Effects of the infusion with ACTH or CRH on the secretory activity of rat adrenal cortex

Pharmacodynamic and pharmacokinetic characterization of the aldosterone synthase inhibitor FAD286 in two rodent models of hyperaldosteronism: comparison with the 11beta-hydroxylase inhibitor metyrapone

Aldosterone synthase (CYP11B2) inhibitors (ASIs) represent an attractive therapeutic approach for mitigating the untoward effects of aldosterone. We characterized the pharmacokinetic/pharmacodynamic relationships of a prototypical ASI, (+)-(5R)-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-5-yl]benzonitrile hydrochloride (CGS020286A, FAD286, FAD) and compared these profiles to those of the 11beta-hydroxylase inhibitor metyrapone (MET) in two rodent models of secondary hyperaldosteronism and corticosteronism. In chronically cannulated Sprague-Dawley rats, angiotensin II (ANG II) (300 ng/kg bolus + 100 ng/kg/min infusion) or adrenocorticotropin (100 ng/kg + 30 ng/kg/min) acutely elevated plasma aldosterone concentration (PAC) from approximately 0.26 nM to a sustained level of approximately 2.5 nM for 9 h. Adrenocorticotropin but not ANG II elicited a sustained increase in plasma corticosterone concentration (PCC) from approximately 300 to approximately 1340 nM. After 1 h of Ang II or adrenocorticotropin infusion, FAD (0.01-100 mg/kg p.o.) or MET (0.1-300 mg/kg p.o.) dose- and drug plasma concentration-dependently reduced the elevated PACs over the ensuing 8 h. FAD was approximately 12 times more dose-potent than MET in reducing PAC but of similar or slightly greater potency on a plasma drug concentration basis. Both agents also decreased PCC in the adrenocorticotropin model at relatively higher doses and with similar dose potencies, whereas FAD was 6-fold weaker based on drug exposures. FAD was approximately 50-fold selective for reducing PAC versus PCC, whereas MET was only approximately 3-fold selective. We conclude that FAD is a potent, orally active, and relatively selective ASI in two rat models of hyperaldosteronism. MET is an order of magnitude less selective than FAD but is, nevertheless, more potent as an ASI than as an 11beta-hydroxylase inhibitor.

Influence of Stress and Nutrition on Cattle Immunity

Today, the scientific community readily embraces the fact that stress and nutrition impact every physiologic process in the body. At last, the specific mechanisms by which stress and nutrition affect the immune function are being elucidated. The debate among animal scientists concerning the definition and quantification of stress as it relates to animal productivity and well-being is ongoing. However, an increased appreciation and understanding of the effects of stress on livestock production has emerged throughout the scientific community and with livestock producers. The intent of this article is to provide an overview of the general concepts of stress and immunology, and to review the effects of stress and nutrition on the immune system of cattle.

Corticotropin-releasing hormone receptor expression on normal and tumorous human adrenocortical cells

Corticotropin-releasing hormone (CRH) is not only the principal regulator of the central hypothalamic-pituitary-adrenal (HPA) axis but also exerts direct actions on peripheral tissues. We analyzed the expression of CRH receptors in microdissected preparations of normal human adrenal glands and in adrenocortical and adrenomedullary tumors, employing immunohistochemistry, quantitative RT-PCR of microdissected adrenal tissues, and in situ hybridization. The effect of CRH on adrenal steroidogenesis was tested in adrenal cells. Immunoreactive CRH1R was found primarily within the zona reticularis. In addition, we found a higher expression of CRH type-1 and 2 receptors mRNAs in preparations of adrenal cortices as compared to pheochromocytomas, a 6-fold increase in preparations of clinically unapparent adrenocortical adenomas, and a 10- to 60-fold increase in cortisol-producing adrenal adenomas. Stimulation of the adrenal tumor cell line NCI-H295R with CRH elicited a 1.4-fold increase in DHEA secretion. This result could be reproduced in a culture of primary human adrenocortical cells. We conclude that adrenocortical cells exhibit a higher expression of functional CRH receptors than chromaffin cells and that CRH acts on adrenal DHEA production. The data support the assertion of a direct action of CRH on human adrenocortical cells in addition to an intra-adrenal CRH receptor/adrenocorticotropin system. Enhanced CRH1R expression may be involved in adrenocortical tumorigenesis.

