Corticotropin-releasing hormone-like axons in the adrenal glands of fetal and postnatal sheep

A specific CRH antagonist attenuates ACTH-stimulated cortisol secretion in ovine adrenocortical cells

Corticotropin releasing hormone (CRH) has been detected in the adrenal gland of many species and may be involved in regulation of glucocorticoid secretion. In cultured human fetal adrenal definitive/transitional zone cells, CRH upregulates the adrenocorticotropic hormone (ACTH) receptor and steroidogenic enzymes and is blocked by the selective CRH type 1 receptor (CRH(1)) antagonist, antalarmin. Based on these findings and evidence that antalarmin infusion into sheep suppressed prepartum increases in cortisol, we hypothesized that antalarmin would influence adrenal cortisol secretion. Antalarmin strongly attenuated ACTH and forskolin (FSK)-stimulated cortisol and cyclic adenosine monophosphate (cAMP) release from cultured ovine adrenocortical cells but did not prevent ACTH binding to cells or ACTH-induced proliferation in adult cells. Corticotropin releasing hormone was minimally effective as a secretagogue but increased the cortisol response to subsequent ACTH. These results suggest that antalarmin attenuates ACTH-induced cortisol secretion from cultured ovine adrenal cortical cells at a site distal to the ACTH receptor. Although CRH may modulate the secretory response to ACTH, it is probably not a direct cortisol secretagogue in the sheep.

Overexpression of corticotropin-releasing hormone in transgenic mice and chronic stress-like autonomic and physiological alterations

To gain a greater insight into the relationship between hyperactivity of the corticotropin-releasing hormone (CRH) system and autonomic and physiological changes associated with chronic stress, we developed a transgenic mouse model of central CRH overproduction. The extent of central and peripheral CRH overexpression, and the amount of bioactive CRH in the hypothalamus were determined in two lines of CRH-overexpressing (CRH-OE) mice. Furthermore, 24 h patterns of body temperature, heart rate, and activity were assessed using radiotelemetry, as well as cumulative water and food consumption and body weight gain over a 7-day period. CRH-OE mice showed increased amounts of CRH peptide and mRNA only in the central nervous system. Despite the presence of the same CRH transgene in their genome, only in one of the two established lines of CRH-OE mice (line 2122, but not 2123) was overexpression of CRH associated with increased levels of bioactive CRH in the hypothalamus, increased body temperature and heart rate (predominantly during the light (inactive) phase of the diurnal cycle), decreased heart rate variability during the dark (active) phase, and increased food and water consumption, when compared with littermate wildtype mice. Because line 2122 of the CRH transgenic mice showed chronic stress-like neuroendocrine and autonomic changes, these mice appear to represent a valid animal model for chronic stress and might be valuable in the research on the consequences of CRH excess in situations of chronic stress.

HPA axis dysregulation in mice overexpressing corticotropin releasing hormone

BACKGROUND

Hypersecretion of corticotropin-releasing hormone (CRH) in the brain has been implicated in stress-related human pathologies. We developed a transgenic mouse line overexpressing CRH (CRH-OE) exclusively in neural tissues to assess the effect of long-term CRH overproduction on regulation of the hypothalamic-pituitary-adrenal (HPA) axis.

METHODS

Male transgenic CRH-OE(2122) mice on a C57BL/6J background were used. Littermate wildtype mice served as control animals. Basal plasma corticotropin and corticosterone concentrations were measured, and adrenal gland weight was determined. A dexamethasone suppression test measured the effects of long-term CRH hypersecretion on negative feedback control. Additionally, we measured plasma corticosterone concentrations in reaction to stress.

RESULTS

CRH-OE(2122) mice showed elevated basal plasma corticosterone concentrations, hypertrophy of the adrenal gland, and dexamethasone nonsuppression. Basal plasma ACTH concentrations of wildtype and CRH-OE(2122) mice did not differ significantly. In reaction to stress, CRH-OE(2122) mice showed a normal corticosterone response.

CONCLUSIONS

The HPA axis abnormalities observed in CRH-OE(2122) mice suggest that long-term hypersecretion of CRH in the brain can be a main cause of HPA axis dysregulation. The alterations in HPA axis regulation are reminiscent of changes reported in major depressive disorder. As such, these CRH -OE(2122) mice may model the neuroendocrine changes observed in major depressive disorder.

