Neurotensin (NT) and bombesin (BM)-like peptides are known to be involved in the regulation of the rat hypothalamo-pituitary-adrenal axis. By using selective NT- and BM-receptor antagonists (NT-A and BM-A, respectively) we investigated whether endogenous NT and BM-like peptides play a role in the control of rat adrenal secretion and growth during enucleation-induced regeneration. At day 5 of regeneration, NT-A did not affect the plasma concentrations of aldosteronc (PAC) and corticosterone (PBC), but at day 8, it raised both PAC and PBC over the respective baseline value; the simultaneous administration of NT abolished this effect of NT-A. BM-A did not alter PAC and PBC at day 5 of regeneration, while at day 8 it enhanced PBC, an effect reversed by BM. NT-A did not alter mitotic index, and BM-A lowered it at both day 5 and day 8 of regeneration, an effect suppressed by the simultaneous administration of BM. Collectively, these findings allow us to draw the following conclusions: 1) endogenous NT and BM-like peptides influence adrenocortical regeneration in rats; 2) NT exerts a tonic inhibitory action on both aldosterone and corticosterone secretion, without affecting cell-proliferation rate; and 3) BM-like peptides exert a tonic suppressive effect on corticosterone production, coupled with a clear-cut stimulating effect on cell proliferation.

Gastric inhibitory polypeptide (GIP) is a 42-amino acid peptide, belonging to the VIP-secretin-glucagon superfamily, some members of this group are able to regulate adrenocortical function. GIP-receptor mRNA has been detected in the rat adrenal cortex, but investigations on the effect of GIP on steroid-hormone secretion in this species are lacking. Hence, we have investigated the distribution of GIP binding sites in the rat adrenal gland and the effect of their activation in vivo and in vitro. Autoradiography evidenced abundant [125I]GIP binding sites exclusively in the inner adrenocortical layers, and the computer-assisted densitometric analysis of autoradiograms demonstrated that binding was displaced by cold GIP, but not by either ACTH or the selective ACTH-receptor antagonist corticotropin-inhibiting peptide (CIP). The intraperitoneal (IP) injection of GIP dose-dependently raised corticosterone, but not aldosterone plasma concentration: the maximal effective dose (10 nmol/rat) elicited a twofold increase. GIP did not affect aldosterone and cyclic-AMP release by dispersed zona glomerulosa cells. In contrast, GIP enhanced basal corticosterone secretion and cyclic-AMP release by dispersed inner adrenocortical cells in a concentration-dependent manner, and the maximal effective concentration (10(-7) M) evoked 1.5- and 2.4-fold rises in corticosterone and cyclic-AMP production, respectively. GIP (10(-7) M) did not display any additive or potentiating effect on corticosterone and cyclic-AMP responses to submaximal or maximal effective concentrations of ACTH. The corticosterone secretagogue action of 10(-7) M GIP was abolished by the protein kinase A (PKA) inhibitor H-89 (10(-5)M), and unaffected by CIP (10(-6)M). Collectively, these findings indicate that GIP exerts a moderate but statistically significant stimulatory effect on basal glucocorticoid secretion in rats, acting through specific receptors coupled with the adenylate cyclase/PKA-dependent signaling pathway.

