Serotonin stimulates corticosteroid secretion by frog adrenocortical tissue in vitro

Serotonin directly stimulates cortisol secretion from the interrenals in goldfish

While serotonin (5-HT) can stimulate the hypothalamic-pituitary-interrenal stress axis in fish, the specific site(s) of 5-HT action are poorly understood. In this study, goldfish (Carassius auratus) were injected intraperitoneally with either saline or the 5-HT1A/7 receptor agonist 8-OH-DPAT at a dose of 100 or 400 μg/kg body weight and sampled 1.5 and 8 h post-injection. Relative to unhandled controls, the saline and 100 μg/kg 8-OH-DPAT treatments elicited similar transient 5- to 7-fold increases in plasma cortisol and the 400 μg/kg 8-OH-DPAT dosage resulted in a sustained 16-fold increase in cortisol levels. Although the 5-HT1A receptor is expressed in the brain preoptic area (POA), the pituitary and the head kidney, neither the saline nor the 8-OH-DPAT treatments affected the mRNA abundance of POA corticotropin-releasing factor and pituitary pro-opiomelanocortin or plasma adrenocorticotropic hormone (ACTH) levels. To assess the direct actions of 5-HT on cortisol secretion relative to those of ACTH, head kidney tissue were superfused with 10(-7)M 5-HT, ACTH or a combined 5-HT/ACTH treatment. Overall, the ACTH and 5-HT/ACTH treatments resulted in higher peak cortisol and total cortisol release than in the 5-HT treatment but the response time to peak cortisol release was shorter in the combined treatment than in either the 5-HT or ACTH alone treatments. Both 8-OH-DPAT and cisapride, a 5-HT4 receptor agonist, also stimulated cortisol release in vitro and their actions were reversed by selective 5-HT1A and 5-HT4 receptor antagonists, respectively. Finally, double-labeling with anti-tyrosine hydroxylase and anti-5-HT revealed that the chromaffin cells of the head kidney contain 5-HT. Thus, in goldfish, 5-HT can directly stimulate cortisol secretion from the interrenals via multiple 5-HT receptor subtypes and the chromaffin cells may be involved in the paracrine regulation of cortisol secretion via 5-HT.

Elevated cortisol inhibits adrenocorticotropic hormone- and serotonin-stimulated cortisol secretion from the interrenal cells of the Gulf toadfish (Opsanus beta)

Stimulation of the toadfish 5-HT(1A) receptor by serotonin (5-hydroxytryptamine; 5-HT) or 8-OH-DPAT, a 5-HT(1A) receptor agonist, results in a significant elevation in plasma cortisol. Conversely, chronic elevation of plasma cortisol has been shown to decrease brain 5-HT(1A) receptor mRNA and protein levels via the glucocorticoid receptor (GR); however, there appears to be a disconnect between brain levels of the receptor and cortisol release. We hypothesized that elevated plasma cortisol would inhibit both adrenocorticotropic hormone (ACTH)- and 5-HT-stimulated cortisol release from the interrenal cells of Gulf toadfish, that ACTH sensitivity would not be GR-mediated and 5-HT-stimulated cortisol release would not be via the 5-HT(1A) receptor. To test these hypotheses, interrenal cells from uncrowded, crowded, vehicle-, and cortisol-implanted toadfish were incubated with either ACTH, 5-HT or 5-HT receptor agonists, and cortisol secretion was measured. Incubation with ACTH or 5-HT resulted in a stimulation of cortisol secretion in uncrowded toadfish. Cortisol secretion in response to ACTH was not affected in crowded fish; however, interrenal cells from cortisol-implanted toadfish secreted significantly less cortisol than controls, a response that was not reversed upon treatment with the GR antagonist RU486. 5-HT-stimulated cortisol release was significantly lower from both crowded and cortisol-implanted toadfish interrenal cells compared to controls. Incubation with either a 5-HT(4) or a 5-HT(2) receptor agonist significantly stimulated cortisol secretion; however, incubation with 8-OH-DPAT did not, suggesting that the 5-HT(1A) receptor is not a mediator of cortisol release at the level of the interrenal cells. Combined, these results explain in part the disconnect between brain 5-HT(1A) levels and cortisol secretion.