Corticotropin-releasing hormone stimulates steroidogenesis in cultured human adrenal cells

The effects of corticotropin releasing hormone (CRH) on steroid production by cultures of human fetal adrenal cells was investigated. We found that CRH, at concentrations that have been reported to exist in human fetal serum, stimulated dehydroepiandrosterone sulfate (DS) and cortisol production by cultured fetal zone and neocortical zone cells. A dose-dependent increase in secretion of both steroids was noted, with the cortisol pathway being preferentially enhanced by CRH at high concentrations. Pretreatment of adrenal cells for 3 days made them more responsive to ACTH stimulation and such effects were dose-dependent also. Inclusion of the antagonist, alpha-helical CRH (9-41) blocked CRH-induced stimulation of DS and cortisol over a broad dose range and also interfered with the augmentation of cortisol secretion noted after ACTH in CRH treated cells. CRH had no effects on adrenal cell proliferation or total cell protein. These studies are suggestive that CRH, either of systemic origin or else produced within the adrenal itself, has the potential to be a modulator of adrenal steroid production in the human.

Ontogeny of innervation of rat and ovine fetal adrenals

The formation of adrenocortical zonation occurs in rats during late gestation. Since adult cortical function is modulated by neural mediators, it is possible that the development of differentiated function is dependent on cortical innervation. The goal of this study was to compare the pattern and timing of rodent and ovine adrenal innervation during late organogenesis by staining with antibodies directed against the neuropeptides vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and neuropeptide tyrosine (NPY) and the catecholamine biosynthetic enzyme, tyrosine hydroxylase (TOH). Rat adrenals were collected from fetal days 17-21 (term=21 days) and ovine adrenals from fetal days 101-136 (term=145 days). Adrenals were fixed, cryosectioned at 100 microns and immunostained using Cy3-conjugated secondary antibodies. In both species, staining of VIP, CGRP, NPY and TOH fibers was observed in the capsule and subcapsular layers of the cortex during gestation. In late gestation, VIP- and NPY-positive ganglions cells were observed near the medulla extending processes toward the outer cortex; in ovine adrenals, fibers from ganglion cells appeared to surround nests of outer cortical (presumably, zona glomerulosa) cells. These data show that phenotypically distinct neural elements appear at different stages of adrenocortical development. The presence of neural elements in contact with adrenal cortical cells supports the possibility for neural control of adrenocortical development.

Chemoreflex contribution to adrenocortical function during acute hypoxemia in the llama fetus at 0.6 to 0.7 of gestation

This study tested the hypothesis that the fetal llama, a species adapted to the chronic hypoxia of life at high altitude, demonstrates a potent carotid chemoreflex influence on adrenocortical responses during acute hypoxemia. Plasma ACTH and cortisol concentrations, and mesencephalic and adrenal blood flows were measured during a 1-h period of acute hypoxemia in six intact and four carotid sinus-denervated llama fetuses at 0.6-0.7 of gestation. Fetal PaO2 was reduced from approximately 23 to about 14 mm Hg in both intact and carotid-denervated groups during acute hypoxemia. During hypoxemia, fetal plasma ACTH, adrenal blood flow, and, therefore, delivery of ACTH to the adrenals increased to similar extents in both intact and carotid-denervated fetal llamas. Despite this, the increase in plasma cortisol in hypoxemia in intact fetuses was absent in carotid-denervated fetuses. In addition, the increase in delivery of cortisol to the mesencephalon calculated in intact fetuses during hypoxemia did not occur in the carotid-denervated group. These data suggest that the integrity of the carotid chemoreceptors is indispensable to cortisol release during acute hypoxemia in the llama fetus, even at 0.6-0.7 of gestation.

Source of corticotropin-releasing hormone-like innervation of the adrenal glands of fetal and postnatal sheep

In pre- and postnatal sheep the irregularly shaped adrenal corticomedullary interface is innervated by corticotropin-releasing hormone (CRH)-like beaded fibers. Since CRH-like staining is also seen in the splanchnic nerves, we examined the intermediolateral sympathetic columns (ISC) of the thoracic (T) spinal cords (segments 5-13) of 12 pre- and postnatal sheep for CRH-like immunocytochemical reactivity and in a subset of fetuses, fluorogold immunoreactivity after fluorogold injection to the left adrenal medulla. All animals had CRH-like immunopositive neurons in the ISC from all thoracic segments. The number of CRH-like positive neurons per thoracic segment did not change either from anterior to posterior within groups nor were there differences between groups. Fluorogold immunopositive neurons occurred in the ISC of all injected animals from T5 to T13. Upon double immunostaining, some ISC CRH-like immunopositive neurons also demonstrated fluorogold immunopositivity. Taken together, these studies indicate that there are CRH-like immunopositive neurons in the ISC of pre- and postnatal sheep and that some of these CRH-like immunopositive neurons innervate the adrenal medulla.