[The effect of prolactin on DNA synthesis in cultured bovine granulosa cells]

The influence of bovine prolactin (BPL) on DNA synthesis in cultured cow granulosa cells in various media has been studied. BPL exerted a mitogenic effect on granulosa cells of follicles 3-5 mm in diameter, with the effect depending on hormone concentration in the cultural medium. In the medium with bovine growth hormone the maximum effective concentration of BPL was 100 times more than in other used media. The degree of BPL influence on granulosa cell proliferation depended on the degree of cell differentiation. In cultures of granulosa cells taken from follicles 1-2 and 3-5 mm in diameter, while the BPL concentration increased from 500 ng/ml to 5 micrograms/ml in the serum free medium, and from 50 ng/ml to 500 ng/ml in the medium with 5% fetal bovine serum, the stimulation of DNA synthesis in cells decreased. The growth-promoting influence of BPL on granulosa cells of follicles 6-10 mm in diameter did not depend on its concentration in the cultural medium. The maximum mitogenic hormonal effect decreased with the growth of a follicle. This fact is in accord with the recent notions of a progressive reduction of granulosa cell proliferative activity during follicular maturation. The results obtained are discussed in terms of a hypothesis that prolactin can influence granulosa cell secretion of a regulator of meiosis and folliculogenesis, i.e. an inhibitor of oocyte maturation.