Arginine-vasopressin (AVP) and atrial natriuretic peptide (ANP) are contained in adrenal medulla and are thought to control aldosterone secretion by the zona glomerulosa in a paracrine manner. Endothelin-1 (ET-1), a potent aldosterone secretagogue, can enhance AVP and ANP release by rat hypothalamo-neurohypophyseal axis and atrial cardiocytes respectively. Hence, we have investigated the effects of ET-I on AVP and ANP release by rat adrenal medulla fragments in vitro. Radioimmunoassay showed that ET-1 enhanced AVP-immunoreactivity (ir) release in a concentration-dependent manner, minimal and maximal effective concentrations being 10(-9) and 10(-7) M, respectively. The effect of ET-1 on ANP-ir release was less intense and significant only at a peptide concentration of 10(-8)/10(-7) M. The secretagogue effects of ET-1 (10(-7) M) were annulled by ETA-receptor antagonist BQ-123 (5 x 10(-7) M), and unaffected by the ETB-receptor antagonist BQ-788 ET-1 (10(-7) M) evoked a marked rise in aldosterone secretion of rat adrenal slices. This effect of ET-1 was slightly but significantly counteracted by an antagonist of AVP, but not of ANP receptors. Collectively, these findings allow us to conclude that: (1) ET-1 stimulates rat adrenal medulla secretion of both AVP and ANP, exclusively acting via the ETA-receptor subtype; and (2) the ETA receptor-mediated release of AVP, but not of ANP may play a role in the aldosterone secretagogue effect of ET-1. Med Sci Res 27:163-165 (C) 1999 Lippincott Williams & Wilkins.

Frozen sections of normal adrenal glands, obtained from patients undergoing unilateral nephrectomy for kidney cancer, were labeled in vitro with human [125I]ADM(1-52). Autoradiography showed the presence of abundant ADM binding sites in the zona glomerulosa (ZG) and the outermost portion of the zona fasciculata, which were completely displaced by the addition of an excess of cold ADM(1-52). Calcitonin gene-related peptide (CGRP) and the non-selective ligand of the CGRP-receptor subtypes 1 and 2 CGRP(8-37) eliminated [125I]ADM(1-52) binding in the ZG, while the selective ligand of CGRP receptor subtype 2 [Cys(acm)2,7]-CGRP and CGRP(1-8) were ineffective. These findings confirm the presence of ADM binding sites in the human ZG, and provide the first morphological evidence that ADM and CGRP interact with a common receptor of the CGRP1 subtype.

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) are two hypotensive peptides, which are able to inhibit agonist-stimulated aldosterone secretion from adrenal zona glomerulosa. In this study we examined the effects of these two peptides on the aldosterone response of dispersed human adrenocortical cells to maximal effective concentrations of their main agonists. ADM (10(-7) M) and PAMP (10(-8) M) did not affect either basal or ACTH-stimulated aldosterone secretion, but they counteract ed the secretory response to both 10(-9) M angiotensin-II (ANG-II) (partial inhibition) and 10 mM K+ (complete inhibition). The Ca2+ ionophore A23187 (10(-5) M) partially reversed the inhibitory effect of both peptides on aldosterone response to ANG-II, and abolished that on aldosterone response to K+. Collectively these findings provide indirect evidence that the mechanism underlying the aldosterone anti-secretagogue action of ADM and PAMP may involve the impairment of the agonist-induced rise in the cytosolic Ca2+ concentration, and especially of Ca2+ influx.

Pancreatic polypeptide (PP) concentration-dependently raised basal corticosterone and cyclic-AMP production of dispersed rat zona fasciculata/reticularis adrenocortical cells, maximal effective concentration being 10(-7) M. 10(-7) M PP also significantly enhanced submaximally (10[-12]/10[-11] M), but not maximally (10[-9]/10[-8] M) ACTH-stimulated corticosterone and cyclic-AMP release. Corticosterone responses to PP were abolished by the specific protein kinase A (PKA) antagonist H-89 (10[-5] M). The selective ACTH-receptor antagonist corticotropin-inhibiting peptide (10[-6] M) annulled corticosterone response to 10(-9) M ACTH, but not to 10(-7) M PP. Collectively, our present findings indicate that PP stimulates glucocorticoid secretion of rat adrenal glands, acting through specific receptors coupled, like those of ACTH, with the adenylate cyclase/PKA-dependent signaling pathway.

