Central actions of glucocorticoids in the control of body fluid homeostasis: Review

S.G Ruginsk,L.L.K Elias,A Lopes Da Silva,J Antunes-Rodrigues,R.R Ventura

doi:10.1590/s0100-879x2009000100010

Abstract

The involvement of the hypothalamic-pituitary-adrenal axis in the control of body fluid homeostasis has been extensively investigated in the past few years. In the present study, we reviewed the recent results obtained using different approaches to investigate the effects of glucocorticoids on the mechanisms of oxytocin and vasopressin synthesis and secretion in response to acute and chronic plasma volume and osmolality changes. The data presented here suggest that glucocorticoids are not only involved in the mechanisms underlying the fast release but also in the transcriptional events that lead to decreased synthesis and secretion of these neuropeptides, particularly oxytocin, under diverse experimental conditions of altered fluid volume and tonicity. The endocannabinoid system, through its effects on glutamatergic neurotransmission within the hypothalamus and the nuclear factor kappaB-mediated transcriptional activity, seems to be also involved in the specific mechanisms by which glucocorticoids exert their central effects on neurohypophyseal hormone synthesis and secretion.

Highlights

The control of body fluid homeostasis involves complex mechanisms that regulate water and electrolyte ingestion and excretion
Co-localization of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) was observed in the parvocellular region, but not in the magnocellular region of the PVN [30]. These results suggest that MR and GR may interact in the control of HPA axis activity
Results obtained in our laboratory indicate that there is an increase in total glutamate content in the PVN and SON of rats submitted to blood volume expansion (BVE) and this response is not altered by dexamethasone pre-treatment, suggesting that the balance between neurotransmitter production and release would not be affected in this condition [47]

Summary

Introduction

The control of body fluid homeostasis involves complex mechanisms that regulate water and electrolyte ingestion and excretion. Ent on the integrity of the third ventricle anteroventral region, which comprises the organum vasculosum of lamina terminalis, the ventral portion of the median preoptic nucleus (MnPO) and the subfornical organ (SFO) These structures, once stimulated, can determine responses that involve 1) the behavioral induction of thirst or salt appetite, or both, 2) changes in sympathetic and renal nerve activity, 3) activation of the renin-angiotensin-aldosterone system, or 4) secretion of AVP and OT from the neurohypophysis, and 5) secretion of natriuretic peptides from the heart. It has been demonstrated that pre-treatment with an OT receptor antagonist increases NaCl intake induced by intracerebroventricular injection of ANG II, without significant changes in water intake, suggesting an inhibitory action of OT on salt appetite [12] Taken together, these data provided a link between the central mechanisms controlling body fluid homeostasis and the peripheral adjustments of renal and cardiovascular systems in response to acute increases in plasma volume and osmolality. Tissuespecific glucorticoid metabolism may be involved in the control of fluid balance and blood pressure

Effects of glucocorticoids on neurohypophyseal hormone secretion

Effects of glucocorticoids on hypothalamic neuronal activation

Discussion

Findings

Decreased hormone synthesis