THYROTROPIN-RELEASING-HORMONE INHIBITS GLUCOCORTICOID SECRETION OF RAT ADRENAL-CORTEX - IN-VIVO AND IN-VITRO STUDIES

The bolus iv administration of TRH dose-dependently decreased ACTH-enh anced plasma corticosterone (B) concentration in rats, without affecti ng the basal one. The effects of TRH on steroid secretion of dispersed rat inner adrenocortical cells were investigated by HPLC. TRH signifi cantly decreased both basal and ACTH-stimulated post-11-deoxycorticost erone (DOC) secretion (i.e. 18-hydroxy-DOC and B) and concomitantly ra ised DOC and progesterone release, so that the total postpregnenolone yield of our preparations was unaffected. TRH did not alter either bas al or ACTH-stimulated pregnenolone production by isolated rat adrenoco rtical cells. It was concluded that TRH is an inhibitor of glucocortic oid secretion in rats, which electively impairs the late steps of B sy nthesis (i.e. 11- and 18-hydroxylation) without affecting the earlier steps, including the rate-limiting one of this process.