EFFECT OF TESTOSTERONE AND DIBUTYRYL-CAMP ON THE MEIOTIC COMPETENCE IN PIG OOCYTES OF VARIOUS SIZE CATEGORIES

Spontaneous meiosis resumption was investigated in small pig oocytes o f various size categories. Two parameters were studied: 1) the possibi lity for inhibiting spontaneous meiosis resumption in small oocytes of various size categories and 2) the level of meiotic competence of sma ll oocytes in which meiosis resumption had been temporarily blocked. I t was observed that 1 mM dibutyryl cyclic adenosine monophosphate (dbc AMP) combined with 0.5 mu M testosterone were able to prevent spontane ous maturation in pig oocytes of various size categories cultured in v itro for up to 10 d. Moreover, a culture of these oocytes with dbcAMP and testosterone has a beneficial effect on the integrity of the oocyt e-granulosa cell complex. When oocytes were allowed to mature after lo ng-term inhibition of maturation, the percentage of oocytes able to re sume maturation was significantly increased. However, the portion of o ocytes which completed maturation, reaching the metaphase II (M II) st age, did not increase. It was found that dbcAMP, in combination with t estosterone, also efficiently inhibited spontaneous maturation in full y grown pig oocytes. When the inhibitory effect of dbcAMP and testoste rone was reversed in fully grown oocytes, maturation was significantly accelerated.