Control Of Adrenal Function Research Articles

Acute hypoxia in neonatal rats: a novel ACTH‐and cAMP‐independent control of adrenal function

The hypothalamic‐pituitary‐adrenal (HPA) axis plays a critical role in the adaptation to neonatal hypoxia. The classic adrenocortical response involves ACTH‐stimulated corticosterone (Cort) synthesis mediated by increased cAMP. We previously demonstrated that, in the neonatal rat, the Cort response to acute hypoxia shifts from ACTH‐independence to ACTH‐dependence between postnatal day (PD) 2 and 8. We now correlate plasma ACTH and Cort responses with adrenal cAMP content from PD2 and PD8 rats exposed to acute hypoxia. In PD2 rats, hypoxia elicited a minimal increase in plasma ACTH, no change in adrenal cAMP content, but a robust increase in plasma Cort. In PD8 rats, hypoxia elicited large increases in plasma ACTH, adrenal cAMP content, and plasma Cort, consistent with the classic mechanism of adrenocortical control. Preliminary results using adrenocortical cells in vitro to bioassay plasma corticotropic activity showed a hypoxia‐induced 3.5‐fold increase in PD2 plasma and a 1.7 fold increase in PD8 plasma, suggesting a humoral mechanism of stimulation of Cort in PD2 rats. The data indicate that the robust plasma Cort response to hypoxia in the PD2 rat does not require ACTH‐mediated increases in cAMP production in the adrenal. This ACTH‐and cAMP‐independent control of adrenocortical function, exhibited only in the newborn rat, may be due to a novel hormonal mechanism of zona fasciculata control. NSF IOS1025199

Genetic modifications of mouse proopiomelanocortin peptide processing

Pro-opiomelanocortin (POMC) is a prohormone which undergoes extensive tissue and cell specific post-translational processing producing a number of active peptides with diverse biological roles ranging from control of adrenal function to pigmentation to the regulation of feeding. One approach to unraveling the complexities of the POMC system is to engineer mouse mutants which lack specific POMC peptides. We describe here the design, generation, validation, and preliminary analysis of one such partial POMC mutant specifically lacking α-MSH. In contrast to POMC null mutant mice, mice lacking α-MSH in the presence of all other POMC peptides maintain adrenal structures and produce corticosterone comparable to wildtype littermates; however, they still have decreased levels of aldosterone, as found in POMC null mutant mice. Our findings demonstrate that α-MSH is not needed for maintenance of adrenal structure or for corticosterone production, but is needed for aldosterone production. These data demonstrate that mouse strains generated with precise genetic modifications of POMC peptide processing can answer questions about POMC peptide function. Further analysis of this and additional strains of mice with modified POMC peptide processing patterns will open up a novel avenue for studying the roles of individual POMC peptides.

Presence of corticotropin-releasing-hormone receptor on adrenocortical cells

Corticotropin-releasing hormone (CRH) is not only the principal regulator of the stress system but also exerts profound actions on peripheral tissues. Its control over adrenal steroidogenesis is accomplished through activation of the hypothalamo-pituitary-adrenal (HPA) axis and the sympathoadrenal (SA) system. However, there is growing evidence for a direct involvement in control of adrenal function on the level of the adrenal gland. Most effects of CRH on adrenal steroidogenesis have been attributed to a paracrine action of medulla-derived corticotropin (ACTH)-like factors in a lokal CRH receptor / ACTH system. But growing evidence for a direct action of CRH on the adrenal cortex also exists. Therefore, we studied the distribution of immunoreactive CRH-receptor protein employing immunohistochemistry of paraffin-embedded sections of three normal human adrenal glands, four adrenocortical and two adrenomedullary tumors. In addition, we examined expression of CRH type 1 receptor mRNA in microdissected preparations of the adrenal cortex from two normal human adrenal glands, in two medulla-free adrenal incidentalomas, one cortisol-producing adrenal adenoma and in two cortex-free pheochromocytomas. While adrenocortical cells could be immunolabelled with the antibody directed to CRH type 1/2 receptors in normal human adrenal glands in all three zones and in adrenocortical tumors, adrenal chromaffin cells could not, neither in sections of normal human adrenals nor in pheochromocytomas. In addition, the data document a higher expression of the type 1 CRH receptor mRNA in the preparations which were rich in adrenocortical cells and in preparations of adrenocortical tumors in comparence to the tissue obtained from pheochromocytomas. We conclude that adrenocortical cells exhibit a higher expression of CRH receptors than adrenal chromaffin cells as shown on the mRNA and protein level. The data support the hypothesis of a direct action of CRH on adrenocortical cells in addition to its action via an intraadrenal CRH receptor / ACTH system.

Vasopressin: A potent autocrine/paracrine regulator of mammal adrenal functions.

The control of adrenal functions by locally secreted neuropeptides or neutotransmitters is of great physiological importance. Vasopressin (VP) is one of these autocrine/paracrine regulators. We demonstrated by RT-PCR and perifusion experiments that rat and human adrenal medulla expressed and released vasopressin under basal conditions and under stimulation by acetylcholine. Intra-adrenal concentrations of VP may be sufficient to activate adrenal VP receptors. In the cortex, only the V1a receptor subtype has been detected. It triggered both steroid secretion and cortical growth. In the medulla, both V1a and V1b receptor subtypes were expressed. V1b receptors were mainly present on chromaffin cells and stimulated catecholamine secretion. The role of the V1a receptor remains unclear. Pathophysiological studies also revealed that human pheochromocytoma did not overexpress vasopressin receptors but might oversecrete vasopressin causing high plasma VP concentrations and elevated blood pressure.