Mifepristone modulation of ACTH and CRH regulation of bovine adrenocorticosteroidogenesis in vitro

Mifepristone (RU486), bovine corticotropin-releasing hormone (CRH), arginine vasopressin (VP), adrenocorticotropin (ACTH1-24), and protein kinase activators (forskolin, [FSK]; phorbol 12-myristate 13-acetate [PMA]) were used in vitro to investigate their direct effect on adrenocorticosteroidogenesis. Bovine adrenocortical fasciculata/reticularis cells (2 x 10(5) viable cells/well) were cultured for 3 d in medium supplemented with 10% fetal calf serum. After incubation for an additional 24 hr in serum-free medium, cells were treated with serum-free medium alone (Control) or various concentrations of ACTH, CRH, VP, FSK, PMA, RU486, and/or various concentrations for 1, 2, 4, or 24 hr. Medium content of cortisol and progesterone were determined by radioimmunoassays. ACTH, CRH, FSK, and PMA each stimulated (P < 0.05) secretion of cortisol in time- and dose-related manners. Although these agents stimulated (P < 0.05) secretion of progesterone in a dose-related manner, medium content of progesterone declined (P < 0.05) over time. The minimal effective doses of ACTH and CRH required to stimulate (P < 0.05) secretion of cortisol relative to the Control over a 4-hr culture period were 0.01 nM and 3 nM, respectively. Relative to observations at 1 hr posttreatment, 24-hr treatment with ACTH or CRH increased the medium content of cortisol by an additional 19.8- and 48-fold, respectively (whereas content of progesterone declined over that time period). VP-stimulated secretion of cortisol was time- (P < 0.05) but not dose-related. Specifically, by 24-hr posttreatment, the medium content of cortisol was increased (P < 0.05) 4.6-fold relative to the quantity of cortisol secreted by 1-hr postaddition of VP (0.01 to 1 microM). Co-treatment with RU486 (1 microM) decreased (p < 0.05) FSK-, ACTH- and CRH-stimulated secretion of cortisol by 77, 27, and 56%, respectively. Similarly, the stimulatory effects of ACTH and CRH on progesterone secretion were reduced (P < 0.05) by 40 and 22%, respectively, by co-addition of RU486. The inhibitory action of RU486 on production of cortisol was no longer apparent by 24 hr after treatment. These observations indicate that RU486 can act as a steroid agonist and as well as an antagonist. These data characterize time- and dose-related direct actions of ACTH, CRH, and RU486 on adrenocorticosteroidogenesis. This information will assist efforts to clarify complex intra-adrenal interactions of neurohormones, growth factors, and endogenous steroids.

Low-dose ovine corticotropin-releasing hormone stimulation test in diabetes mellitus with or without neuropathy

The function of the hypothalamic-pituitary-adrenal (HPA) axis was evaluated in insulin-dependent diabetics without (group I, n = 10) or with (group II, n = 10) established symptomatic neuropathy and in age- and weight-matched normal controls (n = 11). Since the corticotropin (ACTH)/cortisol response to the minimal-effective dose of corticotropin-releasing hormone ([CRH] 0.03 microgram/kg body weight) represents a useful tool for HPA axis examination, all subjects were tested with the low-dose ovine CRH stimulation test. Experiments started at 8:30 AM, when CRH was injected after two basal blood samples were withdrawn, and lasted 2 hours. Basal serum levels of ACTH were similar in the three groups. Administration of CRH induced a small but significant increase in ACTH levels in all subjects; however, the CRH-induced ACTH increase was significantly higher in normal controls than in diabetic groups I and II. Furthermore, a significantly lower ACTH response was observed in group II than in group I. In contrast, basal and CRH-induced cortisol levels were significantly higher in diabetics than in normal controls. Comparisons between diabetic groups showed that both basal and stimulated cortisol secretion was significantly higher in group II than in group I. When peak ACTH responses to CRH and basal cortisol levels were combined, a significant negative correlation was found (r = .545, P < .02). These data show that even uncomplicated diabetes mellitus is associated with adrenal hyperfunction. Such an alteration is more pronounced in the presence of neuropathy.

