ABSTRACT
1. An assay using [14 C-methyl]-S-adenosyl-L-methionine was used to measure catecholamine-O-methyl-transferase (COMT) activity in the hypothalamus of newborn male and female rats from day 1 to day 12 and in adult animals after day 60. 2. There was no difference in COMT activity between sexes until day 8, when it became significantly higher in females. 3. Administration of 200 microng testosterone propionate to female rats at birth reduced the hypothalamic COMT level of the adult to that observed for male littermates. The response was dose-dependent in the range 50 to 200 microng. The hypothalamic contnet of COMT after puberty of male rats castrated ar birth was comparable to that of post-pubertal females. 4. These results show that COMT, one of the enzymes involved in the control of brain biogenic amines, is also affected by the process of sexual differentiation of the brain