The present study was performed to evaluate the expression and function of P-glycoprotein (P-gp) encoded the multidrug resistance type I (MDR1) gene, protecting from xenotoxics, in porcine oocyte during in vitro maturation. Cumulus-oocyte complexes (COCs) were cultured to obtain the germinal vesicle (GV), first metaphase and second metaphase (MII) oocytes. The P-gp function was assessed by means of the rhodamine 6G (R6G) efflux from oocytes with P-gp inhibitors such as verapamil and PSC-833. The MDR1 transcript was detected in the GV and MII oocytes by RT-PCR analysis using primer sets based on the human gene. P-gp inhibitors significantly blocked the R6G efflux from the MII oocytes, whereas the reagents were ineffective in the GV oocytes. The R6G efflux from oocytes was accelerated at the MII stage more than at the GV stage. Thus, the MDR1-type P-gp function is poor at the GV stage, but the function improves during oocyte maturation.
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