Short time priming of pig cumulus-oocyte complexes with FSH and forskolin in the presence of hypoxanthine stimulates cumulus cells to secrete a meiosis-activating substance

This study evaluated the effect of forskolin and FSH on pig oocyte maturati on when cultured in a maturation inhibiting system. Ovaries from prepuberta l gilts were collected at a local slaughterhouse. Oocytes were cultured in a hypoxanthine (HX 4 mM) containing M 199 for 24 or 40 h with or without fo rskolin and FSH treatment. After the culture, we examined germinal vesicle breakdown (GVBD) and polar body (PB) formation. Two experiments were design ed. (1) Cumulus enclosed oocytes (CEO) were cultured for 24 or 40 h with or without different doses of forskolin and FSH. (2) CEO were primed by forsk olin and FSH for different times and then transferred into an HX-medium for a further culture. The total culture period was 24 h. The results revealed that 4 mM HX markedly prevented pig CEO from undergoing GVBD. After 24 and 40 h culture, FSH (50-200 U/L) stimulated oocytes to resume meiosis by ove rcoming the inhibition of HX. Both GVBD and PB formation were increased (P < 0.002 and 0.01 respectively) after 40 h exposed to FSH. Forskolin showed a biphasic effect on CEO maturation. Within 24 h forskolin, in combination with HX, inhibited oocytes maturation. The GVBD percentage was significantl y decreased compared to HX alone group (2% to 20%, P < 0.01), whereas no in hibition was observed after 40 h of culture. The second experiment showed t hat forskolin (3 mu M) and FSH (100 U/L) priming CEO could time-dependently induce oocyte maturation by overriding the inhibition of HX. After 30 and 60 min priming by FSH or forskolin, the GVBD and PB percentage was signific antly increased (P < 0.002 and 0.01 respectively). No difference of GVBD pe rcentage was observed between FSH short time priming group and FSH long tim e presentation group. In conclusion, we found that forskolin and FSH in vit ro can stimulate pig cumulus cells to secrete a meiosis-activating substanc e which induces the oocyte to overcome the inhibition of hypoxanthine and u ndergo GVBD. (C) 2000 by Elsevier Science Inc.