Abstract
The present study was undertaken to examine the effect of homologous serum and follicular fluid on the maturational changes occurring in porcine oocyte-cumulus complexes cultured in vitro. In the basic medium (modified Krebs-Ringer bicarbonate medium) cumulus cell mass did not expand but 83.1% of oocytes resumed maturation division and 63.5% completed the first meiotic division after 48-54hr in culture. Resumption of maturation division was markedly inhibited by the addition of 1 or 5% porcine serum or follicular fluid to the basic medium. By contrast, adding porcine serum or follicular fluid to the medium containing 10i.u./ml PMSG or hCG resulted in mucification and expansion of cumulus mass and in increasing the number of oocytes reaching metaphase II. Similar results were obtained when the ultrafiltrated fraction of porcine serum or follicular fluid (molecular weight<10, 000) was added to the basic medium together with PMSG or hCG. These results suggest that both porcine serum and follicular fluid contain cumulus expanding factor and germinal vesicle breakdown-inhibiting factor and both factors have a molecular weight of less than 10, 000. It is considered that maturational changes occurring in preovulatory oocyte-cumulus complexes are induced by joint action of the component(s) in follicular fluid and gonadotrophin.
