Effect of acute and prolonged mineralocorticoid receptor blockade on spontaneous and stimulated hypothalamic-pituitary-adrenal axis in humans.
ABSTRACT Mineralocorticoid receptors (MRs) in the hippocampus display an important role in the control of the hypothalamic-pituitary-adrenal (HPA) axis, mediating the proactive feedback of glucocorticoids, which maintains the basal HPA activity. The systemic administration of MR antagonists enhances spontaneous and CRH-stimulated ACTH, cortisol, and DHEA secretion, while the effects of chronic treatment with MR antagonists are scanty. Our study was performed in order to clarify this point.
ACTH, cortisol, and DHEA levels were studied during the infusion of placebo, canrenoate, a MR antagonist (CAN, 200 mg i.v. bolus at 1600 h followed by 200 mg infused over 4 h), and human CRH (hCRH; 2.0 microg/kg i.v. bolus at 1800 h) before and during the last week of 28-day treatment with CAN (200 mg/day p.o.) in eight young women.
Pre-treatment sessions: CAN and hCRH administration increased ACTH, cortisol, and DHEA levels versus placebo (P<0.05). Post-treatment sessions: during placebo infusion, cortisol and DHEA were significantly amplified versus pre-treatment session (P<0.05), while ACTH levels were not modified; CAN infusion, differently from pre-treatment session, was not able to significantly increase ACTH, cortisol, and DHEA levels; ACTH, cortisol, and DHEA responses to hCRH were amplified with respect to pre-treatment session, although statistical significance was obtained for cortisol and DHEA only.
MR blockade by acute CAN administration significantly enhances the HPA activity in the afternoon, during the quiescent phase of the circadian rhythm. At the same period, prolonged treatment with CAN amplifies both spontaneous and CRH-stimulated activities of the HPA axis, while it blunts the HPA responsiveness to a further MR-mediated stimulation.
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ABSTRACT: This clinical review will summarize the available data regarding the role of mineralocorticoid receptors (MRs) on the hypothalamus-pituitary-adrenal (HPA) axis control in physiological and pathological conditions and in the memory processes involved in the control and appraisal of a stress event. MRs are predominantly expressed in the limbic structures, with the hippocampus being the main localization, although MRs are also found at the hypothalamic level. It is known that hyppocampal MRs control the proactive feedback involved in the maintenance of the basal HPA activity, mainly at the nadir of the circadian rhythm. In physiological conditions, the administration of pharmacological doses of both MR antagonists and agonists is able to interact with the HPA activity, modifying the quiescent phase-nadir of the circadian rhythm, although some data in the literature do not support these observations. Also, in a physiological condition such as aging, an enhanced HPA axis activity is found in the time window, when MRs are predominantly occupied by cortisol circulating levels, possibly reflecting an MR impairment in this period of life. In pathology, major depression has been correlated to MR qualitative-quantitative alterations which could reflect differences on psychological and physiological responses, possibly predicting psychopathologies. Most of the remarks reported in this review seem to indicate, in agreement with animal data, a role played by MRs in the delicate control of the HPA axis in humans and the possible predisposition to the development of pathologies in case of their alterations.Endocrine 07/2012; · 3.53 Impact Factor
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ABSTRACT: Mineralocorticoid receptors (MR) in the hippocampus display an important role in the control of hypothalamic-pituitary-adrenal (HPA)-axis, mediating the "proactive"-feedback of glucocorticoids. Fludrocortisone (FC), a potent MR agonist, has been shown to decrease HPA activity through a mechanism placed at hippocampal level. In order to clarify the effects of MR agonism on HPA function in humans, we studied the effects of FC, in a dose-related manner, on both basal and CRH-stimulated HPA axis during the quiescent phase. 8 young women were studied. ACTH, cortisol and aldosterone levels were evaluated every 15', from 1600 to 2000 hours, in randomized sessions: (1) placebo p.o. + placebo i.v., (2) 0.3 mg FC p.o. + placebo, (3) 0.1 mg FC. + placebo, (4) 0.075 mg FC + placebo, (5) 0.05 mg FC + placebo, (6) placebo + hCRH (2.0 μg/kg iv-bolus), (7) 0.3 mg FC + hCRH, (8) 0.1 mg FC + hCRH, (9) 0.075 mg FC + hCRH, (10) 0.05 mg FC + hCRH. FC induced a dose-related trend toward a further decrease of the ACTH and cortisol levels, while it showed a significant and dose-dependent inhibition of the hormonal response to hCRH (p < 0.05 for the doses of 0.3, 0.1 and 0.075 mg). Conversely, 0.05 mg FC did not modify the CRH-stimulatory effect on both ACTH and cortisol secretion. Aldosterone levels were not modified by FC administration. Fludrocortisone inhibits corticotrope and adrenal response to hCRH in humans, in a dose-dependent manner. The 0.075 mg FC seems the lowest active while 0.05 mg the first neutral dose on HPA activity. These data suggest a possible hypophysial MR-mediated inhibiting effect of FC, although its pituitary glucocorticoid-mediated effect cannot be excluded. The interplay between fludrocortisone and hypophysial glucocorticoid receptors needs to be clarified in order to define better the clinical consequences of the hormonal replacement therapy of patients with primary adrenal insufficiency.Pituitary 09/2012; · 2.22 Impact Factor
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ABSTRACT: In both mammals and teleost fish, serotonin stimulates cortisol secretion via the 5-HT(1A) receptor. Additionally, a negative feedback loop exists in mammals whereby increased circulating levels of cortisol inhibit 5-HT(1A) receptor activity. To investigate the possibility of such a feedback mechanism in teleosts, plasma cortisol levels and signaling in Gulf toadfish (Opsanus beta) were manipulated and the role of cortisol in the control of 5-HT(1A) evaluated. Despite a significant 4-fold increase in plasma [cortisol], crowded toadfish expressed similar amounts of 5-HT(1A) mRNA transcript as uncrowded toadfish; whereas, cortisol-implanted fish possessed 41.8% less 5-HT(1A) mRNA transcript compared to vehicle-implanted controls. This cortisol effect appeared to be reversed in RU486-injected fish, which blocks glucocorticoid receptors, as these fish expressed nearly twice as much 5-HT(1A) receptor transcript as the vehicle-injected fish despite significantly elevated cortisol levels. The binding affinity for the 5-HT(1A) receptor in the brain did not vary between any groups; however, maximum binding was significantly higher in uncrowded toadfish compared to crowded, and the same significant difference was observed between the maximum binding of vehicle and cortisol-implanted fish. The opposite trend was seen in RU486-injected and vehicle-injected fish, with RU486-injected fish having significantly higher maximal binding compared to vehicle-injected controls. Injection with the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin revealed an inhibition of cortisol secretion that was independent of 5-HT(1A) transcript and protein binding. These results suggest that cortisol plays a role in regulating the 5-HT(1A) receptor via GR-mediated pathways; however, further study is necessary to elucidate how and where this inhibition is mediated.Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 01/2013; · 2.20 Impact Factor