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The biological mechanisms that determine cell-specific responses to glucocorticoid hormones may overlap with those that are associated with acquired glucocorticoid resistance. Cell and tIssue specificity can be brought about in many different ways. Studies on the brain, an important glucocorticoid target tIssue, may provide examples of regulatory mechanisms underlying response specificity at multiple levels. In this commentary a number of such mechanisms are discussed, with emphasis on regulation of glucocorticoid bio-availability by the efflux transporter P-glycoprotein and on the variable presence of nuclear proteins which modulate or interfere with gluco- and mineralocorticoid receptor-mediated transcription.
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In fibroblasts derived from human adipose tissue, aromatase induction is observed after exposure to 1 microM cortisol in the presence of serum or platelet-derived growth factor (PDGF). Progesterone suppresses this induction in a dose-dependent manner, 10 microM resulting in complete inhibition. A reduced cortisol concentration (0.1 microM) concomitantly reduces the progesterone concentration required for effective inhibition (10-100 nM). This effect of progesterone is specific, as neither the release of cellular enzymes nor aromatase induction by dibutyryl-cAMP, which acts independently from cortisol, are affected. However, the inhibitory effect of progesterone requires its presence throughout the induction period. Kinetic studies in intact cells reveal a reduced number of aromatase active sites upon progesterone treatment, whereas progesterone at near-physiological concentration (100 nM) does not inhibit aromatase activity in isolated microsomes. Semi-quantitative reverse transcriptase PCR analysis shows reduced amounts of aromatase mRNA in progesterone-treated cells, indicating specific inhibition of the glucocorticoid-dependent pathway of aromatase induction. The inhibitory effect of progesterone is not blocked by the anti-progestin ZK114043, excluding action via progesterone receptors and indicating competition for the glucocorticoid receptor. Progesterone must be considered a potential physiological inhibitor of glucocorticoid-dependent aromatase induction in adipose tissue. It is proposed that it is a suppressor of aromatase induction in adipose tissue in premenopausal women.
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The hypothalamic-pituitary-adrenal (HPA) axis is activated during many bacterial and viral infections, resulting in an increase in circulating glucocorticoid levels. This HPA axis activation and glucocorticoid response are critical for the survival of the host, as demonstrated by the fact that removal of the HPA axis (by adrenalectomy or hypophysectomy) or glucocorticoid receptor (GR) blockade enhances the severity of the infection and in some cases enhances the mortality rate. Replacement with a synthetic glucocorticoid reverses these effects by reducing the severity of the infection and provides protection against lethal effects. In addition, some bacteria and viral infections have been shown to affect the GR directly. These have been described and the implications of such an effect discussed.
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ABSTRACT
The influence of vitamin A on the binding properties of hepatic glucocorticoid receptors (GR) was studied in young rats 7 weeks after they had been given a diet with or without vitamin A. Scatchard analysis showed an increased capacity of cytosolic GRs to bind dexamethasone in vitamin A deficiency. In these rats, an increase in tyrosine aminotransferase also occurred, and this could be related to the increased formation of hormone–GR complexes. Measurement of protein kinase C activity showed an increase which might be related to the functional activity of GRs.
Journal of Endocrinology (1992) 133, 169–173
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In vitro, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1) catalyses the interconversion of active corticosterone and inert 11-dehydrocorticosterone. 11beta-HSD-1 is highly expressed in liver, where the reaction direction is 11beta-reduction, thus potentially increasing intrahepatic active glucocorticoid levels. Inhibition of 11beta-HSD-1 increases insulin sensitivity in humans in vivo suggesting that hepatic 11beta-HSD-1 plays a role in the maintenance or control of key glucocorticoid-regulated metabolic functions. We have selectively repressed hepatic 11beta-HSD-1 in rats by oestradiol administration for 42 days. This nearly completely repressed hepatic 11beta-HSD-1 mRNA expression and enzyme activity and reduced expression of hepatic glucocorticoid-inducible genes including phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting step in gluconeogenesis. Similar effects were seen after 3 weeks of oestradiol treatment. To examine whether this was due to any direct effect of oestradiol upon PEPCK, the experiment was repeated in adrenalectomised rats+/-glucocorticoid replacement. In adrenalectomised rats, oestradiol did not attenuate hepatic PEPCK, whilst glucocorticoid replacement restored this action. Oestradiol did not alter hepatic metabolism of corticosterone by pathways other than 11beta-HSD-1. These data suggest 11beta-HSD-1 plays an important role in maintaining expression of key glucocorticoid-regulated hepatic transcripts. Enzyme inhibition may provide a useful therapeutic target for manipulating glucose homeostasis.
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whether these very early embryonic responses to cortisol were associated with the interaction of the hormone with glucocorticoid receptors (GRs; Veleiro et al . 2010 ). GRs, together with gr mRNA transcripts, are ubiquitous in the cytosol of post
Translational and Clinical Research Institute, Newcastle University, Newcastle upon Tyne, UK
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of dystrophin protein weakens the sarcolemmal membrane and results in progressive replacement of muscle fibres by fat and fibrous tissue ( Deconinck & Dan 2007 ). Glucocorticoids (GC) are currently the mainstay of treatment in DMD and are an
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Introduction Response to neuroendocrine stress begins with the activation of the hypothalamic–pituitary–adrenal (HPA) axis leading to the increase in stress hormones glucocorticoids (GCs). These hormones mediate adaptation to stress and also
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SUMMARY
1. Fresh splenic tissue from pigs was extracted by the method of Swingle & Pfiffner for adrenocortical extracts, 1 ml. being equivalent to 100 g splenic tissue.
2. The material extracted was readily soluble in ethanol, benzene, acetone and water, but not in petroleum ether. It contained no protein, bile pigments, fat, fatty acids or cholesterol, and had marked reducing properties.
3. Administration of the extract to adrenalectomized male mice caused an increase, continuous with increasing dose of extract, in the glycogen content of liver and muscle. The increase in liver glycogen produced by 1·2 ml. extract was about the same as that caused by 2 mg cortisone.
4. In intact rats the extract caused an increase in blood sugar and in the glycogen content of liver and muscle. Cortisone had a similar effect.
5. Neither the splenic extract nor cortisone raised the glycogen content of the brain in adrenalectomized mice or intact rats.
6. Thus the spleen contains a substance which has a glucocorticoid-like effect on the carbohydrate metabolism of adrenalectomized and intact animals. In view of its chemical and biological properties, this substance is thought to be a glucocorticoid originating in the adrenal cortex. A substance with similar effects has been previously detected in liver, brain and muscle.
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SUMMARY
[7-3H]Pregnenolone was incubated with homogenates of adrenal glands from two 100-day-old sheep foetuses. Cortisol and corticosterone were isolated and identified by reverse isotope dilution and recrystallization to constant specific activity. Together these two compounds accounted for 12% and 17% of the substrate with the two tissue preparations. Other C21 and C19 metabolites which were sought were not present in appreciable quantities. Additional incubations were done with the adrenals of lamb foetuses ranging in age from 110 days of gestation to the immediate newborn period. Glucocorticoidogenic capacity similar to that of the 100-day-old foetuses was demonstrated throughout this period and no age-related change was evident. These results demonstrate that the lamb foetal adrenal has a substantial enzymic capacity for glucocorticoid synthesis throughout at least the last third of gestation. In conjunction with the observations of others, these experiments support the hypothesis that during this period of gestation the lamb foetal adrenal is actively synthesizing glucocorticoids in a manner which is similar to the lamb at term and the adult sheep.
