Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

ECRG4 expression in normal rat tissues: expression study and literature review

The Esophageal Cancer Related Gene 4 (ECRG4) is a highly conserved tumour suppressor gene encoding various peptides (augurin, CΔ16 augurin, ecilin, argilin, CΔ16 argilin) which can be processed and secreted. In the present work, we examined ECRG4 expression and location in a wide range of rat organs and reviewed the available literature. ECRG4 mRNA was identified in all examined tissues by quantitative PCR (qPCR). ECRG4 immunoreaction was mainly cytoplasmic, and was detected in heart and skeletal muscles, smooth muscle cells showing only weak reactions. In the digestive system, ECRG4 immunostaining was stronger in the esophageal epithelium, bases of gastric glands, hepatocytes and pancreatic acinar epithelium. In the lymphatic system, immunoreactive cells were detectable in the thymus cortex, lymph node medulla and splenic red pulp. In the central and peripheral nervous systems, different neuronal groups showed different reaction intensities. In the endocrine system, ECRG4 immunoreaction was detected in the hypothalamic paraventricular and supraoptic nuclei, hypophysis, thyroid and parathyroid glands, adrenal zona glomerularis and medulla and Leydig cells, as well as in follicular and luteal cells of the ovary. In the literature, ECRG4 has been reported to inhibit cell proliferation and increase apoptosis in various cell types. It is down-regulated, frequently due to hypermethylation, in esophageal, prostate, breast and colon cancers, together with glioma (oncosuppressor function), although it is up-regulated in papillary thyroid cancer (oncogenic role). ECRG4 expression is also higher in non-proliferating cells of the lymphatic system. In conclusion, our identification of ECRG4 in many structures suggests the involvement of ECRG4 in the tumorigenesis of other organs and also the need for further research. In addition, on the basis of the location of ECRG4 in neurons and endocrine cells and the fact that it can be secreted, its role as a neurotransmitter/neuromodulator and endocrine factor must be examined in depth in the future.

Immune-neuroendocrine integration at the adrenal gland: cytokine control of the adrenomedullary transcriptome

The bovine chromaffin cell represents an ideal model for the study of cell signaling to gene expression by first messengers. An abundance of GPCR, ionotropic, and growth factor receptors are expressed on these cells, and they can be obtained and studied as an abundant highly enriched cell population; importantly, this is true of no other postmitotic neuroendocrine or neuronal cell type. Chromaffin cells have now been shown to bear receptors for cytokines whose expression in the circulation is highly elevated in inflammation, including tumor necrosis factor, interferon, interleukin-1, and interleukin-6. The use of bovine-specific microarrays, and various biochemical measurements in this highly homogenous cell preparation reveals unique cohorts of distinct genes regulated by cytokines in chromaffin cells, via signaling pathways that are in some cases uniquely neuroendocrine. The transcriptomic signatures of cytokine signaling in chromaffin cells suggest that the adrenal medulla may integrate neuronal, hormonal, and immune signaling during inflammation, through induction of paracrine factors that signal to both adrenal cortex and sensory afferents of the adrenal gland, and autocrine factors, which determine the duration and type of paracrine secretory signaling that occurs in either acute or chronic inflammatory conditions.

Spexin expression in normal rat tissues

Spexin is a highly conserved peptide which was recently identified through the bioinformatics approach. Immunohistochemical analysis of its expression has not yet been performed. Thus, in this study, we examined spexin location in a wide range of rat organs by both RT-PCR and IHC. RT-PCR identified spexin mRNA in all tissues examined. Spexin immunoreaction was mainly cytoplasmic. Spexin was immunohistochemically detected, although with different staining intensities, in epithelia and glands of skin and respiratory, digestive, urinary, and reproductive systems. Smooth muscle cells showed weak immunostaining, and connective tissue was negative. In the central nervous system, neuronal groups showed different intensities for reaction product. Immunoreaction was also found in ganglionic cells of both trigeminal and superior cervical ganglia and in photoreceptor, inner nuclear, and ganglionic layers of the retina. In the endocrine system, spexin immunoreaction was detected in the hypothalamic paraventricular and supraoptic nuclei; adenohypophysis, thyroid, and parathyroid glands; adrenal cortex and medulla (mainly ganglionic cells); Leydig cells; and thecal, luteal, and interstitial cells of the ovary. Because of its widespread expression, spexin is probably involved in many different physiological functions; in particular, location of spexin in neurons and endocrine cells suggests its roles as neurotransmitter/neuromodulator and endocrine factor.