Localization and role of serotonin in the adrenal gland of Podarcis sicula (Reptilia, Lacertidae)

The occurrence of serotonin (5-hydroxytryptamine; 5-HT) in the chromaffin cells of Podarcis sicula adrenal gland was demonstrated by immunocytochemical techniques: ABC and immunogold methods. At LM and EM levels, antiserum against 5-HT revealed serotonin immunoreactivity prevalently in noradrenalin (NA) cells, on and around secretory vesicles; adrenalin (A) cells appeared scarcely stained. The role of serotonin in the regulation of adrenal gland activity was studied in vivo using LM and EM techniques coupled to a specific radioimmunoassay for adrenocorticotropic hormone (ACTH) and corticosterone. 5-HT (0.7 mg/100 g body wt)/day for 4 days increased ACTH and corticosterone release; at LM and EM level clear signs of stimulation in the steroidogenic tissue were observed, as evidenced by the variations of lipid/cytoplasm ratio. In the chromaffin tissue, LM observations evidenced a variation of the numeric NA/A cell ratio; at EM level, chromaffin tissue showed intermediate cells with A, NA, and very clear granules with granular elements. The occurrence of these cells might be the result of a process of resynthesis following serotonin-stimulated catecholamine release. These data suggested that serotonin might be involved in the modulation of Podarcis pituitary-adrenal axis, and act as a paracrine factor to modulate corticosteroid production.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Chromaffin-adrenocortical cell interactions: effects of chromaffin cell activation in adrenal cell cocultures

Although the adrenal cortex and medulla are both involved in the maintenance of homeostasis and stress response, the functional importance of intra-adrenal interactions remains unclear. When primary cocultures of frog (Rana pipiens) adrenocortical and chromaffin cells were used, selective chromaffin cell activation dramatically affected both chromaffin and adrenocortical cells. Depolarization with 50 microm veratridine enhanced chromaffin cell neuronal phenotype, contacts with adrenocortical cells, and secretion of norepinephrine, epinephrine, and serotonin. Time-lapse video microscopy recorded the rapid establishment of growth cones on the activated chromaffin cell neurites, neurite branching, and outgrowth toward adrenocortical cells. Simultaneously, adrenocortical cells migrated toward chromaffin cells. Following chromaffin cell activation, adrenocortical cell Fos protein expression and corticosteroid secretion were increased, indicating that chromaffin cell modulation of adrenocortical cells is at the transcriptional level. These results provide evidence that intra-adrenal interactions affect cellular differentiation and modulate steroidogenesis. Furthermore, this suggests that the activity-related plasticity of chromaffin and adrenocortical cells is developmentally and physiologically important.

Role of 5-HT in the regulation of the brain-pituitary-adrenal axis: effects of 5-HT on adrenocortical cells

Serotonin (5-HT) plays a pivotal role in the regulation of the brain-pituitary-adrenal axis. In particular, 5-HT has been shown to control the activity of hypothalamic CRF neurons and pituitary corticotrope cells through activation of 5-HT1A and (or) 5-HT2A/2C receptor subtypes. 5-HT, acting through 5-HT2 receptors, can also trigger the renin-angiotensin system by stimulating renin secretion and consequently can enhance aldosterone production. At the adrenal level, 5-HT produced locally stimulates the secretory activity of adrenocortical cells through a paracrine mode of communication. The presence of 5-HT in the adrenal gland has been demonstrated immunohistochemically and biochemically in various species. In the frog, rat, and pig adrenal gland, 5-HT is synthesized by chromaffin cells, while in the mouse adrenal cortex, 5-HT is contained in nerve fibers. In man, 5-HT is present in perivascular mast cells. In vivo and in vitro studies have shown that 5-HT stimulates corticosteroid secretion in various species (including human). The type of receptor involved in the mechanism of action of 5-HT differs between the various species. In frogs and humans, the stimulatory effect of 5-HT on adrenocortical cells is mediated through a 5-HT4 receptor subtype positively coupled to adenylyl cyclase and calcium influx. In the rat, the effect of 5-HT on aldosterone secretion is mediated via activation of 5-HT7 receptors. Clinical studies indicate that 5-HT4 receptor agonists stimulate aldosterone secretion in healthy volunteers and in patients with corticotropic insufficiency and primary hyperaldosteronism. Local serotonergic control of corticosteroid production may be involved in the physiological control of the activity of the adrenal cortex as well as in the pathophysiology of cortisol and aldosterone disorders.Key words: HPA axis, renin-angiotensin system, adrenal gland, corticosteroid secretion, serotonergic receptors.

