Daily subcutaneous injections of 50:-androstane-3a,17,8-diol (50:-A-diol), testosterone or combination of both hormones into testectomized mice caused an increase in the muscletype LDH (LDH 5) activity reduced by testectomy, and induced the precocious appearance of the adult male-type distribution of LDH isozymes in developing mice. In adult mice, testectomy reduced the ratio of LDH 5 in the masseter muscle to the female level. Cyproterone acetate depressed the appearance of the male-type

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... bution of the isozymes in developing male animals. Moreover, in intact female mice, 5a-A-diol had a positive effect on shifting the isozyme distribution to the male type. In contrast, the distribution pattern of LDH isozymes in the tongue were not affected by any treatments. These results suggest that both androgenic hormones and receptors are involved in the appearance of sexual dimorphism in the masseter muscle of mice, but not in the tongue, and suggest that continuous release of androgenic hormones from the testes is needed to maintain the male type of LDH isozyme distribution.