[Studies on the feedback regulation of gonadotropin concentrations in male rats. (II). Partial characterization of 5 alpha-reductase in the medial basal hypothalamus and anterior pituitary gland].
To evaluate the testosterone (T) 5 alpha-reductase activity in medial basal hypothalamus (MBH) and anterior pituitary gland of the adult male rat, whole homogenate of MBH or anterior pituitary glands was incubated with 14C-T in the presence of coenzymes under various experimental conditions. Major metabolites were 5 alpha-dihydrotestosterone (DHT), 5 alpha-androstane-3 alpha (beta), 17 beta-diol(3 alpha(beta)-diol) and delta 4 androstenedione. The activity of 5 alpha-reductase was expressed as the sum of the amount of DHT and 3 alpha(beta)-diol formed after incubation. The metabolites converted from T was separated and identified by thin layer chromatography and confirmed by recrystallization. The anterior pituitary gland possessed about four times higher 5 alpha-reductase activity compared with that in MBH. NADPH was essential for 5 alpha-reductase activity. They existed in microsomal fraction. They had same optimum temperature and almost same optimum pH. The Michaelis constant of the 5 alpha-reductase for T in MBH and anterior pituitary gland was 3.1 X 10(-7) M and 5.6 X 10(-7) M, respectively. These results suggest that 5 alpha-reduced metabolites of T, especially DHT have some physiologically significant roles in not only MBH but also anterior pituitary gland. Furthermore, it is noteworthy that 5 alpha-reductase in the anterior pituitary showed higher activity than that in MBH.
Noguchi
K
K
Department of Urology, Yokohama City University, School of Medicine, Japan.
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D015113:Androstane-3,17-diol / Q000378:metabolism; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D013196:Dihydrotestosterone / Q000378:metabolism; D007033:Hypothalamus, Middle / Q000201:enzymology*; D008297:Male; D010903:Pituitary Gland, Anterior / Q000201:enzymology*; D051381:Rats
D013196:Dihydrotestosterone; D015113:Androstane-3,17-diol; D000735:Androstenedione; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase