FUNCTIONAL-ANALYSIS OF ACTIVATION OF PORCINE OOCYTES BY SPERMATOZOA, CALCIUM IONOPHORE, AND ELECTRICAL PULSE

The present study was conducted to examine differences in the activati on of pig oocytes induced by sperm penetration or the artificial stimu lators calcium ionophore A23187 and electrical pulse. Cumulus-oocyte c omplexes were cultured in NCSU 23 medium supplemented with 10% pig fol licular fluid and 0.57 mM cysteine for 44 hr and then freed from cumul us and corona cells prior to activation with A23187 or an electrical p ulse or inseminated with frozen-thawed ejaculated semen. Cortical gran ule (CG) exocytosis, zona reaction, nuclear activation, and developmen tal ability were examined after treatment. A23187 and electrical pulse induced 75.7% and 76.9% of CGs to be released from oocytes. Sperm pen etration induced 86.3% of CGs to be released from the oocytes, which w as significantly higher (P < 0.05) than those induced by artificial st imulators. Activation induced by A23187 and sperm penetration resulted in a zona reaction, which prevented sperm penetration after inseminat ion or reinsemination, respectively. Activation induced by electrical pulse, however, did not cause a zona block since the penetration rate (80%) of oocytes was not different (P > 0.05) from that in control ooc ytes (87%). Electrical pulse induced 87% of the oocytes to form a pron ucleus(ei), with 53% failing to release the second polar body. A23187 induced 62% of oocytes to form a pronucleus(ei), and 81% of these oocy tes released the second polar body. Sperm penetration induced 98-100% of the oocytes to release the second polar body and form a female pron ucleus, and 88-89% of sperm penetrated oocytes formed a male pronucleu s(ei). Blastocyst formation of oocytes exposed to spermatozoa, electri cal pulse, and A23187 was 27%, 10%, and 4% at Day 6 and 28%, 11%, and 5% at Day 7, respectively (P < 0.05). More nuclei were observed in the blastocysts derived from in vitro fertilization (32.3 +/- 12.9) than artificial stimulators. These results indicate that different and poss ibly overlapping mechanisms may be involved in the activation of pig o ocytes by spermatozoa, electrical pulse, and A23187. (C) 1998 Wiley-Li ss, Inc.