The role of neuropeptides in the regulation of adrenal zona fasciculata/reticularis function. Effects of vasoactive intestinal polypeptide, substance P, neuropeptide Y, Met- and Leu-enkephalin and neurotensin on corticosterone secretion in the intact perfused rat adrenal gland in situ

Chronic psychosocial stress results in sensitization of the HPA axis to acute heterotypic stressors despite a reduction of adrenal in vitro ACTH responsiveness

Although chronic psychosocial stress is often accompanied by changes in basal hypothalamo-pituitary-adrenal (HPA) axis activity, it is vital for a chronically-stressed organism to mount adequate glucocorticoid (GC) responses when exposed to acute challenges. The main aim of the present study was to test whether this is true or not for the chronic subordinate colony housing (CSC, 19 days) paradigm, an established and clinically relevant mouse model of chronic psychosocial stress. As shown previously, CSC mice are characterized by unaffected morning and decreased evening plasma corticosterone (CORT) levels despite enlarged adrenals, suggesting a maladaptive breakdown of adrenal functioning. Plasma CORT levels, determined by repeated blood sampling via jugular vein catheters, as well as relative right adrenal CORT content were increased in CSC compared with single-housed control (SHC) mice in response to acute elevated platform (EPF, 5min) exposure. However, in vitro stimulation of adrenal explants with physiological and pharmacological doses of ACTH revealed an attenuated responsiveness of both the left and right adrenal glands following CSC, despite mRNA and/or protein expression of melanocortin 2 receptor (Mc2r), Mc2r accessory protein (MRAP), and key enzymes of steroidogenesis were not down-regulated. Taken together, we show that chronic psychosocial stressor exposure impairs in vitro ACTH responsiveness of both the left and right adrenal glands, whereas it increases adrenal responsiveness to an acute heterotypic stressor in vivo. This suggests that an additional factor present during acute stressor exposure in vivo rescues left and right adrenal ACTH sensitivity, or itself acts as CORT secretagogue in chronically stressed CSC mice.

Control of hormonal stress reactivity by the endogenous opioid system

Regulations of hormonal stress responses entail the initiation, amplitude and termination of the reaction, as well as its integration with other stress response systems. This study investigates the role of endogenous opioids in the regulation and integration of behavioral, thermal and hormonal stress responses, as these neuromodulators and their receptors are expressed in limbic structures responsible for stress responses. For this purpose, we subjected mice with selective deletion of beta-endorphin, enkephalin or dynorphin to the zero-maze test, a mildly stressful situation, and registered behaviors and stress hormone levels. Behavioral stress reactivity was assessed using zero-maze, light-dark and startle-reactivity paradigms. Animals lacking enkephalin displayed increased anxiety-related behavioral responses in each three, dynorphin knockouts in two models, whereas the responses of beta-endorphin knockouts indicated lower anxiety level in the zero-maze test. All knockout strains showed marked changes in hormonal stress reactivity. Increase in ACTH level after zero-maze test situation, unlike in wild type animals, failed to reach the level of significance in Penk1(-/-) and Pdyn(-/-) mice. Corticosterone plasma levels rapidly increased in all strains, with a lower peak response in knockouts. In wild-type and beta-endorphin-deficient mice, corticosterone levels returned to baseline within 60min after stress exposure. In contrast, mice lacking dynorphin and enkephalin showed longer-lasting elevated corticosterone levels, indicating a delayed termination of the stress reaction. Importantly, the behavioral and hormonal responses correlated in wild-type but not in knockout mice. Hyperthermia elicited by stress was reduced in animals lacking dynorphin and absent in Penk1(-/-) mice, despite of the heightened behavioral anxiety level of these strains. These results demonstrate an important role on the endogenous opioid system in the integration of behavioral and hormonal stress responses.

