Regulation of corticotropin-releasing hormone secretion by ACTH at different times after adrenalectomy.
This study was undertaken to determine the short-loop negative feedback at the hypothalamic site after adrenalectomy (ADX), when the hypothalamic-pituitary axis was a different set-points. Rats were submitted to the experimental procedure 3 h and 1, 3 and 14 days after bilateral ADX or sham surgery under ether anesthesia by the dorsal approach. ADX rats were supplied with 1.5% NaCl. After decapitation, plasma samples were collected and corticosterone (B) and adrenocorticotrophic hormone (ACTH) concentrations were determined by radioimmunoassay (RIA). Using in vitro incubation of the median basal hypothalamus (MBH) fragment we studied the hypothalamic corticotrophin-releasing hormone (CRH) release under basal conditions and under the inhibitory effect of ACTH. Hypothalamic CRH secretion, determined by direct RIA, without extraction and reported as pg CRH/MBH per 1 h incubation, was inhibited by ACTH administration in a dose-dependent manner, as demonstrated by a significant negative correlation obtained by linear regression analysis of CRH secretion as a function of ACTH dose. However, the percentage of inhibition of CRH secretion was higher at 1 and 3 days than at 14 days after ADX. In conclusion, these in vitro studies demonstrated that ACTH suppressed basal CRH secretion in a dose-dependent manner, an effect compatible with a short-loop feedback mechanism. Furthermore, we demonstrated variable suppressibility of CRH secretion by ACTH at different times after ADX.
Castro
M
M
Departamento de Clínica Médica, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brasil.
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D000315:Adrenalectomy; D000324:Adrenocorticotropic Hormone / Q000502:physiology*; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism*; D005938:Glucocorticoids / Q000502:physiology; D007031:Hypothalamus / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D005938:Glucocorticoids; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone