Differential effects of epidermal growth factor on the differentiation of type A spermatogonia in adult mouse cryptorchid testes in vitro.

The effect of epidermal growth factor (EGF) on testicular germ cell differentiation was investigated. Testicular fragments from surgically prepared cryptorchid testes of adult mice were cultured for 9 days in serum-free media containing various concentrations of EGF. Histological sections of testis were examined under a light microscope and each type of germ cell and mitotic cell in the seminiferous tubules was counted per 1000 Sertoli cells. EGF at concentrations ranging from 100 to 200 ng/ml induced differentiation of type A spermatogonia. The observed maximal stimulatory activity of EGF at a concentration of 100 ng/ml was 30% of the positive control cultures treated with calf serum. EGF at concentrations ranging from 1 to 100 ng/ml significantly inhibited the mitotic activity of FSH, FSH plus retinol, or FSH plus fetuin on type A spermatogonia and their differentiation. The number of type A spermatogonia in testes cultured with FSH, FSH plus retinol, or FSH plus fetuin decreased when EGF was added. On the other hand, EGF stimulated the differentiation of type A spermatogonia induced with fetuin but did not influence retinol-induced differentiation. It is proposed that EGF inhibits testicular germ cell differentiation by blocking the proliferation of type A spermatogonia stimulated by FSH.