Frog chromaffin and adrenocortical cell co-cultures: a model for the study of medullary control of corticosteroidogenesis

Phylogenetic, physiological and morphological evidence indicates that interactions between chromaffin and adrenocortical cells are involved in the differentiation and maintenance of function of both cell types. Chromaffin-adrenocortical interaction has become recognized as an important component of adrenocortical regulation; however, the mechanisms by which chromaffin cells modulate adrenocortical function are not well understood. To study directly chromaffin-adrenocortical cellular interactions, we developed primary frog (Rana pipiens) adrenal co-cultures. In these co-cultures, chromaffin cells extend processes that project towards or onto adrenocortical cells, mimicking their organization in vivo and indicating a potential for interaction between the two cell types. Cell survival and differentiation were optimized using a combination of NGF, FGF and histamine to enhance neurite outgrowth and fetal calf serum plus 10(-10) M ACTH to maintain steroidogenesis. Characterization of the cells by immunocytochemistry and histochemistry showed that chromaffin cells maintain expression of catecholamine biosynthetic enzymes and that adrenocortical cells maintain expression of steroidogenic enzymes. Furthermore, chromaffin cells release catecholamines upon stimulation with carbamylcholine or potassium while adrenocortical cells sustain a basal secretion rate of aldosterone and corticosterone that is augmented 10-40-fold by 0.1 nM to 10 nM ACTH. We therefore propose that these co-cultures serve as a useful model system to study the cellular and molecular mechanisms by which chromaffin cells modulate adrenocortical cell function.

Hormonal responses to the administration of m-chlorophenylpiperazine in patients with seasonal affective disorder and controls

We report on the plasma cortisol and prolactin responses to the serotonergic agonist m-CPP (0.1 mg/kg) in 10 patients with winter seasonal affective disorder (SAD) and 10 controls during the winter, in both untreated and bright light-treated conditions; and on 8 other SAD patients and 8 other controls during the summer. Following m-CPP infusion, untreated patients had exaggerated prolactin (p < .05) and cortisol (p < .05) responses compared to controls. Light treatment significantly reduced responses of both hormones to m-CPP (prolactin: p < .01; cortisol: p < .01). When untreated winter subjects and summer subjects were compared, cortisol, but not prolactin responses to m-CPP were found to be higher in patients than in controls during the winter, and lower in patients than in controls during the summer (diagnosis by season: p < .05). These results are consistent with those of our previous report on the behavioral responses to m-CPP in the same patients and suggest an abnormality in serotonergic function in untreated SAD patients in winter, which is normalized following treatment with light therapy and naturally during the summer.

Involvement of the cytoskeleton in the mechanism of action of endothelin on frog adrenocortical cells

In a previous report, we have shown that endothelin-1 (ET-1) is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. In the present study, we examine the possible involvement of cytoskeletal elements in the mechanism of action of ET-1 on corticosteroid secretion from frog adrenal gland. The microfilament disrupting agent cytochalasin B (5 x 10(-5) M) induced a reversible inhibition of the spontaneous secretion of corticosteroid and blocked the response of adrenocortical cells to ET-1 (5 x 10(-9) M). In contrast, the antimicrotubular agent vinblastine (10(-5) M) and the intermediate filament inhibitor beta-beta' iminodipropionitrile (10(-3) M) had virtually no effect on both spontaneous and endothelin-induced steroidogenesis. Taken together, these results indicate that, in the frog adrenal gland, the integrity of the microfilament network is required for the corticotropic activity of ET-1 whereas microtubules and intermediate filaments are apparently not involved in the mechanism of action of ET-1.

