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3 beta-Hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) catalyses an essential step in the biosynthesis of steroid hormones and is widely distributed in peripheral steroid target organs. The present report describes for first time the expression of this enzyme in the pituitary of female rats. Immunohistochemistry at the light microscopic level was performed on pro-oestrous and ovariectomized rat pituitaries. Immunoreactive cells were scattered and randomly distributed throughout the anterior lobe, whereas cells located in the posterior lobe and pars intermedia were immunonegative. Differences were observed in cell morphology and in the number of 3 beta-HSD-immunopositive cells between ovariectomized and pro-oestrous female rat pituitaries, suggesting that steroidogenic activity is affected by ovarian endocrine function. Apart from adenohypophyseal immunoreactive cells, 3 beta-HSD immunopositivity was also noted in endothelial cells of almost all pituitary capillaries located in the anterior and posterior lobes.
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Amidated forms of the peptide hormone gastrin act via the cholecystokinin-2 receptor to stimulate gastric acid secretion, whereas non-amidated forms stimulate colonic mucosal proliferation via a novel, as yet uncharacterised, receptor. Nuclear magnetic resonance (NMR) and fluorescence spectroscopic studies have revealed that glycine-extended gastrin17 bound two ferric ions, and that ferric ion binding was essential for biological activity. We have therefore investigated the role of ferric ions in the biological activity of amidated gastrin17. As with glycine-extended gastrin17, fluorescence quenching experiments indicated that Glu7 Ala and Glu8,9 Ala mutants of amidated gastrin17 each bound only one ferric ion. The affinity of the mutant peptides for the cholecystokinin-2 receptor on transfected COS-7 cells or on Tlymphoblastoid Jurkat cells, and their potency in stimulation of proliferation in Jurkat cells and inositol phosphate production in transfected COS-7 cells, were similar to the values obtained for amidated gastrin17. In addition, the iron chelator desferrioxamine did not significantly inhibit either binding of amidated gastrin17 to the cholecystokinin-2 receptor, or stimulation of inositol phosphate production by amidated gastrin17 in transfected COS-7 cells. We conclude that, in contrast to glycine-extended gastrin17, binding of ferric ions is not essential for the biological activity of amidated gastrin17. Our results support the concept of distinct modes of action for amidated and non-amidated gastrins, and raise the possibility of developing selective antagonists of the actions of non-amidated and amidated gastrins.
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ABSTRACT
We report the light microscopic, transmission and scanning electron microscopic features of the adrenal cortices in rats bearing a medullary thyroid carcinoma cell line transfected with a corticotrophin-releasing hormone (CRH) cDNA expression vector. The animals had elevated CRH, ACTH and corticosterone blood levels, involuted thymuses and markedly enlarged adrenal glands with prominent lipid-depleted cortices and dilated congested capillaries, similar to those of animals treated with ACTH. Using electron microscopy it was found that the enlarged fasciculata and reticularis zones were composed of large, compact cells with abundant smooth endoplasmic reticulum, prominent Golgi complexes, increased number of large mitochondria with focal loss of cristae and cavitation of the internal compartments, numerous lysosomes and prominent elongated microvilli. In addition, small cytoplasmic fragments were seen within the capillary lumina; these structures resembled microvilli that were apparently detached from adrenocortical cells and entered the blood stream via discontinuous endothelium of dilated capillaries. By scanning electron microscopy it was found that the cells had bulging surfaces with scattered pits and numerous long microvilli pointing in different directions.
This animal model allows analysis of the effects of protracted CRH excess resembling tumoural CRH-dependent Cushing's syndrome in human patients. Our findings call attention to the role of microvilli in adrenocortical secretion. The increased number and size of microvilli has been thought to lead to an increase in the surface area of adrenocortical cells, thereby facilitating hormone discharge. The detachment of microvilli from adrenocortical cells may represent a form of apocrine secretion and may contribute to hypercorticosteronaemia in CRH excess.
Journal of Endocrinology (1992) 135, 271–277
Search for other papers by C S Kovacs in
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Abstract
Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) share 68% homology and function as neurotransmitters or neuroendocrine factors. Although VIP immunoreactivity has been detected in bone cells, the presence of PACAP or PACAP receptors in bone has not been determined. In this study, we investigated the role of PACAP and VIP in regulating cAMP accumulation in the UMR 106 osteoblast-like tumor cell line.
PACAP 27 (10−9 to 3 × 10−7 m), PACAP 38 (10−9 to 3 × 10−7 m) and VIP (10−8 to 10−6 m) stimulated cAMP accumulation up to eightfold. PACAP 27 was slightly more potent than PACAP 38, and both were tenfold more potent than VIP. Both PACAP- and VIP-stimulated cAMP accumulation were potentiated by 4β-phorbol 12-myristate 13-acetate, an activator of protein kinase C. Two PACAP antagonists, PACAP 6–27 (3 × 10−6 m) and PACAP 6–38 (3 × 10−6 m), blocked PACAP- and VIP-stimulated cAMP accumulation. Two VIP antagonists ([Lys1,Pro2,5,Arg3,4,Tyr6]-VIP, and 4 Cl-d-Phe6,Leu17]-VIP) did not reduce the PACAP-or VIP-stimulated cAMP accumulation. Pretreatment with PACAP 27, PACAP 38 or VIP equally blocked PACAP- and VIP-stimulated cAMP accumulation.
These results suggest that PACAP is a more potent stimulator of cAMP accumulation than VIP in UMR 106 cells. PACAP and VIP may share a role in the paracrine or neuroendocrine regulation of bone metabolism.
Journal of Endocrinology (1996) 149, 287–295
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ABSTRACT
Stimulation of the immune system or experimental conditions (bacterial lipopolysaccharide (LPS) treatment) provoke a broad spectrum of physiological responses. It was recently shown that one of them is the activation of the hypothalamic-pituitary-adrenal (HPA) axis. The mechanism and the site or sites through which LPS stimulates the HPA axis are not well understood.
To establish whether the effect of bacterial LPS is related in vivo to the presence of hypothalamic hypophysiotrophic peptides (corticotrophin-releasing factor-41, arginine vasopressin, etc.), plasma ACTH and corticosterone levels were monitored in intact and sham-operated rats, and in rats with paraventricular nucleus lesions in order to remove the main source of these neuropeptides. Evidence was obtained that 4 h after treatment, LPS was able to activate the hypophysial-adrenal system in the absence of hypophysiotrophic neuropeptides of paraventricular origin.
It is suggested that, in vivo, LPS could have a direct effect on the pituitary gland or that it acts through an extrapituitary, non-paraventricular pathway to activate the HPA axis.
Journal of Endocrinology (1992) 133, 231–236