Expression of the spexin gene in the rat adrenal gland and evidences suggesting that spexin inhibits adrenocortical cell proliferation

Spexin (SPX, also called NPQ) is a recently identified, highly conserved peptide which is processed and secreted. We analysed the SPX gene and its protein product in the rat adrenal gland to ascertain whether SPX is involved in the regulation of corticosteroid secretion of and growth of adrenocortical cells. In adult rat adrenal glands the highest levels of SPX mRNA were present in the glomerulosa (ZG) and fasciculate/reticularis (ZF/R) zones. High SPX gene expression levels were found in freshly isolated adult rat ZG and ZF/R cells. In cultured adrenocortical cells the levels of SPX mRNA were lower than in freshly isolated cells. SPX mRNA expression levels were found to be 2-3 times higher during days 90-540 of postnatal development than found during days 2-45. Prolonged ACTH administration lowered and dexamethasone increased adrenal SPX mRNA levels in vivo. Adrenal enucleation produced a significant linear increase in SPX mRNA levels, with the highest value occurring at day 8 after surgery, with control values taken on day 30 after enucleation. Immunohistochemistry revealed SPX-like immunoreactivity in the entire cortex of the adult male rat and in enucleation-induced regenerating cortex. A concentration of 10-6M SPX peptide stimulated basal aldosterone secretion by freshly isolated ZG. In prolonged exposure of adrenocortical cell primary cultures to SPX (10-6M) resulted in a small increase in corticosterone secretion and a notable decrease in BrdU incorporation. The results suggest the direct involvement of SPX in the regulation of adrenocortical cell proliferation; however, the mechanism of action remains unknown.

Endogenous Ligands of PACAP/VIP Receptors in the Autocrine–Paracrine Regulation of the Adrenal Gland

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the main endogenous ligands of a class of G protein-coupled receptors (Rs). Three subtypes of PACAP/VIP Rs have been identified and named PAC(1)-Rs, VPAC(1)-Rs, and VPAC(2)-Rs. The PAC(1)-R almost exclusively binds PACAP, while the other two subtypes bind with about equal efficiency VIP and PACAP. VIP, PACAP, and their receptors are widely distributed in the body tissues, including the adrenal gland. VIP and PACAP are synthesized in adrenomedullary chromaffin cells, and are released in the adrenal cortex and medulla by VIPergic and PACAPergic nerve fibers. PAC(1)-Rs are almost exclusively present in the adrenal medulla, while VPAC(1)-Rs and VPAC(2)-Rs are expressed in both the adrenal cortex and medulla. Evidence indicates that VIP and PACAP, acting via VPAC(1)-Rs and VPAC(2)-Rs coupled to adenylate cyclase (AC)- and phospholipase C (PLC)-dependent cascades, stimulate aldosterone secretion from zona glomerulosa (ZG) cells. There is also proof that they can also enhance aldosterone secretion indirectly, by eliciting the release from medullary chromaffin cells of catecholamines and adrenocorticotropic hormone (ACTH), which in turn may act on the cortical cells in a paracrine manner. The involvement of VIP and PACAP in the regulation of glucocorticoid secretion from inner adrenocortical cells is doubtful and surely of minor relevance. VIP and PACAP stimulate the synthesis and release of adrenomedullary catecholamines, and all three subtypes of PACAP/VIP Rs mediate this effect, PAC(1)-Rs being coupled to AC, VPAC(1)-Rs to both AC and PLC, and VPAC(2)-Rs only to PLC. A privotal role in the catecholamine secretagogue action of VIP and PACAP is played by Ca(2+). VIP and PACAP may also modulate the growth of the adrenal cortex and medulla. The concentrations attained by VIP and PACAP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their adrenal content is consistent with a local autocrine-paracrine mechanism of action.

