Hypothalamic 5α-reductase and 3α-oxidoreductase activity in the male rat

Abstract The aim of the present study was to assess the progesterone (Pr) transforming 5α-reductase (5α-R) and 3α-oxidoreductase (3α-OR) activities in the hypothalamus of the male rat as a function of age and following castration and/or adrenalectomy performed at the sixth day of life. The hypothalamic activity of these enzymes was estimated from the sum of the 5α- or 3α-reduced metabolites produced from 14 C-labeled Pr incubated “in vitro” with hypothalamic tissue. Plasma levels of testosterone (T), progesterone (Pr), estrone (E1), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured simultaneously. Special attention was paid to the GC/MS analysis of the endogenous content of the hypothalamic Pr-metabolites 3α-hydroxy-pregn-4-en-20-one (3α-Pr), 5α-pregnane-3,20-dione (5α-Pr) and 3α-hydroxy-5α-pregnan-20-one (5α,3α-Pr). The high 5α-R and 3α-OR activities estimated in the hypothalamus of prepubertal rats are not related to the action of gonadal or adrenal steroids. Substantial and comparable endogenous 3α- and/or 5α-Pr-metabolites were found in hypothalami from both prepubertal and mature rats. The results of the present study do not provide evidence for a contributory role of the 3α-hydroxylated Pr derivative to the regulation of gonadotropin secretion in the male rat.