Drug synergistic antifertility effect of combined administration of low-dose gossypol with steroid hormones in rats

Background Our previous studies suggested that low-dose gossypol combined with steroid hormones has a reversible antifertility role in adult male rats, and the course of treatment was shorter than that of either gossypol or steroid hormones alone. This result suggested that low-dose gossypol and steroid hormones have a drug synergistic effect on antifertility. The aim of the study was to find the target organs of the antifertility synergistic effect of the combined regimen. Methods Thirty-two adult male rats were divided into four groups randomly: group GH, rats were fed orally with gossypol acetic acid (GA, 12.5 mg·kg -1 ·d -1 ) and desogestrel (DSG, 0.125 mg·kg -1 ·d -1 )/ethinylestradiol (EE, 0.025 mg·kg -1 ·d -1 )/ testosterone undecanoate (TU, 100 mg·kg -1 ·d -1 ); group G, a single dose of GA (12.5 mg·kg -1 ·d -1 ) was given; group H, the same dosage of DSG/EE/TU as in group GH were administered; group C, rats were treated with vehicle (1% methyl cellulose) as control. Testes and epididymis were removed at 8 weeks post-treatment for evaluating their weight, volumes, volume fraction, and total volume of testicular tissue structures and the seminiferous tubule diameter using stereological assay. Sperm cell numbers and the motility of epididymal sperm were quantitated by flow cytometry and morphological methods. Results Compared with group C, spermatogenesis was normal in group G and suppressed in groups H and GH. Similar changes of testicular tissue structures and sperm number were found in groups H and GH. The decreases of epididymal sperm number and motility in group GH were greater than that of the low-dose gossypol or steroid hormones alone group. Conclusions The suppression of spermatogenesis was induced by steroid hormones in the combined regimen, and the epididymis was the target organ of low-dose gossypol. Combined use of low-dose gossypol and steroid hormones played a comprehensive antifertility role in their synergistic effect on reducing the number and motility of epididymal sperm. Chin Med J 2011;124(11):1678-1682 he contraceptive effects of gossypol was reported in China and some clinical trials showed that low-dose gossypol was efficient and well-tolerated without serious side effects including hypokalemia and irreversibility of fertility, but it needed 12–16 weeks to reach the infertility levels. 1-3 Hormonal contraceptives, such as testosterone, testosterone combined with progesterone or estrogen, suppress spermatogenesis and have effective and reversible antifertility. 4 However, the lack of satisfactory androgen formulation and the incomplete suppression of spermatogenesis within or between some population groups were the main obstacles. 5,6 Our previous studies suggested that low-dose gossypol acetic acid (GA, 12.5 mg·kg -1 ·d -1 ) with desogestrel (DSG, 0.125 mg·kg -1 ·d -1 ), ethinylestradiol (EE, 0.025 mg·kg -1 ·d -1 ), and testosterone undecanoate (TU, 100 mg·kg -1 ·d -1 ), produced the infertility within 8 weeks of treatment on adult male rats without systemic and genetic toxicities. Subsequently, low-dose gossypol alone could maintain the infertility after withdrawing the steroid hormones, and the antifertility role was reversible in rats. 7 These results provided a new approach for using the new regimen in clinical trials and a new prospect of gossypol as a potential male contraceptive. 8 Because the course of treatment of the combined regimen was shorter than that of either gossypol or steroid hormones alone, low-dose gossypol and steroid hormones must have synergistic effects on antifertility, but the details are unknown. In this study we evaluated the effects on testicular tissue restructure, sperm number, and epididymal sperm motility induced by the combination of low-dose T