Physiopharmacological interactions between stress hormones and central serotonergic systems

The present review tries to delineate some mechanisms through which the sympathetic nervous system (SNS) and the hypothalamo-pituitary-adrenal (HPA) interact with central serotonergic systems. The recent progress in 5-hydroxytryptamine (5-HT) receptor pharmacology has helped to define the means by which central serotonergic activity may alter the respective activities of the SNS (sympathetic nerves and adrenomedulla) and of the HPA axis. These pharmacological findings have also helped to characterize the differential effects of central 5-HT upon different branches of the SNS and the numerous sites at which 5-HT exerts stimulatory influences upon the HPA axis. Although relevant to stress-related neuroendocrinology, the extent to which these interactions are involved in the antidepressant/anxiolytic properties of some serotonergic agents still remains to be clarified. Beside these findings, there is also abundant evidence for a tight control of central serotonergic systems by stress hormones. Activation of the SNS increases, by numerous means, central availability of tryptophan, whereas glucocorticoids exert differential actions upon the intra- and the extraneuronal regulation of 5-HT function. Actually, a significant number of these mechanisms is involved in the maintenance of homeostasis during stressful events, thereby conferring to these mechanisms a key role in adaptation processes.

In vitro study of the effect of adenosine on frog adrenocortical cells

Previous reports have shown that adenosine in rat inhibits both spontaneous and ACTH-induced release of corticosteroids through activation of adenosine A1 receptors. In the present study, we have investigated the possible effect of adenosine in the secretion of corticosteroids in amphibians using a perfusion technique for frog adrenocortical slices. Infusion of adenosine, at concentrations ranging from 10(-7) to 10(-4) M, had no effect on the basal output of corticosterone and aldosterone by frog interrenal cells. Similarly, adenosine did not affect the response of frog adrenocortical slices to ACTH, vasoactive intestinal peptide, or angiotensin II. The stable adenosine A1 receptor agonist N6-phenylisopropyl adenosine (PIA) was also totally devoid of effect on the spontaneous or ACTH-induced release of corticosteroids. These results show that in amphibians, adenosine does not modulate adrenal steroidogenesis.

Serotonin-induced stimulation of cortisol secretion from human adrenocortical tissue is mediated through activation of a serotonin4 receptor subtype

The occurrence of serotonin in the human adrenal gland was demonstrated both by immuno-histochemical and biochemical approaches. Using specific polyclonal antibodies to serotonin, the presence of numerous immunoreactive cells was revealed by means of the peroxidase-antiperoxidase technique. These cells exhibited the morphological characteristics of mast cells. Combination of high performance liquid chromatography and electrochemical detection showed the presence of substantial amounts of both serotonin and its metabolite 5-hydroxyindolacetic acid in adrenocortical extracts. The role of serotonin in the regulation of steroidogenesis from human adrenocortical slices was studied in vitro using a perifusion system technique coupled to a specific radioimmunoassay for cortisol. Graded doses of serotonin (from 10(-8) M to 3 x 10(-7) M) increased cortisol production in a dose-dependent manner. Prolonged exposure of adrenal fragments to serotonin (10(-7) M) induced a biphasic response, i.e. a rapid and transient increase in cortisol secretion followed by a plateau phase, suggesting the existence of a desensitization phenomenon. The stimulatory effect of serotonin (10(-7) M) was not altered during infusion of the serotonin1 and/or serotonin2 receptor antagonists methysergide (10(-6) M) and ketanserin (10(-6) M), respectively. In contrast, ICS 205 930 (10(-6) M), a non-selective serotonin3/serotonin4 antagonist, totally abolished the response of adrenal slices to serotonin (10(-7) M). The benzamide derivative zacopride, considered as a serotonin4 agonist, induced a robust stimulation of cortisol secretion. In addition, the corticotropic effects of serotonin (10(-7) M) and zacopride (10(-6) M) were not additive. Incubation of adrenocortical fragments with zacopride (10(-6) M) or serotonin (10(-6) M) caused a significant increase in cAMP formation. Taken together, these data suggest that serotonin, locally released by intra-adrenal mast-like cells, may act as a paracrine factor to stimulate cortisol secretion in man. Our results also indicate that serotonin-induced corticosteroid production is mediated through activation of a serotonin4 receptor subtype positively coupled to adenylate cyclase.