Irregular and frequent cortisol secretory episodes with preserved diurnal rhythmicity in primary adrenal Cushing's syndrome

To evaluate the pathophysiology of altered cortisol secretion in patients with primary adrenal hypercortisolism, cortisol secretion was investigated in 12 patients, seven with a unilateral adenoma and five with ACTH-independent macronodular adrenal hyperplasia compared with age- and gender-matched controls and with patients with pituitary-dependent hypercortisolism. Pulsatile secretion was increased 2-fold (P = 0.04), attributable to increased event frequency (P = 0.002). All patients showed a significant diurnal rhythm with a delay in phase shift of 3 h (P = 0.01). Approximate entropy ratio, a feedback-sensitive measure, was increased compared with controls (P = 0.00003) but similar to that of pituitary-dependent hypercortisolism (P = 0.77), denoting loss of autoregulation. Cortisol burst-mass tended to be smaller in patients with ACTH-independent macronodular adrenal hyperplasia than in unilateral adenoma (P = 0.06). In conclusion, increased cortisol secretion in patients with primary adrenal Cushing's syndrome is caused by amplified pulsatile secretion via event frequency modulation. We speculate that partial preservation of secretory regularity and diurnal rhythmicity point to incomplete autonomy of these tumors.

Dependence of fetal hairs and sebaceous glands on fetal adrenal cortex and possible control from adrenal medulla

Human fetal adrenal development is characterized by rapid growth, high steroidogenic activity, and a distinct morphology, including a unique cortical compartment known as the fetal zone. For most of gestation, the predominant fetal zone accounts for 80-90% of the cortical volume and is the primary site of growth and steroidogenesis, producing 100-200 mg/day of the androgenic steroid, dehydroepiandrosterone sulfate (DHEA-S). The physiological role of this zone during intrauterine life is not well understood. While the glands appear to be capable of DHEA-S synthesis early in gestation (8-10 weeks), we noticed that this event precedes the differentiation of hairs and sebaceous glands. Hairs begin to develop between 9 and 12 weeks and sebaceous glands between 13 and 15 weeks of gestation. Sebaceous glands form an oily secretion - sebum that mixes with desquamated epidermal cells to form vernix caseosa. Vernix caseosa protects the developing skin from constant exposure to amniotic fluid, and hairs helps to hold the vernix caseosa on the skin. We suggest therefore that the human fetal adrenal cortex produces DHEA-S beginning at around 8-10 weeks of gestation in sufficient quantities to influence the growth of hairs and sebaceous glands. Soon after birth, the fetal zone atrophies, and adrenal androgen production decreases to minimal levels. As a consequence, in concordance with the rapid decrease in adrenal androgen levels and in consistent with our hypothesis, fetal hairs are shed and sebaceous glands shrink to small structures. The mechanism that regulates fetal adrenal androgen production is a key unanswered problem in human adrenal biology. Since there exists a close relationship between epinephrine and DHEA-S levels during adrenarche which shows modulatory interactions between adrenal androgen production and adrenomedullary function, we suggest again that adrenomedullary function might play a role in the control of fetal adrenal androgen secretion.