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.

Evidence that an extrahypothalamic pituitary corticotropin-releasing hormone (CRH)/adrenocorticotropin (ACTH) system controls adrenal growth and secretion in rats

Within two weeks, hypophysectomy induced in rats a striking decrease in the level of circulating ACTH (the concentration of which was at the limit of sensitivity of our assay system), coupled with a net reduction in the plasma corticosterone concentration and an evident adrenal atrophy. Zona fasciculata, the main producer of glucocorticoids, was decreased in volume, due to a lowering in both the number and average volume of its parenchymal cells. Subcutaneous ACTH infusion (0.1 pmol.min-1), administered during the last week following hypophysectomy, restored the normal blood level of ACTH and completely reversed all effects of hypophysectomy on the adrenals. Subcutaneous infusion for one week with alpha-helical-CRH or corticotropin-inhibiting peptide (1 nmol.min-1), which are competitive inhibitors of CRH and ACTH, evoked a further significant lowering of plasma corticosterone concentration and markedly enhanced adrenal atrophy in hypophysectomized rats. These findings strongly suggest that an extrahypothalamic pituitary CRH/ACTH system may be involved in the maintenance of the growth and steroidogenic secretory activity of the rat adrenal cortex.

Hypothalamic-pituitary-adrenal function in non-AIDS patients with advanced HIV infection

Patients with acquired immune deficiency syndrome (AIDS) are reported to have increased basal cortisol and reduced stimulated cortisol release, but the dysfunction in the hypothalamic-pituitary-adrenal (HPA) axis is not yet understood in patients with human immunodeficiency virus (HIV) infection during the advanced stage of disease that precedes the development of AIDS. To understand the status of the HPA axis during this phase of HIV infection, 25 non-AIDS ambulatory patients with advanced HIV infection and without evidence of adrenal or pituitary insufficiency were studied. Ovine corticotropin-releasing hormone was administered (1 microgram/kg BW) intravenously and plasma cortisol and adrenocorticotropin (ACTH) were measured over the following 120 minutes. Based on a standard response curve, obtained from CRH testing of 10 HIV negative volunteers with no HPA abnormalities, 13 patients were found to have normal response (group 1), 6 patients had reduced ACTH and cortisol response (group 2) and 6 patients had normal ACTH with reduced cortisol response (group 3). Basal cortisol and basal ACTH were comparable for control subjects and groups 1, 2, and 3. This suggests that, in advanced non-AIDS HIV patients with no clinical evidence of pituitary or adrenal disease, about 25% (group 2) have reduced pituitary reserve with high basal ACTH and cortisol, and about 25% (group 3) have reduced adrenal reserve with high basal cortisol and inappropriately normal basal ACTH, whereas about 50% (group 1) maintain normal HPA axis activity with increased basal cortisol secretion. The exact physiopathologic mechanism is not yet known, but an enhanced CRH production by the hypothalamus may explain the alterations in the HPA axis in advanced HIV disease.

