FSH suppression of nitric oxide synthesis in porcine oocytes

The present study was designed to evaluate the regulation of nitric oxide ( NO) synthesis in porcine oocytes during follicular development. Cumulus-ooc yte complexes were obtained by aspirating the small follicles of immature p orcine ovaries and cultured at 39 degrees C for 24-72 h with FSH in a serum -free medium. The oocyte-surrounding cumulus cells markedly proliferated an d expressed LH receptor mRNA in response to FSH. The endothelial type of NO synthase (eNOS) (130 kDa) was detected in the oocyte, but not in the proli ferated cumulus cells, by immunoblotting. The amount of oocyte eNOS did not significantly alter during culture, but measurement of nitrite and nitrate revealed FSH suppression of NO synthesis by approximately 50%. NO-releasin g agents were added to the cultures to examine the effect of NO on the grow th of cumulus cells. NO-releasing agents showed inhibitory effects on proli feration of the cumulus cells and expression of LH receptor mRNA. Thus, syn thesis of eNOS-derived NO is suppressed in the porcine oocyte during develo pment with no change in the enzyme amount, and it is suggested that it has an inhibitory function in the growth of cumulus cells.