Adrenal neuropeptides: regulation and interaction with ACTH and other adrenal regulators

It is now well accepted that both the cortex and medulla of the mammalian adrenal gland receive a rich innervation. Many different transmitter substances have been identified in nerves supplying both cortex and medulla and, as well as catecholamines, a wide range of neuropeptides has been found in the adrenal gland. There have been several studies on the affects of age, sodium intake, stress, ACTH, and splanchnic nerve activity on the regulation of adrenal neuropeptide content. There is evidence that the abundance of each of these peptides is actively regulated. Although there have been many studies addressing the individual actions of various neurotransmitters on steroid secretion, adrenal blood flow, and adrenal growth, few have attempted to determine the nature of any interaction between neurotransmitters and the classical adrenal stimulants. There are, however, some significant interactions, particularly in the regulation of zona glomerulosa function. This review necessarily focuses on vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), as these are the most abundant transmitter peptides in the adrenal gland and the majority of studies have investigated their regulation and actions. However, substance P, calcitonin gene-related peptide (CGRP), neurotensin, and the enkephalins are included where appropriate. Finally, it has been suggested that certain neurotransmitters, particularly VIP, may interact with classical hormone receptors in the adrenal, notably the ACTH receptor. This review attempts to evaluate our current state of knowledge in each of these areas.

Acute ethanol treatment increases level of progesterone in ovariectomized rats

To determine whether an increased level of progesterone in adult female rats after acute ethanol treatment, described previously in our study, is the result of activation of adrenal glands, we analyzed adrenal cortex morphologically and measured serum levels of corticosterone and progesterone in ovariectomized rats. In addition, a possible involvement of the opioid system in an observed phenomenon was tested. Adult female Wistar rats were ovariectomized, and 3 weeks after surgery they were treated intraperitoneally with (a) ethanol (4 g/kg), (b) naltrexone (5 mg/kg), followed by ethanol (4 g/kg) 45 min later, and (c) naltrexone (5 mg/kg), followed by saline 45 min later. Untreated and saline-injected rats were used as controls. The animals were killed 0.5 h after ethanol administration. Morphometric analysis was carried out on paraffin sections of adrenal glands, stained with hematoxylin-eosin, and the following parameters were determined: absolute volume of the zona glomerulosa, the zona fasciculata, and the zona reticularis; numerical density, volume, and the mean diameter of adrenocortical cells and of their nuclei; and mean diameter and length of capillaries. The results showed that acute ethanol treatment significantly increased absolute volume of the zona fasciculata and length of its capillaries but did not alter other stereological parameters. Also, serum levels of corticosterone and progesterone were enhanced. Pretreatment with naltrexone had no effect on ethanol-induced changes. These findings are consistent with our previous hypothesis that an ethanol-induced increase of the progesterone level in adult female rats originates from the adrenal cortex.

The hypothalamic-pituitary-adrenal response to critical illness

The maintenance of life depends on the capacity of the organism to sustain its equilibrium via allostasis'-the ability to achieve stability through change. Life-threatening disease induces acute adaptive responses specific to the stimulus and generalized responses when the disturbances are prolonged. These changes are associated with increased activity of the hypothalamic-pituitary-adrenal axis and may have survival value in preparing the body for fight or flight'. There is a shift towards an increase in glucocorticoid production and away from mineralocorticoid and androgen production, as well as an increase in the biological effects of glucocorticoids through an increased cortisol free fraction and an increased glucocorticoid receptor sensitivity. During the prolonged phase, there is a dissociation between high plasma cortisol and low adrenocorticotropin hormone levels, suggesting non-adrenocorticotropin hormone-mediated mechanisms for the regulation of the adrenal cortex. This hypercortisolism is in contrast to the very low dehydroepiandrosterone sulphate level, indicating an imbalance between the immunostimulatory and immunosuppressive adrenocortical hormones. The question is whether the total serum cortisol concentration represents sufficient glucocorticoid biological activity during the prolonged phase of critical illness.