Systemic immune challenge activates an intrinsically regulated local inflammatory circuit in the adrenal gland

There is evidence from in vitro studies that inflammatory messengers influence the release of stress hormone via direct effects on the adrenal gland; however, the mechanisms underlying these effects in the intact organism are unknown. Here we demonstrate that systemic inflammation in rats elicited by iv injection of lipopolysaccharide results in dynamic changes in the adrenal immune cell population, implying a rapid depletion of dendritic cells in the inner cortical layer and the recruitment of immature cells to the outer layers. These changes are accompanied by an induced production of IL-1beta and IL-1 receptor type 1 as well as cyclooxygenase-2 and microsomal prostaglandin E synthase-1 in these cells, implying local cytokine-mediated prostaglandin E(2) production in the adrenals, which also displayed prostaglandin E(2) receptors of subtypes 1 and 3 in the cortex and medulla. The IL-1beta expression was also induced by systemically administrated IL-1beta and was in both cases attenuated by IL-1 receptor antagonist, consistent with an autocrine signaling loop. IL-1beta similarly induced expression of cyclooxygenase-2, but the cyclooxygenase-2 expression was, in contrast, further enhanced by IL-1 receptor antagonist. These data demonstrate a mechanism by which systemic inflammatory agents activate an intrinsically regulated local signaling circuit that may influence the adrenals' response to immune stress and may help explain the dissociation between plasma levels of ACTH and corticosteroids during chronic immune perturbations.

Reinstatement of episodic-like memory in rats by neurokinin-1 receptor antagonism

We previously showed that a systemic administration of the selective non-peptide neurokinin-1-receptor (NK-1-R) antagonist SR140333 increases hippocampal acetylcholine levels and facilitates long term memory. In the present study, we investigated whether systemic SR140333 has beneficial effects on episodic-like memory for unique experiences. Rats received either no injection, a vehicle injection or SR140333 at doses of 1, 3 and 9 mg/kg (i.p.) prior to the acquisition of an object memory for what, where and when. In line with previous results, untreated rats showed episodic-like memory, while vehicle-injected rats were impaired. A low dose of 1mg/kg SR140333 reinstated episodic-like memory. This result might be related to the effects of SR140333 on hippocampal cholinergic transmission and/or on the stress-response elicited by the injection procedure. Higher doses of SR140333 (3 and 9 mg/kg) induced psychomotor effects, including stereotypic behaviors and arched posture. Since NK-1-R antagonists have anxiolytic and promestic properties and induce hippocampal acetylcholine release at lower doses, they might be effective in the alleviation of the cognitive deficits and increased anxiety seen in early stages of Alzheimer's disease.

Neuroendocrine Regulation of Frog Adrenocortical Cells by Neurotensin

We previously characterized the primary structure of neurotensin (NT) from an extract of the intestine of the frog Rana esculenta. In this study, we provide evidence for the involvement of NT in the neurocrine regulation of the secretory activity of frog adrenocortical cells. Immunohistochemical studies revealed that the adrenal gland of R. esculenta is innervated by a dense network of NT-immunoreactive fibers. Graded concentrations of frog NT induced a dose-dependent stimulation of corticosterone and aldosterone secretion by frog adrenocortical explants through activation of two receptors with pEC(50) of 9.8 and 6.9. These data support the view that NT, released by nerve fibers within the frog adrenal gland, acts locally to control corticosteroid secretion.

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.

Neuropeptide Y modulates pituitary-adrenal axis activity in the lizard, Podarcis sicula

The role of neuropeptide Y (NPY) in the modulation of the pituitary-adrenal axis activity in a lizard, Podarcis sicula, was investigated by in vivo NPY administration. The effects were evaluated by examination of the morphological and morphometrical features of the tissues as well as the plasma levels of ACTH, corticosterone, aldosterone, norepinephrine, and epinephrine. Intraperitoneally administered NPY (27 nmol /100g body wt) raised ACTH plasma levels (from 5.23+/-0.06 pg/ml in carrier injected specimens to 6.83+/-0.01 pg/ml, 24 h after the injection). In the steroidogenic cells a strong decrease of lipid amount was found; corticosterone plasma level increased from 6.28+/-0.02 ng/ml in carrier injected lizards to 7.96+/-0.01 ng/ml 24 h after the injection); aldosterone levels were raised from 1.88+/-0.02 ng/ml in carrier injected specimens to 6.38+/-0.05 ng/ml 24 h after the experimental treatment. In the chromaffin tissue, an increase in the number of epinephrine cells and a decrease in the number of norepinephrine cells were observed, decreasing the numeric norepinephrine/epinephrine (NE/E) cell ratio, from 1.4/1 of control specimens to 0.5/1 24 h after NPY administration. Moreover, norepinephrine plasma level were elevated from 922+/-4.30 pg/ml in carrier injected specimens to 3075+/-11.30 pg/ml 24 h after NPY administration; epinephrine plasma level increased from 502+/-2.40 pg/ml in carrier injected specimens to 2759+/-8.70 pg/ml 24 h after the experimental treatment. Consistent with these findings, morphological observations showed many chromaffin cells weakly stained and with a reduced content of secretory granules. These results suggest that, in P. sicula, NPY may play a role in the modulation of the pituitary-adrenal axis activity. Previous studies localized NPY in the epinephrine cells of P. sicula adrenal gland; taken together, these results suggest that this peptide might participate in the regulation of adrenal gland activity, enhancing corticosteroid and catecholamine secretion in a paracrine/autocrine manner. The mechanism of action of NPY is discussed.