Interactions between vasotocin and other corticotropic factors on the frog adrenal gland

The adrenocortical cells of the amphibian interrenal (adrenal) gland are controlled by multiple factors including neuropeptides and classical neurotransmitters. In particular, it has recently been shown that vasotocin (AVT), the amphibian counterpart of vasopressin, is a potent stimulator of frog corticosteroidogenesis. In the present study, we have investigated the possible interactions between AVT and other regulatory factors on frog interrenal tissue. When AVT (10(-9) M) and serotonin (10(-6) M) were infused together, a strict addition of the individual effects was observed. Similar results were obtained with concomitant infusion of AVT and vasoactive intestinal peptide or AVT and ACTH. In contrast, when AVT (10(-9) M) and acetylcholine (5 x 10(-5) M) were added together, the increase in corticosteroid secretion was less than additive. Dopamine induced a significant reduction of AVT-evoked stimulation of corticosterone production. These results indicate that regulatory peptides or classical neurotransmitters which participate in the control of adrenal steroidogenesis may interact on their target cell to modulate the activity of their congeners.

Serotonin synthesis in adrenochromaffin cells

The inter-renal (adrenal) gland of amphibians is composed of chromaffin and steroidogenic cells which can interact through a paracrine mode of communication. We have previously shown that serotonin is present in secretory granules of frog adrenochromaffin cells; concurrently, we have demonstrated that serotonin is a potent stimulator of corticosterone and aldosterone secretion by adrenocortical cells. The aim of the present study was to determine the origin of the amine contained in frog chromaffin cells. Using 3H-labelled tryptophan as a precursor, we observed the formation of substantial amounts of serotonin and its metabolite 5-hydroxyindoleacetic acid by frog inter-renal slices. Newly synthesized serotonin was secreted into the incubation medium and the release process was enhanced by depolarizing concentrations of KCl. Fluoxetine, and inhibitor of serotonin uptake, caused an increase of 3H-labelled serotonin in the incubation medium, suggesting that the indoleamine was taken up again by adrenal chromaffin cells. The capacity of the frog inter-renal gland to synthesize serotonin was also demonstrated by incubating inter-renal slices with non-labelled tryptophan or 5-hydroxytryptophan. In these conditions, we observed that the rate of synthesis was higher when 5-hydroxytryptophan was used as a a precursor, rather than tryptophan. Taken together, these results indicate that chromaffin cells, which have the capacity for synthesizing and releasing serotonin, behave like authentic serotonergic paraneurons. As far as is known, these data provide the first evidence for the occurrence of tryptophan-5-hydroxylase activity within the adrenal gland.

Benzamide derivatives provide evidence for the involvement of a 5-HT4 receptor type in the mechanism of action of serotonin in frog adrenocortical cells