Regulation of rat adrenal vasoactive intestinal peptide content: effects of adrenocorticotropic hormone treatment and changes in dietary sodium intake

Vasoactive intestinal peptide (VIP) is well established as a paracrine regulator of adrenal function. It is present in nerves supplying the adrenal cortex, although previous studies have found that the amount of VIP in the outer zones of the rat adrenal is not affected by ligating the splanchnic nerve supplying the adrenal gland. The present studies were designed to investigate the mechanisms involved in regulating the VIP content of the rat adrenal gland. This study examined the effects of changes in electrolyte balance and adrenocorticotropic hormone (ACTH) administration on the adrenal content of VIP as measured by radioimmunoassay. Rats on a low sodium diet had a significantly increased capsular/zona glomerulosa immunoreactive VIP (irVIP) level, while rats on a high sodium diet had suppressed levels relative to controls. Changes in dietary sodium did not affect inner zone/medullary VIP content. Administration of ACTH caused a decrease in irVIP levels in the capsular/zona glomerulosa portion of the adrenal gland but had no effect on the inner zone/medulla. Analysis of mRNA encoding VIP revealed a large increase in expression of VIP in the sodium-deplete group compared with the control, with no change in VIP expression in the sodium-loaded group. ACTH treatment was found to significantly decrease VIP mRNA levels in the capsular portion. Neither ACTH treatment nor changes in sodium intake affected inner zones/medullary VIP message. These data suggest that VIP in the capsule and zona glomerulosa region of the adrenal cortex is regulated in response to the physiological status of the animal, with changes in capsular/zona glomerulosa VIP correlating with changes in zona glomerulosa function.

Influence of morphine treatment in pregnant rats on the mineralocorticoid activity of the adrenals in their neonates

Exposure of pregnant rats to morphine, from day 11 to day 18 of gestation, was previously reported to induce both an adrenal atrophy and hypoactivity of the glucocorticoid function in newborns at term, but did not affect, in vitro, the responsiveness of those glands to adrenocorticotrophin hormone (ACTH) concerning corticosterone release. Moreover, these effects were mediated by maternal hormones from the adrenal glands. In the present work, we investigated the effects of a prenatal morphine exposure on the mineralocorticoid activity of the adrenals in neonates. The first aim of the present study was to determine in these newborns 1) the adrenal and plasma aldosterone concentrations at birth time and during the early postnatal period 2) the plasma levels of Na+ and K+ at birth time, 3) the in vitro responsiveness of the newborn adrenals to angiotensin II (A(II)) and ACTH. The second aim of our study was to investigate the mineralocorticoid activity of the adrenals in newborns from adrenalectomized mothers treated with morphine during gestation. According to present data morphine given to intact mothers induced in newborns a severe adrenal atrophy but increased adrenal aldosterone content and plasma aldosterone level. However, prenatal morphine was unable to affect significantly Na+/K+ ratio in both mothers and newborns. In vitro, the adrenals of neonates from morphine-treated mothers were unresponsive to An and ACTH for promoting aldosterone release; in contrast, aldosterone secretion was significantly stimulated by high potassium levels (55 mEq). Maternal adrenalectomy performed one day before the beginning of morphine treatment prevented morphine-induced adrenal atrophy but was unable to affect significantly the adrenal mineralocorticoid function of the offspring. Such data suggest that a prenatal morphine exposure stimulated both aldosterone synthesis and release in neonates. However, this basal hyperfunction did not appear to be coupled with an enhanced adrenal responsivity to AII or ACTH. Prenatal morphine-induced hyperactivity of the mineralocorticoid function of the newborn adrenals, which drastically contrast with hypoactivity of the glucocorticoid one, was independent of adrenal factors from maternal origin.

