Effects of 17β-oestradiol and 5α-dihydrotestosterone on the expression of the muscle and heart types of lactate dehydrogenase isozymes in the masseter muscle of developing mice

17β-oestradiol (E2) and/or 5α-dihydrotestosterone (5α-DHT) had no effect on the expression of isozymes of lactate dehydrogenase (LDH) in the masseter muscle of intact male mice. However, treatment with E2 restored the level of the muscle (M) type of LDH isozyme, which had been reduced by testectomy, to that found in intact male mice treated with vehicle only. Moreover, 5α-DHT alone was more effective than E2 in increasing the relative level of this isozyme in testectomized mice. 5α-DHT had a more significant effect on the increase in the relative level of the M-type LDH isozyme when combined with E2. These results suggest that androgens promote, in the presence of oestrogens, the postnatal changes in the characteristics of the masseter muscle of developing male animals.