We have previously shown that serotonin (5-HT) is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells and we have demonstrated that the action of 5-HT is not mediated by the classical 5-HT receptor subtypes i.e. 5-HT1, 5-HT2 and 5-HT3. Recently, a non-classical 5-HT receptor (termed 5-HT4) has been characterized using 4-amino-5-chloro-2-methoxy-benzamide derivatives as serotonergic agonists. In the present report, we have investigated the possible involvement of the 5-HT4 receptor subtype in the mechanism of action of 5-HT on steroid secretion. Increasing concentrations of benzamide derivatives (zacopride, cisapride and BRL 24924) gave rise to a dose-related stimulation of corticosteroid production, zacopride being the most potent compound of this series to enhance steroidogenesis. Prolonged administration (230 min) of zacopride induced a rapid increase in corticosterone and aldosterone output followed by a gradual decline of corticosteroid secretion. During prolonged exposure of adrenal tissue to zacopride (10(-5) M), the corticotropic activity of 5-HT (10(-6) M) was totally abolished. The stimulatory effects of 5-HT and zacopride were abolished by the non-selective 5-HT3 antagonist ICS 205 930. In contrast methysergide, a 5-HT1 receptor antagonist, and MDL 72222, a selective 5-HT3 antagonist did not block zacopride-induced corticosteroid secretion. Both 5-HT and zacopride induced a dose-related increase in cAMP production by frog adrenal slices. Taken together, these results indicate that the stimulatory effect of 5-HT on frog adrenocortical tissue is mediated by activation of a 5-HT4 receptor subtype positively coupled to adenylate cyclase.

Structure-activity relationships of monomeric and dimeric synthetic ACTH fragments in perifused frog adrenal slices

The effect of synthetic monomeric and dimeric ACTH fragments on spontaneous and ACTH(1-39)-evoked steroidogenesis in frog interrenal tissue was studied in vitro. Infusion of ACTH fragment 11-24 (10(-6) M) or its dimeric conjugates, attached either by their N-terminal, Glu(11-24)2, or their C-terminal amino acid, (11-24)2Lys, had no effect on the spontaneous release of corticosteroids. The monomer ACTH(11-24) and the dimer Glu(11-24)2 were also totally devoid of effect on the steroidogenic response to ACTH(1-39) (10(-9)M). In contrast, the (11-24)2Lys conjugate (10(-6)M) significantly decreased ACTH-induced stimulation of corticosterone and aldosterone (-63 and -62%, respectively). The dimeric conjugate of the fragment ACTH(7-24), linked through the C-terminal ends, (7-24)2Lys (10(-6)M), was also completely devoid of effect on basal steroidogenesis but caused a marked decrease of ACTH-evoked corticosterone and aldosterone release (-72 and -80%, respectively). Conversely, infusion of the dimer (1-24)2Lys gave rise to a dose-related stimulation of corticosterone and aldosterone release. The time-course of the steroidogenic response to the dimer was similar to that of ACTH(1-24). The 1-24 conjugate was 70 times less potent than the monomers ACTH(1-24) and ACTH(1-39). These results suggest that amphibian adrenocortical cells contain only one class of ACTH receptor which recognizes the 11-24 domain of ACTH with an affinity which depends on the presence of a strong potentiator segment, located at the N-terminus end of ACTH(1-39). Since the ACTH-dimers are thought to induce cross-linking of the receptors, our results suggest that aggregation of ACTH receptors causes a down-regulation of the receptors.

Mechanism of action of serotonin on frog adrenal cortex

The mechanism of action of serotonin (5-HT) on frog adrenal cortex has been investigated in vitro using the perifusion system technique. The direct effect of 5-HT on corticosteroid secreting cells was demonstrated, using enzymatically dispersed adrenocortical cells. Melatonin and 5-HTP appeared to be less potent than 5-HT to enhance corticosteroid secretion. In contrast Trp and 5-HIAA were totally devoid of effect on steroid secretion. To investigate the type of receptor involved in the stimulatory effect of 5-HT on adrenocortical cells, adrenal slices were stimulated with 5-HT in absence or presence of various antagonists. We observed that classical antagonists of 5-HT1, 5-HT2 and 5-HT3 type receptors failed to block 5-HT-induced corticosteroid secretion in our model. These results show that 5-HT exerts a direct effect on corticosteroid-secreting cells. Our data also indicates that the type of receptor involved in the action of 5-HT in frog adrenal cortex differs from mammalian 5-HT receptors.