Regulation of rat adrenal neuropeptide Y (NPY) content: effects of ACTH, dexamethasone and hypophysectomy

While the presence of neuropeptide Y (NPY) in the adrenal cortex is well established, little is known about its regulation. In the present study the involvement of the pituitary gland in the regulation of rat adrenal NPY content was investigated. Rats were subjected to one of the following treatments: hypophysectomy, sham operation, ACTH, the synthetic glucocorticoid, dexamethasone, dexamethasone plus ACTH, or saline control. The immunoreactive NPY (irNPY) content of both capsule/zona glomerulosa and inner zone/medulla fractions were estimated by radioimmunoassay. Treatment with ACTH caused a significant decrease in both the capsular/zona glomerulosa and the inner zone/medulla irNPY content compared with controls, while hypophysectomy resulted in a significant increase in adrenal irNPY. Dexamethasone treatment caused a significant increase in capsular irNPY, which was reversed by simultaneous administration of ACTH. In the medulla, however, dexamethasone treatment significantly decreased irNPY content. These results suggest that there is differential regulation of adrenal irNPY content, with irNPY in the zona glomerulosa regulated directly by ACTH, while the irNPY content of the inner zones/medulla is regulated by glucocorticoids.

Regulation of the biosynthesis of large dense-core vesicles in chromaffin cells and neurons

1. The proteins of large dense-core vesicles (LDV) in neuroendocrine tissues are well characterized. Secretory components comprise chromogranins and neuropeptides. Intrinsic membrane proteins include cytochrome b-561, transporters, SV2, synaptotagmin, and synaptobrevin. 2. The effects of stimulation and of second messengers on the biosynthesis of LDV have been studied in detail. 3. Regulation of biosynthesis is complex. The cell can adapt to prolonged stimulation either by producing vesicles of normal size filled with a higher quantum of secretory peptides or by forming larger vesicles. In addition, some components, e.g., enzymes, can be upregulated specifically.

Neuroendocrine effects on adrenal hormone secretion in carp (Cyprinus carpio)

The responses of interrenal and chromaffin tissues of carp to acetylcholine (Ach) and its agonists/antagonists were studied in an in vitro perifusion system of head kidney. There was a dose-dependent release of epinephrine and norepinephrine to Ach between 0.01 and 100 mM added for 15 min to the incubation medium. Cortisol secretion was also stimulated, but the response peaked at 1.0 mM Ach and was attenuated with 10 or 100 mM Ach. The maximal release occurred about 30 min after addition of the transmitter. Nicotine stimulated the catecholamines, but had no effect on cortisol, while carbamylcholine, a nicotinic agonist, increased both the catecholamines and cortisol. Muscarine increased cortisol secretion, but affected catecholamines only at higher doses. In contrast, pilocarpine, a muscarinic agonist, stimulated catecholamines more than cortisol. Atropine was not antagonistic, rather it increased the secretion of catecholamines in a dose-dependent manner, and inhibited the release of cortisol. It is concluded that both tissues are influenced by the autonomic nervous system, with the sympathetic system acting on chromaffin cells and the parasympathetic system acting on interrenal cells. However, the nerve supply cannot clearly be defined by agonists or antagonists as in mammals. There is evidence for paracrine effects, e.g., catecholamines inhibit cortisol release and cortisol influences catecholamine secretion.

Innervation of the adrenal cortex, its physiological relevance, with primary focus on the noradrenergic transmission

The current knowledge of the catecholaminergic innervation of the mammalian adrenal cortex is summarized, and macro- and microscopic neuromorphology, including the central nervous system connections of the adrenal cortex, is briefly discussed. Morphological and functional data on the catecholaminergic (i.e., noradrenergic) innervation of the adrenal cortex are reviewed. Experimental data suggest that in addition to the regulation of adrenal blood flow, the noradrenergic innervation has a primary influence on zona glomerulosa cells possibly via beta 1 adrenergic and dopaminergic receptors (DA2 subtype via inhibiting T-type Ca2+ channels) It is concluded that the local, modulatory effect of noradrenergic nerve fibres, terminating in the close vicinity of the zona glomerulosa cells, on the systemic renin-angiotensin-aldosterone and other peptide cascade may be influenced by neuropeptides, particularly neuropeptide Y and vasoactive intestinal peptide.