Nitric oxide plays a role in the regulation of adrenal blood flow and adrenocorticomedullary functions in the llama fetus

The hypothesis that nitric oxide plays a key role in the regulation of adrenal blood flow and plasma concentrations of cortisol and catecholamines under basal and hypoxaemic conditions in the llama fetus was tested. At 0.6-0.8 of gestation, 11 llama fetuses were surgically prepared for long-term recording under anaesthesia with vascular and amniotic catheters. Following recovery all fetuses underwent an experimental protocol based on 1 h of normoxaemia, 1 h of hypoxaemia and 1 h of recovery. In nine fetuses, the protocol occurred during fetal I.V. infusion with saline and in five fetuses during fetal I.V. treatment with the nitric oxide synthase inhibitor L-NAME. Adrenal blood flow was determined by the radiolabelled microsphere method during each of the experimental periods during saline infusion and treatment with L-NAME. Treatment with L-NAME during normoxaemia led to a marked fall in adrenal blood flow and a pronounced increase in plasma catecholamine concentrations, but it did not affect plasma ACTH or cortisol levels. In saline-infused fetuses, acute hypoxaemia elicited an increase in adrenal blood flow and in plasma ACTH, cortisol, adrenaline and noradrenaline concentrations. Treatment with L-NAME did not affect the increase in fetal plasma ACTH, but prevented the increments in adrenal blood flow and in plasma cortisol and adrenaline concentrations during hypoxaemia in the llama fetus. In contrast, L-NAME further enhanced the increase in fetal plasma noradrenaline. These data support the hypothesis that nitric oxide has important roles in the regulation of adrenal blood flow and adrenal corticomedullary functions during normoxaemia and hypoxaemia functions in the late gestation llama fetus.

Neuropeptide Y and the adrenal gland: a review

This paper sets out to review several aspects of NPY and adrenal function, starting with the localisation of NPY in the adrenal, then describing the regulation of NPY release and considering whether the adrenal is a significant source of circulating NPY. The review then describes the regulation of adrenal content of peptide, and finally covers the actions of NPY on the adrenal gland, and the receptor subtypes thought to mediate these effects. The regulation and actions of NPY are discussed with reference to both the adrenal cortex and the medulla.

Deletion of tyrosine hydroxylase gene reveals functional interdependence of adrenocortical and chromaffin cell system in vivo

Catecholamines are produced in the medulla of the adrenal gland and may participate in the intraglandular regulation of its cortex. We analyzed the adrenal structure and function of albino tyrosine hydroxylase-null (TH-null) mice that are deficient in adrenal catecholamine production. Adrenal catecholamines were markedly reduced, and catecholamine histofluorescence was abrogated in 15-day-old TH-null mice. Chromaffin cell structure was strikingly altered at the ultrastructural level with a depletion of chromaffin vesicles and an increase in rough endoplasmic reticulum compared with wild-type mice. Remaining chromaffin vesicles lined up proximally to the cell membrane in preparation for exocytosis providing a "string-of-pearls" appearance. There was a 5-fold increase in the expression of proenkephalin mRNA (502.8 +/- 142% vs. 100 +/- 17.5%, P = 0.016) and a 2-fold increase in the expression of neuropeptide Y (213.4 +/- 41.2% vs. 100 +/- 59.9%, P = 0.014) in the TH-null animals as determined by quantitative TaqMan (Perkin-Elmer) PCR. Accordingly, immunofluorescence for met-enkephalin and neuropeptide tyrosine in these animals was strongly enhanced. The expression of phenylethanolamine N-methyl transferase and chromogranin B mRNA was similar in TH-null and wild-type mice. In TH-null mice, adrenocortical cells were characterized by an increase in liposomes and by tubular mitochondria with reduced internal membranes, suggesting a hypofunctional state of these steroid-producing cells. In accordance with these findings, plasma corticosterone levels were decreased. Plasma ACTH levels were not significantly different in TH-null mice. In conclusion, both the adrenomedullary and adrenocortical systems demonstrate structural and functional changes in catecholamine-deficient TH-null mice, underscoring the great importance of the functional interdependence of these systems in vivo.

