Rat liver cytosolic alcohol dehydrogenase (ADH) is the principal enzyme which catalyzes the oxidation of ethanol. ADH activity is known to be significantly higher in females than in males. However, the precise mechanism of the sex-difference in ADH activ ity is uncertain. Recently, we have shown that the inhibitory action of androgen and the slight facilitatory actions of progestin and estrogen are involved in the mechanism of sex-dif ference in adult rat liver ADH activity. In the present

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... , we studied the difference of the postnatal developmental changes of ADH activity between males and females. ADH activity increased rapidly after birth up to about 12d of age, and was not different in the two sexes. In female rats, ADH activity peaked at about 30d of age and then increased gradually to plateau levels. However, the ADH activity of male rats fell markedly between 30 and 45d old, and the reduced enzyme activity was observed until 104d old. In conclusion, the ADH activity of male rats fell between 30 and 45d after birth. At the ages over the turning point, the ADH activity was significantly lower in male than in female rats.