The role of endothelins in the paracrine control of the secretion and growth of the adrenal cortex

Endothelins (ETs) are a family of vasoactive peptides (ET-1, ET-2, and ET-3) mainly secreted by vascular endothelium and widely distributed in the various body systems, where they play major autocrine/paracrine regulatory functions, acting via two subtypes of receptors (ETA and ETB): Adrenal cortex synthesizes and releases ETS and expresses both ETA and ETB. Zona glomerulosa possesses both ETA and ETB, whereas zona fasciculata/reticularis is almost exclusively provided with ETB. ETS exert a strong mineralocorticoid and a less intense glucocorticoid secretagogue action, mainly via ETB receptors. ETS also appear to enhance the growth and steroidogenic capacity of zona glomerulosa and to stimulate its proliferative activity. This trophic action of ETS is likely to be mediated mainly by ETA receptors. The intraadrenal release of ETS undergoes a multiple regulation, with the rise in blood flow rate and the local release of nitric oxide being the main stimulatory factors. Data are also available that indicate that ETS may also have a role in the pathophysiology of primary aldosteronism caused by adrenal adenomas and carcinomas.

Role of adrenomedullin and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Adrenomedullin (ADM) is a hypotensive peptide, originally isolated from human pheochromocytomas, and then found to be widely distributed in the various body systems. ADM derives from preproadrenomedullin, a 185-amino acid residue prohormone, containing at its N-terminal a 20-amino acid sequence, named proadrenomedullin N-terminal 20 peptide (PAMP). ADM and PAMP immunoreactivities have been detected in the hypothalamo-pituitary-adrenal (HPA) axis of humans, rats, and pigs. Adrenal glands possess binding sites for both ADM and PAMP, the former being mainly of the subtype 1 of calcitonin gene-related peptide (CGRP) receptors. ADM exerts a direct inhibitory action on angiotensin II- or potassium-stimulated aldosterone secretion of zona glomerulosa cells. This effect is mediated by the CGRP1 receptor and its mechanism probably involves the blockade of Ca2+ influx. In contrast, ADM enhances aldosterone production by in situ perfused rat adrenals and human adrenal slices (containing medullary chromaffin cells), again through the activation of CGRP1 receptors. This aldosterone secretagogue effect of ADM is blocked by the beta-adrenoceptor antagonist l-alprenolol, thereby suggesting that it is indirectly mediated by the release of catecholamines by chromaffin cells. The effects of ADM on adrenal glucocorticoid release are doubtful and probably mediated by the increase in adrenal blood flow rate and the inhibition of ACTH release by pituitary corticotropes. The concentrations reached by ADM and PAMP in the blood rule out the possibility that they act on the HPA axis as circulating hormones. Conversely, their content in both adrenal and hypothalamo-pituitary complex is consistent with a paracrine mechanism of action, which may play a potentially important role in the regulation of fluid and electrolyte homeostasis.

Sympathetic effects on the steroidogenesis and proliferation of adrenocortical cells in vitro

Recent evidence supports the hypothesis that sympathetic neurons play a significant role in the regulation of adrenocortical cell proliferation and steroidogenesis. Co-cultures of rat adrenocortical and sympathetic ganglion cells have been established to study sympatho-adrenal interactions. In these studies we have compared differentiation, growth and secretion of adrenocortical cells grown in co-culture with those grown alone. Adrenocortical cells were identified using 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) histochemistry or immunocytochemistry; sympathetic neurons were identified using immunocytochemical localization of tyrosine hydroxylase. The sympathetic neurons usually form clusters of 3-10 cells, and extend neurites to adrenocortical cells. Adrenocortical cells continue to proliferate, express 3 beta HSD and sequester lipid droplets. In the co-cultures, the adrenocortical cells are smaller, form larger clusters and show denser 3 beta HSD staining than the adrenocortical cells alone. The presence of the sympathetic neurons enhances adrenocortical cell proliferation as shown by a 2 fold increase in the number of 3 beta HSD(+) cells as well as increased BrdU incorporation after 48 hrs. Steroidogenesis appeared to be enhanced in the presence of sympathetic neurons as demonstrated by 3 beta HSD(+) staining and a 2-fold greater corticosterone and aldosterone secretion. However, when secretion is expressed per number of adrenocortical cells, the rates are comparable, indicating that secretion rate per cell remains unaltered by the presence of neurons. The effects of sympathetic neuron activation on adrenocortical cells remain to be determined.

