Effect of testosterone enanthate on follicular growth in rats

The effects of exogenous testosterone enanthate, a long-acting testosterone ester, on estrous activity and reproductive performance in female rats were studied. An injection of 2.5-20.0 mg of testosterone enanthate delayed until 26.9-60.1 days the cycling of the estrous cycle in a dose-dependent way; the treated rats began regular 4-day estrous cycles 41.9-80.7 days after the injection. Subsequent reproductive performance was not different in the treated and control animals (P>.05). Ovarian weight during estrous inhibition decreased steadily after treatment, but the uterine weight increased for a time. The ovaries contained follicles and interstitial cell islands, but no new ovulatory corpora lutea, The injection decreased the number of small follicles (250-549 mu m), but increased the number of mature large follicles (greater than or equal to 550 mu m; P<.05). The mean testosterone concentration in the peripheral plasma during estrous inhibition was higher than that before the treatment (P<.05). Testosterone concentrations increased for a time after treatment (P<.05), but decreased steadily thereafter. These results suggest that testosterone enanthate might be used for long-term contraception; the effects seem to depend on testosterone. Continuous stimulation by the long-term activity of testosterone inhibited the growth of small follicles but stimulated the growth of large follicles. (C) 1996 Wiley-Liss, Inc.