| Abstract: | Maturation of bovine oocyte-cumulus complexes (OCC) in media derived following granulosa cell culturing with prolactin (PRL, 50 ng/ml) and somatotropin (ST, 10 ng/ml) was studied. A medium conditioned by granulosa cells in the presence of PRL or ST exerted a stimulating effect on the proliferative activity of cumulus cells. ST introduction into the granulosa cell culture also caused a decrease in the rate of cumulus cells with degenerated chromatin at a subsequent OCC culturing. At the same time, the expansion of cumulus did not depend on hormone availability in the culture medium for granulosa cells. When OCC matured in conditioned media, a short-term inhibition of oocyte meiosis reinitiation (after 6 h of culturing) was revealed in both the experimental groups, as compared to the control. Furthermore, the addition of ST and PRL to granulosa cell culture resulted in a subsequent decline in the rate of oocytes with signs of chromosome degeneration, observed as early as by 6 h of incubation and to be retained throughout the whole period of OCC culturing. In this case the earlier resumption of meiosis was associated with a higher rate of degeneration of the nuclear material in oocytes. The results of the present study suggest that granulosa cells may mediate, at least in part, PRL and ST impacts on in vitro maturation of bovine OCC, with no contact between OCC and granulosa cells being required for hormonal signaling. |