Effects of substance P and its antagonist spantide on corticosterone secretion and cytosolic free calcium concentration of dispersed zona fasciculata-reticularis cells of the rat adrenal cortex

Substance P (SP) did not change basal corticosterone (B) secretion of dispersed zona fasciculata-reticularis cells of the rat adrenal cortex. Conversely, spantide II (SPA), an antagonist of SP receptors, at a concentration 10(-7)/10(-6) M markedly raised it, and the effect was annulled by equimolar concentrations of SP. Both SP and SPA (10(-6) M) increased cytosolic free calcium concentration in our cell preparations; however, the response to SP was immediate, while that to SPA showed a lag-period of 4-5 min. SP concentration-dependently (from 10(-8) M to 10(-5) M) partially inhibited maximally ACTH (10(-8) M)-induced stimulation of B secretion of dispersed cells, and unexpectedly a similar effect was observed after SPA exposure. In light of these findings, the conclusion is drawn that SP, under basal conditions, does not exert a direct modulatory action of B secretion of rat adrenocortical cells. However, the possibility remains to be explored that SP may play a role in quenching, via a receptor-independent mechanism, the exceedingly high glucocorticoid responses to ACTH of rat adrenocortical cells.

Adrenomedullin and calcitonin gene-related peptide inhibit aldosterone secretion in rats, acting via a common receptor

Adrenomedullin (ADM) and calcitonin gene-related peptide (CGRP) did not affect either basal or ACTH-stimulated secretion of a1dosterone and corticosterone by dispersed rat capsular and inner adrenocortical cells, respectively. However, both peptides strongly depressed angiotensin-II (ANG- II)-stimulated a1dosterone production by capsular cells, the minimal effective concentration was 10(-7) M. The inhibitory effect of both ADM and CGRP was reversed by CGRP8-37, a specific CGRP1 receptor antagonist; a complete reversal was obtained with a CGRP8-37 concentration of 10(-6) M. Our findings indicate that ADM and CGRP specifically interfere with the intracellular mechanisms transducing the secretagogue signal of ANG-II, and suggest that the ADM effect is mediated by CGRP receptors

Adrenomedullin stimulates steroid secretion by the isolated perfused rat adrenal gland in situ: comparison with calcitonin gene-related peptide effects

Adrenomedullin (ADM), a vasodilatatory peptide contained in adrenal medulla, was found to induce a dose-dependent increase in aldosterone (ALDO) and corticosterone (B) release by the in situ perfused rat adrenal gland, along with a rise in the flow rate of the perfusion medium. The minimal effective dose for ALDO response was three and two orders of magnitude less than those able to evoke B and medium flow rate responses. Calcitonin gene-related peptide (CGRP), another vasodilatatory peptide contained in adrenal medulla and showing a slight homology in its amino acid sequence with ADM, elicited similar effects. CGRP (8-37), a specific antagonist of CGRP1 receptors, annulled all the effects of both ADM and CGRP, whereas l-alprenolol, a beta-adrenoceptor antagonist, partially reversed only ALDO response to the peptides. In light of these findings the following conclusions are drawn: i) ADM and CGRP stimulate rat adrenals in vivo to release B by raising blood flow rate; ii) ADM and CGRP enhance ALDO secretion via an indirect mechanism probably requiring the release of catecholamines by medullary chromaffin cells; and iii) the effects of ADM and CGRP on the rat adrenal gland are mediated by a common receptor of the CGRP1 subtype.