Effect of PMSG on follicular atresia in the immature rat ovary

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Abstract
PMSG [pregnant mare serum gonadotropin] administration to 26 day old rats did not increase the total number (non-atretic and atretic) of preantral (Type 4) and antral (Types 5 and 6) follicles but changed the proportion between non-atretic and atretic follicles. By 12 h after PMSG administration only 7% of Type 5 follicles were atretic, and no atretic follicles of Type 6 were observed, as compared to 42 and 62% atretic follicles, respectively, in the saline-treated controls. PMSG did not decrease the percentage of atresia in preantral (Type 4) follicles. The treatment was associated with a sharp fall by 12 h in the pyknotic index of antral (Types 5 and 6) follicles. PMSG apparently causes superovulation in the rat by rescuing follicles of Types 5 and 6 from atresia and allowing them to reach ovulation.