Aromatase activity in the perinatal rat forebrain: effects of age, sex and intrauterine position.

Sex and regional differences in aromatase activity were characterized in brains of rats sacrificed on embryonic days 18 (E18) and 20 (E20) and on postnatal days 2, 4 and 13 (D2, D4, D13). Aromatase activity was measured in vitro in homogenates of the hypothalamus/preoptic area (HPOA) and temporal lobe (TL) from individual rats, using [3H]19-hydroxyandrostenedione as substrate in the presence of NADPH. The apparent Km of aromatase for 19-hydroxyandrostenedione in TL at D4 was similar in males (34 nM) and females (22 nM,). Aromatase activity in the HPOA was highest prenatally (E18) and gradually declined to low levels by D13. Aromatase activity in the TL remained constant from E18 to D2, increased significantly on D4, and subsequently declined to low levels by D13. The level of aromatase activity was significantly greater in males than in females on E18 and D4 in the HPOA and on D4 in the TL. Differences in aromatase activity within regions of the HPOA were studied at E20 and D4. At both ages, the activity was highest in the preoptic area, lower in the anterior hypothalamus (AH), and lowest in the posterior hypothalamus. Aromatase activity was significantly higher in males than in females in the AH, but only on D4. The contiguity of males in utero was not correlated with aromatase activity in brain regions of adjacent female fetuses. The present results indicate that significant sex differences in aromatase activity exist in specific brain regions only at discrete times during perinatal development.(ABSTRACT TRUNCATED AT 250 WORDS)