Immunohistochemical localization, biochemical characterization, and biological activity of neurotensin in the frog adrenal gland

The primary structure of neurotensin has been recently determined for the frog Rana ridibunda (Endocrinology 139: 4140-4146, 1998). In the present study, we have investigated the distribution and biochemical characterization of neurotensin-like immunoreactivity in the frog adrenal gland, using an antiserum directed against the conserved C-terminal region of the peptide. Neurotensin-like immunoreactivity was detected in two populations of nerve fibers: numerous varicose fibers coursing between adrenal cells, and a few processes located in the walls of blood vessels irrigating the gland. Reversed-phase HPLC analysis of frog adrenal gland extracts revealed the existence of a major peak of neurotensin-like immunoreactivity that exhibited the same retention time as synthetic frog neurotensin. The possible involvement of neurotensin in the regulation of steroid secretion was studied in vitro using perifused frog adrenal slices. For concentrations ranging from 10(-10) to 10(-5) M, synthetic frog neurotensin increased corticosterone and aldosterone production in a dose-dependent manner (EC50 = 1.2 x 10(-9) M and 5.8 x 10(-10) M, respectively). Repeated administration of neurotensin induced a reproducible stimulation of steroid output without any tachyphylaxis. Prolonged administration (3 h) of frog neurotensin caused a transient increase in corticosterone and aldosterone secretion followed by a decline of corticosteroid secretion. Neurotensin also produced a significant stimulation of corticosteroid secretion from dispersed frog adrenal cells. This study demonstrates that neurotensin is located in nerve processes innervating the adrenal gland of amphibians. The results also show that synthetic frog neurotensin exerts a direct stimulatory effect on corticosteroid output. Taken together, these data support the view that neurotensin, released by nerve fibers, may act as a local regulator of corticosteroid secretion.

How enteral feeding options influence corticosterone patterns in rats

Even with all the nutritional research conducted to date, it is not clear which enteral nutrition delivery and composition options are most physiologically sound. Glucocorticoid temporal patterns are reported to be shifted or disrupted with restricted feeding schedules, but because of intermittent sampling, temporal patterns have not been completely depicted. The purpose of this study was to characterize corticosterone temporal patterns while systematically varying selected enteral feeding options in a well-established nutritional animal model. A 2 x 2 x 2 x 2 randomized block experimental design was used in which enteral feeding schedules, delivery methods, kilocalorie levels (kcal), and fiber contents were systematically varied in rats (n = 80), and plasma corticosterone was measured by 125I radioimmunoassay. Blood samples were drawn hourly over 24 h. With cosinor analysis, 24-h and 12-h corticosterone rhythmic components were tested in each feeding group. Five of 16 feeding groups had a significant (p < or = 0.05) 24-h rhythmic component, and 3 more showed a trend (p > 0.05 < 0.10); 7 of these groups were on 24-h feeding schedules. When rhythmic components were detectable, groups receiving high-fiber formula displayed more uniform rhythm characteristics than did no-fiber groups. Only 1 group had a significant 12-h rhythmic component, and 1 showed a trend. Both were on 12-h, high-fiber restricted kcal feedings. In this small animal sample, no one enteral feeding option guaranteed a 24-h corticosterone pattern. The option coming closest was formula delivered on a 24-h schedule. This temporal pattern is one aspect to consider in enteral nutrition. The underlying mechanisms have yet to be elucidated.