Frozen sections of normal adrenal glands, obtained from patients undergoing unilateral nephrectomy for kidney cancer, were labeled in vitro with human [125I]ADM(1-52). Autoradiography and quantitative densitometry showed the presence of abundant ADM(1-52) binding sites in both zona glomerulosa (ZG) and capsular vessels, which were displaced with about the same efficiency by cold ADM(1-52) and rat ADM(1-50). The selective calcitonin gene-related peptide type 1 (CGRPI) ligand CGRP(8-37) eliminated, although less efficiently than ADMs, [125I]ADM(1-52) binding in the ZG, but not in the capsular vessels. These findings suggest the existence of different receptor subtypes for ADM in the human adrenal cortex. The CGRP(8-37)-sensitive receptors located in the ZG may mediate the well-known inhibitory effect of ADM on aldosterone secretion, while the CGRP(8-37)-insensitive receptors present in the capsular vessel may be involved in the ADM-induced rise in adrenal blood flow.

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) are two hypotensive peptides, contained in adrenal medulla, which are able to inhibit aldosterone secretion from zona glomerulosa. In this study we have compared the effects of the two peptides on the production of post-pregnenolone steroids by dispersed rat zona glomerulosa cells. ADM and PAMP did not alter basal steroid secretion. Conversely, they inhibited angiotensin-II (10(-9) M)-stimulated 18-hydroxy-11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone and aldosterone production, without affecting progesterone and 11-deoxycorticosterone secretion. PAMP was significantly more effective than ADM, their minimal effective concentrations being 10(-10) M and 10(-8)-10(-7) M, respectively. ADM, but not PAMP markedly lowered either basal and agonist-enhanced release of 11-dehydrocorticosterone. Collectively, these findings allow us to draw the following conclusions: (i) ADM and PAMP electively inhibit 11 beta-hydroxylase and aldosterone synthase, PAMP being probably to be considered the proadrenomedullin-derived physiological inhibitor of mineralocorticoid secretion in rats; and (ii) ADM, but not PAMP, also exerts a clear-cut inhibitory action on 11 beta-hydroxysteroid dehydrogenase, the enzyme that converts corticosterone to its inactive form.

Teaching of gross Anatomy, the oldest between medical sciences, today suffers the lack of cadavers for notomization, therefore this subject is more theoretical than practical in medical school. The computer techniques could be very useful in this field. Is it possible nowadays to get a software of Virtual Anatomy? The answer is yes. We present in this work a review of the state-of-art of these techniques mainly based on data acquired by computer tomography (CT) or magnetic resonance imaging (MRI) from human. Serial slices obtained from imaging (CT or MRI) can be reconstructed using computers in order to generate a realistic view of the surface of an anatomical object.

Endothelins (ETs) and their receptor subtypes A and B (ETA and ETB) are expressed in the various components of the mammalian hypothalamo-pituitary-adrenal (HPA) axis, but their involvement in the functional regulation of HPA is controversial. To gain insight into this topic, we have investigated the effects of ET-1 and/or the specific antagonists of ETA and ETB receptors (BQ-123 and BQ-788, respectively) on the plasma concentrations of ACTH, corticosterone and aldosterone of non-stressed (control) and ether- or cold-stressed rats. The study of the effects of the administration of the two ET-receptor antagonists alone could provide informations about the possible action of endogenous ETs on the HPA axis. Exogenous ET-1 increased ACTH, corticosterone and aldosterone blood levels in control rats, as well as evoked a sizable enhancement of the HPA axis response to ether stress and a marked depression of the response to cold stress. BQ-123 and BQ-788 did not prevent the stimulatory effect of exogenous ET-1 in control rats, but when administered alone, raised the plasma concentrations of ACTH, corticosterone and aldosterone. Both ET-receptor antagonists magnified the HPA axis response to ether and cold stresses, but their effect was not counteracted by exogenous ET-1. Although very difficult to interpret, our present findings allow us to conclude that endogenous ETs play a role in the maintenance of the basal activity of rat HPA axis acting through ETA and ETB receptor subtypes, which are partially insensitive to BQ-123 and BQ-788. Conversely, the involvement of ETs in the modulation of the HPA axis responses to various stresses is very doubtful.