Human adrenal cells express tumor necrosis factor-alpha messenger ribonucleic acid: evidence for paracrine control of adrenal function.

Tumor necrosis factor (TNF) is gaining increasing importance in clinical medicine. It plays a role in the interaction of the immune system with the hypothalamic-pituitary-adrenal axis. In the present study various morphological methods, including immunohistochemistry, electron microscopy, and in situ hybridization were applied to characterize the localization and distribution of TNF in the human adrenal gland. Double immunostaining revealed an astonishing degree of intermingling of steroid-producing cells and chromaffin cells. Macrophages could be found in all regions of the adrenal gland, but particularly in the transition zone of cortex and medulla. The steroid-producing cells of the inner zone of the cortex express major histocompatibility complex class II molecules. On the ultrastructural level, immune cells, steroid cells, and catecholamine-producing cells were found in direct contact. The combination of immunohistochemistry and in situ hybridization was optimally suited to define the exact cellular source of TNF in the human adrenal. TNF is produced in macrophages, but above all in 17 alpha-hydroxylase-positive cells (steroid-producing cells) in the zona reticularis and medulla. No signal was found in chromaffin cells. TNF may induce major histocompatibility complex class II in human adrenal gland in a paracrine or autocrine manner. It is concluded that TNF may have an important role in normal human adrenal physiology.

Chemical codes of sensory neurons innervating the guinea-pig adrenal gland

Retrograde neuronal tracing in combination with double-labelling immunofluorescence was applied to distinguish the chemical coding of guinea-pig primary sensory neurons projecting to the adrenal medulla and cortex. Seven subpopulations of retrogradely traced neurons were identified in thoracic spinal ganglia T1-L1. Five subpopulations contained immunolabelling either for calcitonin gene-related peptide (CGRP) alone (I), or for CGRP, together with substance P (II), substance P/dynorphin (III), substance P/cholecystokinin (IV), and substance P/nitric oxide synthase (V), respectively. Two additional subpopulations of retrogradely traced neurons were distinct from these groups: neurofilament-immunoreactive neurons (VI), and cell bodies that were nonreactive to either of the antisera applied (VII). Nerve fibers in the adrenal medulla and cortex were equipped with the mediator combinations I, II, IV and VI. An additional meshwork of fibres solely labelled for nitric oxide synthase was visible in the medulla. Medullary as well as cortical fibres along endocrine tissue apparently lacked the chemical code V, while in the external cortex some fibre exhibited code III. Some intramedullary neuronal cell bodies revealed immunostaining for nitric oxide synthase, CGRP or substance P, providing an additional intrinsic adrenal innervation. Perikarya, immunolabelled for nitric oxide synthase, however, were too few to match with the large number of intramedullary nitric oxide synthase-immunoreactive fibres. A non-sensory participation is also supposed for the particularly dense intramedullary network of solely neurofilament-immunoreactive nerve fibres. The findings give evidence for a differential sensory innervation of the guinea-pig adrenal cortex and medulla. Specific sensory neuron subpopulations suggest that nervous control of adrenal functions is more complex than hitherto believed.

Adrenocortical responses in dexamethasone-treated rats with septal, preoptic and combined hypothalamic lesions.

To elucidate the role of limbic structures in the negative feedback regulation of corticoids of adrenocortical function, the effect of dexamethasone on adrenocortical responses to ether stress was studied in intact and lesioned rats. In animals with septal and preoptic lesions the degree of the feedback of dexamethasone on adrenocortical responses was similar to that in intact rats. In animals with bilateral medial forebrain bundle lesions the feedback influence was enhanced, but this was reversed by a subsequent posterior hypothalamic deafferentation, which if produced separately diminished the feedback effect. This would indicate that though the septum and preoptic area do not play a significant role in the feedback of dexamethasone, there is a mutual interaction between closely situated facilitatory and inhibitory systems in the feedback control of adrenal function.

Strain-Dependent Gonadal Effects upon the Response of Adrenal Cholesterol Esters to ACTH in C57BL/10J and DBA/2J Mice

The response of adrenal cholesterol esters to ACTH administered in vivo was studied in males, females and male castrates of the C57BL)10J and DBA/21 strains of mice. The cholesterol ester fatty acids were transmethylated and analyzed by gas-liquid chromatography. There are sex and strain differences in the response of the adrenal cholesterol esters to ACTH. Neither the male nor the female C57 mouse shows a significant depletion of total cholesterol esters upon ACTH treatment. This result argues against the utilization of adrenal cholesterol esters for corticosteroid synthesis in this strain. In the female DBA mouse cholesterol ester depletion in response to ACTH is maximal. Neither the total cholesterol ester concentration nor the concentration of any individual ester is correlated with the pattern of response of the cholesterol esters to ACTH. Among the individual cholesterol esters, cholesteryl arachidonate (C20:4) is preferentially utilized after ACTH treatment in all groups except the C57 males. In contrast, cholesteryl adrenate (C22:4), which is generally the most abundant cholesterol ester, is conserved during ACTH stimulation in all groups except the DBA females. A cyclic interconversion between adrenate and arachidonate may be physiologically important in the control of adrenal function.