The effect of prolactin on DNA synthesis in cultured bovine granulosa cells
Lebedeva, I.Iu.; Kuz'mina, T.I.; Goĭlo, T.A.
Tsitologiia 37(3): 220-226
1995
ISSN/ISBN: 0041-3771 PMID: 8553460 Document Number: 439613
The influence of bovine prolactin (bPRL) on DNA synthesis in bovine granulosa cells cultured in various media was studied. bPRL exerted a mitogenic effect on granulosa cells from follicles with diameters of 3-5 mm, with the effect depending on the hormone concentration of culture medium. The maximum effective concentration of bPRL was 100 times higher in the medium containing bovine somatotropin than in other media used. The extent to which bPRL influenced the proliferation of granulosa cells depended on the degree of cell differentiation. In cultures of granulosa cells from follicles which were 1-2 or 3-5 mm in diameter, stimulation of DNA synthesis decreased as the bPRL concentration increased from 500 ng/ml to 5 micro g/ml (in serum-free medium) and from 50 to 500 ng/ml (in medium containing 5% bovine foetal serum). The growth-stimulating effect of bPRL on granulosa cells from 6-10 mm follicles was not affected by the concentration of bPRL in the culture medium. The maximum mitogenic effect decreased as follicles grew, in line with the hypothesis that proliferation of granulosa cells decreases progressively during follicular maturation. It is suggested that the mitogenic effect of bPRL on bovine granulosa cells is mediated by a somatomedin (e.g. insulin-like growth factor). PRL may stimulate the synthesis by granulosa cells of a substance which inhibits DNA synthesis; the ability to secrete this substance may be lost during the process of differentiation of granulosa cells, explaining why the growth-stimulating effect of bPRL on granulosa cells from follicles of 6-10 mm diameter does not change as the hormone concentration increases. The entry of bPRL into culture cells stimulates the synthesis of an inhibitor of oocyte maturation (IOM) in the cells; granulosa cells from follicles with small diameters secrete IOM more actively than cells from larger follicles. It is also suggested that bPRL acts on the follicle through lactogenic receptors situated on the plasma membrane of granulosa cells.