Pneumadin (PNM), a decapeptide isolated from mammalian lungs, has previously been found not to affect corticosterone release from dispersed rat adrenocortical cells, but to enhance it in vivo, probably by stimulating the pituitary release of ACTH and arginine-vasopressin (AVP). The present study shows that the administration of PNM markedly raised corticosterone production by rat adrenal slices containing medullary chromaffin cells, and that this effect was prevented by antagonists of both ACTH and AVP receptors. The conclusion is drawn that PNM elicits the intra-adrenal release of ACTH and AVP, which in turn stimulates glucocorticoid secretion by adrenocortical cells in a paracrine manner.

The localization of endothelin (ET) receptor subtypes ET(A) and ET(B) in the rat kidney corpuscles, and which receptor subtype mediates the in vitro inhibitory effect of ET-1 on renin secretion have been investigated. The autoradiographic examination of the selective displacement of I-125-ET-1, I-125-ET-3 and I-125-BQ-3020 (an ET(B) agonist) by BQ-123 or BQ-788 (specific antagonists of ET(A) and ET(B), respectively) indicated that kidney corpuscles possess both ET(A) and ET(B) receptors, whereas their vascular peduncles are almost exclusively provided with ET(A). ET-1 inhibited in a concentration-dependent manner both basal and isoproterenol-stimulated renin secretion from rat kidney cortex slices. BQ-123 concentration-dependently reversed this effect of ET-1, while BQ-788 was ineffective. ET-3 evoked a very moderate inhibition of basal, but not isoproterenol-stimulated, renin release, while BQ-3020 was ineffective. BQ-123 per se did not evoke any change in the kidney renin secretion. These findings suggest that in the rat ETs inhibit renin secretion acting via ET(A) receptors probably located on the juxtaglomerular cells of the kidney corpuscles.

Endothelins (ET) are a family of vasoconstrictor peptides, secreted by vascular endothelium, which act through two main subtypes of receptors: ETA and ETB. ET-1 is known to stimulate aldosterone (ALDO) secretion by adrenal zona glomerulosa (ZG), and in vitro its effect was recently found to be exclusively mediated by ETB receptors. In this study the involvement of ETA and ETB in the mediation of the in vivo acute ALDO secretagogue action of ET-1 was investigated by the use of their selective antagonists BQ-123 and BQ-788, respectively. The bolus intraperitoneal administration of ET-1 dose-dependently raised both basal and angiotensin II (ANG II)-enhanced plasma ALDO concentration (PAC) in rats. Both antagonists counteracted the stimulatory effect of ET-1 on basal PAC, and when administered together completely annulled it. Conversely, only BQ-788 reversed the effect of ET-1 on ANG II-enhanced PAC. ET-1 increased systolic blood pressure (BP) in normal rats, but not in animals simultaneously administered ANG II. The hypertensive effect of ET-1 was completely abolished by BQ-123, and not affected by BQ-788. In light of these findings the following conclusions can be drawn: (i) the in vivo ALDO secretagogue action of ET-1 is mediated by both ETA and ETB, this latter subtype of ET receptors playing a major role; and (ii) the mechanism whereby ETA participates in this in vivo effect of ET-1 is indirect, and probably connected with the ET-1-induced rise in BP and adrenal blood flow.

The acute bolus intraperitoneal (i.p.) administration of pancreatic polypeptide (PP) dose-dependently enhanced the plasma concentration of corticosterone (PBC) in hypophysectomized/ACTH replaced rats, but not that of aldosterone. Minimal and maximal effective doses were 10(-12) and 10(-10) mol/rat, respectively, and maximal PBC increase occurred between 60 and 120 min after PP injection. Insulin (1 U/kg, i.p.) evoked a net decrease in the blood glucose concentration, and marked rises in the plasma levels of PP and PBC, that attained their maximum at 60 and 120 min, respectively. The effects of insulin were annulled by the simultaneous injection of 0.5 mg/kg atropine. The effects of 1 U/kg insulin and 10(-10) mol/rat PP on PBC were not additive; atropine did not affect PBC response to PP or PP plus insulin, though annulling that to insulin alone. Taken together these findings suggest that PP plays a physiologic role in the rat as modulator of the adrenal response to the insulin-induced hypoglycemic stress.

