Regulation of Brain Aromatase Activity in Rats*

Abstract

The distribution and regulation of aromatase activity in the adult rat brain with a sensitive in vitro assay that measures the amount of 3H2O formed during the conversion of [1.beta.-3H]androstenedione to estrone. The rate of aromatase activity in the hypothalamus-preoptic area (HPOA) was linear with time up to 1 h, and with tissue concentrations up to 5 mgeq/200 .mu.l incubation mixture. The enzyme demonstrated a pH optimum of 7.4 and an apparent Km of 0.04 .mu.M. The greatest amount of aromatase activity was found in amygdala and HPOA from intact male rats. The hippocampus, midbrain tegmentum, cerebral cortex, cerebellum and anterior pituitary all contained negligible enzymatic activity. Castration produced a significant decrease in aromatase activity in the HPOA (P < 0.001), but not in the amygdala or cerebral cortex (P < 0.05). The HPOA of male rats contained significantly greater aromatase activity than the HPOA of female rats. In females, this enzyme activity did not change during the estrous cycle or after ovariectomy. Administration of testosterone to gonadectomized male and female rats significantly enhanced HPOA aromatase activities (P < 0.05) to levels approximating those found in HPOA from intact males. Apparently testosterone, or one of its metabolites, is a major steroidal regulator of HPOA aromatase activity in rats.