Artificial activation of porcine oocytes matured in vitro.

These studies were undertaken to understand the biological basis of artificially induced activation of meiotic metaphase II oocytes and to develop a source of oocytes as recipients for cloning by nuclear transfer. In vitro matured porcine oocytes were pulsed with various voltages of electricity and evaluated for pronuclear formation. The percentage of eggs that activated was significantly greater for the higher voltages. The effect on activation of the temperature of the ovaries returning from the abattoir was evaluated and it was found that oocytes derived from ovaries returning at 29 degrees C activated at lower rates (45.5%) than those returning at 36 degrees C (78.9%). An experiment was designed to evaluate the pH of electroporation medium (EM) and the duration of exposure to EM on activation. Oocytes were placed in EM at various pHs for 5 minutes, pulsed, and immediately removed to TL-Hepes or allowed an additional 2 minutes in EM prior to rinsing in TL-Hepes. The results indicate an optimum activation rate at a pH of 7.0 and allowing the additional 2 minutes in EM. Additional glucosamine (5 mM) had no affect on development of the oocyte to metaphase but reduced the percent pronuclear formation from 61% and 47%. A final experiment evaluated the developmental competence of oocytes subjected to a optimum combination of the above treatments and illustrated that a significant portion of the activated oocytes can show limited signs of cleavage. Thus in vitro matured pig oocytes can be induced to activate at high rates.