGRP) on aldosterone secretion both in vivo and in vitro. Intravenous administration of CGRP (0.01 micrograms/kg) in 6 conscious dogs produced a significant decrease in plasma aldosterone concentration from 68 +/- 12 pg/ml to 28 +/- 11 pg/ml (p less than 0.05) despite a mild but significant elevation of plasma renin activity. In an in vitro study using isolated rabbit adrenal glomerulosa cells CGRP reduced the basal aldosterone secretion in a dose-related manner and furthermore 10(-9) M CGRP inhibited the aldosterone secretion stimulated by 10(-8) M angiotensin II. From these results it is suggested that CGRP has an inhibitory effect on aldosterone secretion.     

In vitro evidence for local generation of renin and angiotensin II/III immunoreactivity by the human adrenal gland

The adrenal gland of various mammalian species has been shown to contain all the components of a functional renin-angiotensin system. We investigated the existence of this local system in human adrenal tissues surgically obtained. Eight normal adrenals (cortex and medulla) and 6 aldosterone-producing adenomas (aldosteronomas) were examined. Minced tissues were superfused over 270 min, and 15-min fractions were collected. In the perfusates, active renin was measured by immunoradiometric assay with human anti-renin monoclonal antibodies; immunoreactive angiotensin II/III and aldosterone were measured by radioimmunoassay. Adrenal tissues, either normal or pathological, were found concomitantly to release renin, angiotensin II/III and aldosterone. The pattern of this spontaneous release exhibited a pulsatile character. The total amount of renin and angiotensin II/III secreted during superfusion clearly exceeded the tissue content (determined by extraction). Addition of the angiotensin-converting enzyme inhibitor quinaprilat (4 x 10(-6) mol/l) in the superfusion caused a concomitant decrease of angiotensin II/III and aldosterone secretion by 3 normal tissues, and no change in 2 aldosteronomas. These data provide evidence that the human adrenal gland in vitro generates and releases both renin and angiotensin II/III, and support the hypothesis that locally formed angiotensin II/III may play a role as a paracrine regulator of physiological aldosterone secretion.     

The effect of metoclopramide and dopamine on mineralocorticoid secretion--in vivo and in vitro studies

There is considerable information suggesting that dopamine is a physiological regulator of aldosterone secretion. Metoclopramide, a specific dopamine antagonist, elicits a rapid rise in plasma aldosterone independent of the known aldosterone-regulating factors. However, the mechanism and the site of action of metoclopramide, whether adrenal or extra-adrenal, in stimulation of aldosterone production remain to be defined. The present studies were designed to investigate the mechanism of dopaminergic control of corticosteroid secretion and to determine at which step in the aldosterone biosynthetic pathway metoclopramide and dopamine exert their effect. Plasma concentrations of progesterone, 11-deoxycorticosterone (DOC), and cortisol were not altered by a bolus intravenous administration of 10 mg metoclopramide in 8 healthy male volunteers. Metoclopramide increased plasma aldosterone from 6.9 +/- 2.8 (Mean +/- 2SD) ng/100 ml to a maximum level of 18.2 +/- 4.7 ng/100 ml, 18-hydroxycorticosterone (18-OHB) from 12.6 +/- 6.5 ng/100 ml to a maximum of 41.3 +/- 7.3 ng/100 ml and corticosterone from 0.36 +/- 0.09 microgram/100 ml to a maximum of 0.85 +/- 0.22 microgram/100 ml. The aldosterone, 18-OHB and corticosterone responses displayed a parallel time course, with a significant response of each occurring within 5 minutes after metoclopramide administration. These data suggest that metoclopramide may modulate the activities of 18-hydroxylase and 11 beta-hydroxylase. Studies in vitro revealed that metoclopramide (10(-8)-10(-4) M had little effect on basal production of aldosterone, 18-OHB and corticosterone from human adrenal slices. Dopamine (10(-4) M) did not alter the basal secretion of aldosterone, 18-OHB and corticosterone, but suppressed the secretion of these 3 mineralocorticoids by ACTH, which were diminished by addition of 10(-4) M metoclopramide. There was a concentration-dependent inhibitory effect of dopamine on conversion of corticosterone to 18-OHB and DOC to corticosterone in vitro using bovine adrenal mitochondrial fractions. IC50 of dopamine inhibiting 18-hydroxylation and 11 beta-hydroxylation were 7.5 X 10(-7) M and 9.5 X 10(-4) M, respectively. It appears that physiological concentration of dopamine can modulate the activity of 18-hydroxylase enzyme. In summary, it can be concluded that the in vivo and in vitro studies are compatible with a view that dopamine has a physiological role in the regulation of aldosterone by modulating the activity of 18-hydroxylase enzyme.