EFFECTS OF GAMMA-IRRADIATION ON PLASMA TESTOSTERONE LEVELS AND HEPATIC DRUG-METABOLISM IN THE RAT

When adult male Sprague-Dawley rats were exposed to whole-body irradiation of γ rays ranging from 700 to 1000 rad, oxidative demethylation of drugs such as aminopyrine was significantly reduced. In agreement with the report of McTaggart and Wills, we have independently found that this irradiation-induced inhibition of hepatic drug metabolism was a result of blockade of testosterone synthesis or release. The plasma hormone levels in the treated animals (900 rad of γ rays) declined gradually from a normal value of 5.5±0.5 ng/ml to a minimum value of 0.9±0.4 ng/ml, which was reached in 4 to 6 days after the irradiation. It returned to normal level after the 10th day. This hormonal change caused by γ irradiation was parallel with the change in aminopyrine demethylation, thus suggesting that impairment of hepatic drug metabolism by γ rays was mainly secondary to the effect on the synthesis and/or release of male sex hormone.