Structure and dynamics of adrenal mitochondria following stimulation with corticotropin releasing hormone

The mitochondria of rat adrenals were investigated qualitatively and quantitatively in different functional states of the adrenal cortex. Following stimulation of the animals with corticotropin releasing hormone (CRH), the corticosterone serum levels reached a maximum 1 hour after stimulation with CRH. The amount of inner mitochondrial membrane within the zona fasciculata increased showing a biphasic time course, with a first maximum 2 hours and a second maximum 8 hours after stimulation. In contrast, a significant rise of mitochondrial volume occurred only 24 hours after CRH stimulation. Therefore, the dense vesicularization of mitochondrial cristae may constitute an early process to enhance the steroidogenic capacity of these cells. Within cells of the transition zone between zona glomerulosa and zona fasciculata, we could depict a special type of mitochondria with characteristic crescent-like cristae only seen after stimulation with CRH. This type of mitochondria may represent an intermediate form between mitochondria of zona glomerulosa and zona fasciculata underlining the impressive transformational capacity of adrenocortical mitochondria. After hypophysectomy, zona fasciculata cells contained mitochondria with tubular inner membranes, representing a hypofunctional state. In contrast, the hypofunctional state after hypophysectomy and the hyperfunctional state after stimulation of the adrenal cortex via CRH injection did not appear to correlate with the morphology of mitochondria from the zona reticularis and adrenal medulla.

Corticotropin-independent effect of ovine corticotropin-releasing hormone on cortisol release in man

The effect of corticotropin-releasing hormone (CRH), independent of adrenocorticotropin hormone (ACTH), was evaluated in nine healthy individuals. Cortisol release and corresponding ACTH production were determined after separate intravenous administration of ovine-CRH (1 micrograms/kg BW) and insulin inducing hypoglycemia (0.1 u/kg BW). Adrenocorticotropin hormone (1-24; 250 micrograms intravenous bolus) revealed an adequate adrenal reserve capacity in all subjects. At the time of peak cortisol response following CRH and insulin administration, IR-cortisol increments were 14 +/- 1 micrograms/dl and 9 +/- 1 micrograms/dl (mean +/- SE), respectively (p less than .05); whereas ACTH (IR-ACTH) increments were 40 +/- 10 ng/l and 53 +/- 14 ng/l, respectively. The cortisol increment/ACTH increment ratios were 0.53 +/- 0.09 and 0/36 +/- 0.09, respectively (p less than 0.05), suggesting an ACTH-independent effect of CRH on cortisol production. The authors speculate that CRH may have a direct effect on the human adrenal gland or it may release ACTH-like factors that stimulate the human adrenal cortex.

Neurotensin enhances plasma adrenocorticotropin concentration by stimulating corticotropin-releasing hormone secretion

The systemic administration of neurotensin (NT) dose-dependently increased plasma adrenocorticotropin (ACTH) concentration in rats, and this effect was annulled by (alpha-helical)-CRH9-41, an antagonist of corticotropin-releasing hormone (CRH). The systemic administration of [D-Trp11]-neurotensin (NT-A), a specific NT antagonist, dose-dependently reduced the basal level of circulating ACTH, and this effect was blunted by NT injection. The ACTH inhibitory action of NT-A was completely overcome by the administration of CRH. Taken together, our findings suggest that NT plays a physiologic role in rats, as ACTH secretagogue, and that the mechanism underlying this action of NT involves the stimulation of CRH release.

Comparison of ACTH and corticotropin-releasing hormone effects on rat adrenal steroidogenesis in vitro

The effects of equimolar concentrations (10(-9) M) of ACTH and corticotropin-releasing hormone (CRH) on the secretory activity of zona glomerulosa (ZG) and zonae fasciculata and reticularis (ZF/ZR) of rat adrenals were investigated in vitro by high-pressure liquid chromatography. ACTH enhanced the output of all the post-progesterone steroids (11-deoxycorticosterone, 18-hydroxy-11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone, and aldosterone) both by isolated ZG or ZF/ZR cells and by adrenal slices. CRH raised the secretory activity exclusively of adrenal slices, and its effect was less than half that of ACTH. However, the extents to which the various post-progesterone hormones contributed to the ACTH- or CRH-induced rises in the overall adrenal secretory activity were similar. The hypothesis is discussed that CRH acts on the rat adrenal gland by eliciting a local production of ACTH.