Dopamine inhibits corticosteroid secretion in frog adrenocortical cells: evidence for the involvement of prostaglandins in the mechanism of action of dopamine

We have investigated the possible involvement of arachidonic acid metabolites in dopamine-induced inhibition of adrenocortical steroidogenesis. Administration of dopamine (5 x 10(-5) M) for 20 min to perifused frog adrenal slices caused a marked reduction of the release of both prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha, the stable metabolite of prostacyclin (PGI2). Dopamine also induced a significant inhibition of corticosterone and aldosterone secretion. A lag period of 20 min was observed between inhibition of prostanoid and corticosteroid releases. Prolonged dopamine infusion did not prevent the stimulatory effect of PGE1, PGE2 or arachidonic acid on corticosteroid secretion. These observations indicate that activation of dopaminergic receptors in adrenocortical cells is linked to an inhibition of arachidonic acid metabolism. Our data also suggest that the inhibitory effect of dopamine occurs at a step preceding arachidonic acid formation.

Immunohistochemical and biochemical evidence for the presence of serotonin in amphibian adrenal chromaffin cells

The presence of serotonin (5-HT) in chromaffin cells of the frog adrenal (inter-renal) gland has been demonstrated both by immunocytochemical and biochemical techniques. Using antisera against 5-HT and tyrosine hydroxylase (TH) on consecutive sections, we found by means of the indirect immunofluorescence technique that a majority of chromaffin cells were also immunopositive for 5-HT. When antibodies to 5-HT and phenylethanolamine-N-methyltransferase (PNMT) were applied on consecutive sections, 5-HT-like immunoreactivity was observed in almost all epinephrine-producing cells which represented about 90% of the total chromaffin cells. No 5-HT-containing fibres could be detected. At the ultrastructural level, using a pre-embedding procedure associated with gold-silver intensification of the immunoperoxidase reaction, 5-HT-immunoreactivity was visualized in secretory vesicles essentially located in the periphery of epinephrine cells. Combination of high performance liquid chromatography and electrochemical detection showed the presence of both 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in frog adrenal extracts. Transection of the splanchnic nerve enhanced 5-HT immunoreactivity and augmented the amount of 5-HT in adrenal extracts. Taken together, these results indicate that epinephrine-producing cells of the frog adrenal contain significant amounts of serotonin. The observation of the storage of 5-HT in secretory vesicles of epinephrine cells suggests that serotonin may be released with catecholamines under stress conditions.

Neuronal and paracrine regulation of adrenal steroidogenesis: interactions between acetylcholine, serotonin and vasoactive intestinal peptide (VIP) on corticosteroid production by frog interrenal tissue

The adrenocortical cells of frog interrenal (adrenal) tissue are controlled by multiple factors. Recently, we have shown that corticosteroidogenesis is stimulated by acetylcholine released from splanchnic nerve terminals as well as by serotonin and vasoactive intestinal peptide (VIP) which are both contained in chromaffin cells. Since these 3 putative neuroregulators are known to interact with each other on various target organs, we have investigated possible coordinate actions of acetylcholine, serotonin and VIP on adrenal steroid production, using a perifusion system technique for frog interrenal tissue. Simultaneous infusion of submaximal doses of VIP (10(-5) M) and acetylcholine (5 X 10(-5) M) induced stimulations of corticosteroids (corticosterone and aldosterone) which were strictly additive. When VIP (10(-5) M) and serotonin (5 X 10(-6) M) were infused together, a potentiation of the individual responses was observed. In contrast, concomitant infusion of acetylcholine (5 X 10(-5) M) and serotonin (5 X 10(-6) M) caused a total blockage of the stimulatory effect of serotonin. Muscarine (10(-5) M) caused a similar blockade of the response of adrenocortical cells to serotonin while nicotine (5 X 10(-5) M) did not alter the stimulatory effect of serotonin. The inhibitory effect of acetylcholine on serotonin-induced steroidogenesis was antagonized by atropine (10(-5) M). Thus, acetylcholine appears to block the corticotropic action of serotonin by interacting with typical muscarinic receptors. Taken together our results indicate that 3 of the neuroregulators which participate in the control of adrenal steroidogenesis, namely acetylcholine, serotonin and VIP, may interact on their target cell to modulate the activity of their congeners.(ABSTRACT TRUNCATED AT 250 WORDS)