Ruolo degli oppioidi endogeni nella maturazione in vitro dell’ovocita bovino

Summary In this study, the effects of endogenous opioids on the meiotic matu- ration of bovine oocytes were evaluated. The opioids antagonist Na- loxone (Nx) inhibited maturation, by blocking oocytes at the metapha- se I (MI) stage, or inducing chromosomal abnormalities, when added to the culture medium at the concentration of 1x 10 ^ - 3 M whereas its ad- dition at 1 * 10 ^ - 8 M enhanced maturation. The presence of the u-opioid receptor transcript in cumulus-oocyte complexes was demonstrated by means of RT-PCR. Oocyte preincubation with the calcium chelator BAPTA-AM counteracted the inhibitory effect of Nx. Increase in intra- cellular calcium was observed in cumulus oophorus cells after Nx treatment, thus demonstrating that the calcium is the signal responsible for the inhibition of oocytes maturation at high Nx concentration. B-en- dorphin inhibited oocytes to reach full maturation at the MII stage and increased the rate of oocytes arrested MI. These data, taken together, indicate a regulatory, inhibitory role of endogenous opioids on meiotic maturation of cow, exerted at the MI - MII transition.