Effect of phenobarbital on in vitro aromatization of testosterone to estradiol by adult male mice brain.

Adult male mice were given phenobarbital (PB) through their food containing 3.5 g/kg for 5 consecutive days. On days 3 and 5 of treatment and 5 days following termination of PB treatment the animals were sacrificed and the in vitro conversion of (1,2-3H)-testosterone to estradiol in the brains was measured. During PB treatment brain aromatization of testosterone was reduced by approximately 50% as compared to the untreated group. Five days after termination of PB administration, brain aromatase activity was as in the control group. Direct addition of PB to brain homogenates (200 micrograms/ml) reduced the conversion of testosterone to estradiol by approximately 30%. These results demonstrate that PB can act directly upon brain tissue to inhibit aromatase activity. It is assumed that this effect of PB is one of the mechanisms by which this drug inhibits testosterone action.