Development of multidrug resistance type I P-glycoprotein function during in vitro maturation of porcine oocyte

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.

The Roles of Vitamin A for Cytoplasmic Maturation of Bovine Oocytes

Vitamin A is one of the micronutrients which have been implicated in cattle reproduction. In cattle, ingested vitamin A, mainly as beta-carotene (BC) from forages and retinol ester from formula feed, is metabolized and transported to the oocytes and cumulus-granulosa cells in ovarian follicles through binding to various interacting molecules. The active form of vitamin A, retinoic acid (RA), functions as a regulator of gene expression in these targets. Early research showed the positive effects of vitamin A supplementation on bovine fertility in artificial insemination, and several studies on effects of vitamin A metabolites used in other artificial reproductive techniques (ART), including superovulation, ovum pick up, and in vitro maturation culture have provided evidence for the specific roles of vitamin A in oocyte cytoplasmic maturation (acquisition of developmental competence of oocytes during their meiotic maturation period for the embryonic development after fertilization). BC may enhance cytoplasmic maturation by its antioxidant properties which cannot be replaced by RA. Furthermore, RA may promote cytoplasmic maturation of bovine oocytes via its modulatory effects on the gene expression of gonadotrophin receptors, midkine, cyclooxygenase-2, and nitric oxide synthase in cumulus-granulosa cells.

Expression of Nitric Oxide Synthase-3 in Porcine Oocytes Obtained at Different Follicular Development

The present study was designed to determine the localization of nitric oxide synthase-3 (NOS-3) in porcine follicles during follicular development. A 130-kDa NOS-3 protein was found with greater frequency much in the oocytes than in the cumulus cells, as revealed by Western blotting analysis. The content of NOS-3 in the oocyte was higher in large follicles (> 7-mm diameter) than in small follicles (< 2-mm). The data by Western blotting showed the same pattern as the observations obtained from the immunohistochemical studies, in which the periphery of the oocyte stained strong positive. The inner surface cell layer of granulosa cells and cumulus cells were positive staining, especially in large antral follicles. In the primordial follicles, NOS-3 was restricted to the cytoplasm of oocytes, and no stained product was observed in the nucleus of oocytes or granulosa cells. A significant synthesis of NO by oocytes was observed in the presence of ionomycin, but not in the absence of ionomycin, indicating that oocyte NOS-3 functions in response to transient elevations in the intracellular calcium level. We concluded that NOS-3 is expressed in the oocyte from the primordial follicular stage to antral follicular stage, and that it is functional at least in the antral follicles.