Arginine-vasopressin (AVP) markedly increased basal aldosterone (ALDO) secretion by dispersed zona-glomerulosa (ZG) cells, and its effect was selectively reversed by V1-receptor antagonists (AVP-A1). Corticosterone (B) production by dispersed zona fasciculata (ZF) cells was not affected. The bolus intraperitoneal (i.p.) administration of AVP acutely raised the plasma concentrations of both ALDO and B in normal rats, but only that of ALDO in bilaterally adrenalectomized animals bearing regenerated adrenocortical autotransplants, which are deprived of medullary chromaffin cells. Accordingly, AVP raised ALDO and B secretions by adrenal slices (including both cortical and medullary tissues), and only ALDO production by autotransplant quarters. The B response of adrenal slices to AVP was blocked by alpha-helical-CRH and corticotropin-inhibiting peptide (two competitive inhibitors of CRH and ACTH, respectively), but not by 1-alprenolol (a beta-adrenoreceptor antagonist); ALDO response was not affected by any of these antagonists. A 7-day i.p. infusion with AVP increased the volume of ZG cells and ZG-like cells of autotransplants, as well as their basal and maximally angiotensin-II-stimulated ALDO secretory capacity; it also raised the volume, and basal and maximally ACTH-stimulated B secretory capacity of ZF cells, but it did not affect ZF-like cells of autotransplants. The simultaneous administration of AVP-A1 annulled all these effects of AVP. When infused alone, AVP-A1 caused a marked atrophy of ZG cells, coupled with a net drop in their steroidogenic capacity; however, AVP-A1 infusion did not change the morphology and function of either ZF cells or ZG-like and ZF-like cells of autotransplants. Taken together,, our findings allow us to draw the following conclusions: (i) AVP plays an important physiological role in the maintenance and stimulation of ZG growth and mineralocorticoid secretory activity in rats, the source of endogenous AVP exerting adrenoglomerulotropic action probably being adrenal chromaffin cells; and (ii) AVP indirectly stimulates the growth and glucocorticoid secretory activity of rat ZF cells, by activating intramedullary CRH/ACTH system; however, the physiological relevance of this effect of AVP appears to be doubtful.

The in vitro effect of vasoactive intestinal polypeptide (VIP) on mineralo- and glucocorticoid secretion was investigated in the rat by using adrenal slices, containing zona-medullaris cells, and fragments of adrenocortical autotransplants regenerated from gland capsular-tissue implants, which are completely deprived of chromaffin cells. VIP dose-dependently enhanced basal aldosterone (ALDO) and corticosterone (B) secretions by both kinds of tissue preparations. The maximal effect was observed at a concentration 10(-8) M, but the rise was about 3-fold higher in the case of ALDO secretion by adrenal slices. Corticotropin-inhibiting peptide (CIP), a competitive inhibitor of ACTH, and l-alprenolol (AL), a beta-adrenoceptor antagonist, did not affect basal steroidogenesis of both preparations. CIP (10(-6) M) completely annulled the maximal stimulatory effect of VIP on B production by adrenal slices and ALDO and B secretion by autotransplant quarters, but it did only reduce (by about 50%) that on ALDO production by adrenal slices. AL (10(-7) M) caused a 73% decrease in VIP (10(-8) M)-stimulated ALDO secretion by adrenal slices and when added with CIP (10(-6) M) completely annulled it. In light of these findings, it seems reasonable to suggest that VIP exerts a secretagogue effect on rat adrenal steroidogenesis by a two-fold mechanism: (i) non-specific stimulation of both mineralo- and glucocorticoid secretion by activation of a population of ACTH receptors, and (ii) specific stimulation of mineralocorticoid secretion through the enhancement of catecholamine release by chromaffin cells.

