Studies on oestrogen-2/4-hydroxylase activity in mammalian brain, using a radioenzymatic assay method

The activity of oestrogen-2/4-hydroxylase in brain tissue was studied using a radioenzymatic assay which controlled for non-specific formation of catechol oestrogen. The ontogeny of enzyme activity in male and female rat brain was examined between 1 and 70 days of age. Until 10 days of age, both sexes showed low enzyme activity. Between days 10 and 15 enzyme activity in the female significantly increased but was unchanged in the male. Male brain enzyme activity increased between days 15 and 20 whereas activity was unchanged in the female. Both males and females showed increases in enzyme activity between 20 and 25 days of age. Thereafter enzyme activity plateaued but at all ages between day 20 and day 70 male brain enzyme activity was significantly greater than in the female. A study of the distribution of the oestrogen-2/4-hydrolase in the sheep hypothalamus revealed that the stalk/median eminence had approx 10 times greater activity than either the anterior, medial or posterior hypothalamus. These findings are discussed in relation to sexual differentiation of the brain.