Glycoconjugates changes induced by β-endorphin in equine oocytes

Glycoconjugates play a key role in oocyte maturation and in oocyte-sperm interactions leading to fertilization. We previously showed that -endorphin inhibits oocyte maturation. We here investigated the effects of-endorphin on the expression of glycoconjugates in equine oocytes by lectin histochemistry. Cumulus enclosed oocytes from abbattoir ovaries were fixed in Bouin’s solution and embedded in paraffin wax after in vitro maturation. Sections (5 m thick) were stained with 12 lectins (SNA, PNA, DBA, RCA120, SBA, HPA, Con A, WGA, GSA I-B4, GSA II, UEA I, LTA). The ooplasm of treated oocytes showed a reduced HPA staining and increased reactivity for Con A and GSA II, whereas SNA, RCA120, SBA, WGA, GSA I-B4, UEA I and LTA affinity did not change between groups, as well as PNA and DBA unstaining. The zona pellucida of treated oocytes displayed increased reactivity for SBA whereas SNA, RCA120, Con A and WGA were unaffected and binding sites were lacking for UEA I and LTA. Corona radiata cells from control oocytes reacted with all used lectins except for GSA II. β-endorphin incubation reduced the affinity for SNA and GSA I-B4 whereas it revealed GSA II reactivity and further binding sites for PNA, SBA and HPA. These results suggest that -endorphin modifies glycoprotein pattern in equine oocytes, mainly in corona cells. These modifications could be related to previously observed inhibitory effect of -endorphin on oocyte maturation and fertilizability.