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PARACRINE REGULATION OF SPERMATOGENESIS BY GROWTH FACTORS

We have established a testis tissue culture model which enables studies of the effects of growth factors on germ cell proliferation in vitro. Segments of seminiferous tubules of adult rat testes representing defined stages of the seminiferous epithelial cycle with representative premitotic and premeiotic germ cells were identified by transillumination and prepared by microdissection. The tubule segments were incubated at 34°and 37°C for 24, 48, and 72 h with and without growth factors and the DNA synthesis was determined at the end of the incubation. Recombinant epidermal growth factor (EGF) was found to stimulate premeiotic DNA synthesis in a dose-dependent fashion whereas premitotic DNA synthesis was only slightly affected. This indicates that EGF is mainly a meitotic growth factor during spermatogenesis. Together with previous results demonstrating specific effects of interleukin-1α, nerve growth factor and insulin-like growth factors, the present finding form the basis of a hypothesis that mitotic and meiotic proliferation of germ cells is differentially regulated by locally produced growth factors acting in a paracrine fashion.