Difference in the effects of phenobarbital and 3-methylcholanthrene treatment on subunit composition of hepatic glutathione S-transferase in male and female rats.

Male rats more than seven weeks old showed significantly higher activity of hepatic cytosolic glutathione S-transferase (GST) than females. This sex-related difference in GST activities might be explained by the difference in subunit composition of the enzymes between males and females. The relative proportion of subunit composition of GST between adult male and female rats was as follows: Ya, female greater than male; Yb(Yb'), male much greater than female; Yc, female greater than male. Since phenobarbital (60 mg/kg, i.p. for seven days) induced the Yb subunit as well as Ya subunit, the enzyme activity was more increased in males than in females and the sex difference became more marked. 3-Methylcholanthrene (20 mg/kg, i.p. three times) caused an increase of Ya subunit alone, and then the increased extent was greater in females than in males, and resulted in the disappearance of sex difference.