A 7-day subcutaneous infusion with the AVP antagonist [Deamino-Pen1, Val4, D-Arg8]-vasopressin (AVP-A; 3 nmol.kg-1 x min-1) significantly lowered plasma aldosterone concentration in rats, without affecting the plasma levels of ACTH and corticosterone. Prolonged AVP-A treatment caused a marked atrophy of adrenal zona glomerulosa (ZG) and its parenchymal cells, without inducing any significant change in zona fasciculata morphology. Isolated ZG cells from AVP-A-infused rats evidenced a notable decrease in both their basal and maximally-stimulated aldosterone production. The simultaneous infusion of rats with AVP (3 nmol.kg-1 x min-1) completely reversed all these effects of AVP-A. These findings suggest that endogenous AVP may be specifically involved in the maintenance of the growth and steroidogenic capacity of rat adrenal ZG. Moreover, they seem to indicate that under basal conditions the pituitary-adrenal-glucocorticoid axis is independent of AVP release.

The bolus ip. injection of rat calcitonin gene-related peptide (CGRP) (5 pm. kg-1) significantly lowered plasma aldosterone concentration (PAC) in rats, despite a mild rise in plasma renin activity. Natremia, kalaemia and the blood levels of ACTH or corticosterone were not affected. Similar results were obtained after prolonged (5 days) sc. infusion of rats with CGRP (1 pm. kg-1. h-1). Moreover, CGRP infusion caused a notable atrophy of the zona glomerulosa (ZG) and its parenchymal cells, as well as a clearcut reduction in the surge of PAC evoked by a bolus injection of a high dose of angiotensin-II (100 micrograms. kg-1). From these results it is suggested that CGRP exerts an inhibitory effect on the growth and secretory activity of ZG in rats.

The bolus ip. administration of a SRIF antagonist (SRIF-A) (60 nM/rat) significantly increased renin activity (PRA) and plasma aldosterone concentration (PAC) in rats, without affecting natremia, kalaemia and the blood levels of ACTH or corticosterone. SRIF-A also raised PAC in rats whose renin-angiotensin system had been pharmacologically interrupted by combined captopril/angiotensin-II infusion and in which PRA was very low. The ip. injection of an equimolar dose of SRIF completely reversed these effects of SRIF-A, but the administration of SRIF alone did not affect either PRA or PAC. Taken together, these data would suggest that, in the rat, endogenous SRIF exerts, under basal conditions, a two-fold maximum tonic inhibitory effect on both renin release by kidneys and aldosterone secretion by zona glomerulosa cells.

A bolus IP injection of interleukin-1β (IL-1β) (8 μg·kg−1) increased blood pressure and PRA without affecting plasma aldosterone (ALDO) concentration. IL-1β strongly attenuated angiotensin-II (ANG-II, 10−8 M)-stimulated ALDO secretion by both isolated zona glomerulosa (ZG) cells and capsular strips. These findings suggest that IL-1β exerts a twofold opposite action on the main components of the rat renin-angiotensin-aldosterone system: simultaneous stimulation of renin release by kidneys and inhibition of the stimulatory effect of ANG-II on ALDO production. At the highest concentrations (10−6/10−5 M), IL-1β was found to lower also basal ALDO output by isolated ZG cells, but not by capsular strips. However, in the presence of saralasin 10−8 M (a competitive inhibitor of ANG-II) and captopril 10−8 M (an angiotensin-I-converting enzyme inhibitor), IL-1β significantly reduced basal ALDO yield of capsular strips. These last results would suggest that IL-1β could also similarly affect the intraadrenal renin-angiotensin system, which seems to be involved in the local regulation of ZG secretory activity.