Role of tachykinins in the regulation of the hypothalamo-pituitary-adrenal axis

Tachykinins are a family of neuropeptides, which act by binding to three main subtypes of G protein-coupled receptors, named NK1, NK2 and NK3. Tachykinins are contained in both nerve fibers and secretory cells of the hypothalamo-pituitary-adrenal (HPA) axis, and evidence indicates that they take part in the functional control of it. Tachykinins involved in this function include substance P (SP), neuropeptide K and its derivative neurokinin A (NKA), and neurokinin B, which preferentially bind to NK1, NK2 and NK3 receptors, respectively. NK1 agonists exert an inhibitory effect on the hypothalamo pituitary CRH/ACTH system, while NK2 and perhaps NK3 agonists stimulate it, thereby controlling the secretion and growth of the adrenal cortex via circulating ACTH. Intra-adrenal tachykinins may also affect the cortex function. Their direct action on adrenocortical cells is doubtful and probably pharmacologic in nature, but several investigations suggest that tachykinins indirectly stimulate the cortex by acting on medullary chromaffin cells, which in turn exert a paracrine control on adrenocortical cells. SP enhances aldosterone production of zona glomerulosa by eliciting catecholamine secretion; neuropeptide K and NKA raise glucocorticoid production of zonae fasciculata and reticularis through the activation of the intramedullary CRH/ACTH system. The relevance of these effects of tachykinins under basal conditions is questionable, although there are indications that SP is involved in the maintenance of a normal growth and steroidogenic capacity of rat zona glomerulosa, and that SP and NKA play an important role in the stimulation of the adrenal growth during the fetal life. In contrast, evidence has been provided that the role of tachykinins, and especially of SP, could become very relevant under paraphysiological (e.g., physical or inflammatory stresses) or pathological conditions (e.g., ACTH-secreting pituitary tumors), when an excess of steroid-hormone production has to be counteracted.

Role of VIP, PACAP, and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a family of regulatory peptides that are widely distributed in the body and share numerous biologic actions. The two peptides display a remarkable amino acid-sequence homology, and bind to a class of G protein-coupled receptors, named PACAP/VIP receptors (PVRs), whose signaling mechanism mainly involves the activation of adenylate-cyclase and phospholipase-C cascades. A large body of evidence suggests that VIP and PACAP play a role in the control of the hypothalamo--pituitary-adrenal (HPA) axis, almost exclusively acting in a paracrine manner, since their blood concentration is very low. VIP and PACAP are contained in both nerve fibers and neurons of the hypothalamus, and VIP, but not PACAP, is also synthesized in the pituitary gland. Both peptides are expressed in the adrenal gland, and especially in medullary chromaffin cells. All the components of the HPA axis are provided with PVRs. VIP and PACAP enhance pituitary ACTH secretion, VIP by eliciting the hypothalamic release of CRH and potentiating its secretagogue action, and PACAP by directly stimulating pituitary corticotropes. Through this central mechanism, VIP and PACAP may increase mineralo- and glucocorticoid secretion of the adrenal cortex. VIP but not PACAP also exerts a weak direct secretagogue action on adrenocortical cells by activating both PVRs and probably a subtype of ACTH receptors. VIP and PACAP raise aldosterone production via a paracrine indirect mechanism involving the stimulation of medullary chromaffin cells to release catecholamines, which in turn enhance the secretion of zona glomerulosa cells via a beta-adrenoceptor-mediated mechanism. PACAP appears to be able to evoke a glucocorticoid response through the activation, at least in the rat, of the intramedullary CRH/ACTH system. The relevance of these effects of VIP and PACAP under basal conditions is questionable, although there are indications that endogenous VIP is involved in the maintenance of the normal growth and steroidogenic capacity of rat adrenal cortex. However, indirect evidence suggests that these peptides might play a relevant role under paraphysiological conditions (e.g., in the mediation of HPA axis responses to cold and inflammatory stresses) or may be somehow involved in the pathogenesis of Cushing disease or some case of hyperaldosteronism associated with secreting pheochromocytomas.

Stimulatory effect of the substance P antagonist spantide-II on aldosterone secretion of dispersed rat zona glomerulosa cells

Substance P (SP) did not affect either basal or agonist-stimulated aldosterone production by dispersed rat zona glomerulosa (ZG) cells. In contrast, the SP-receptor antagonist spantide-II (SPA), at 10(-8)/10(-6) M concentrations, markedly raised basal and 10(-9) M ACTH, but not 10(-9) M angiotensin II-stimulated aldosterone secretion. The secretagogue effect of 10(-6) M SPA was annulled by SP (10(-6) M) and the protein kinase (PK)-C inhibitor Ro31-8220 (10(-6) M), but was unaffected by the PKA inhibitor H-89 (10(-5) M). In light of these findings the following conclusions can be drawn: (i) SP does not exert a physiologically relevant direct modulatory action on aldosterone secretion of rat ZG cells; (ii) a receptor-independent inhibitory interaction is likely to occur between SP and SPA molecules; and (iii) SPA activates, through a receptor-independent mechanism, phosphoinositide signaling pathway in rat ZG cells.

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

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.