EXPRESSION OF ANDROGEN RECEPTORS AND STEROIDOGENIC ENZYMES IN RELATION TO FOLLICULAR-GROWTH AND ATRESIA FOLLOWING OVULATION IN PIGS

Among the new antral follicles that develop after ovulation in pigs, t he incidence of atresia, based on granulosa cell apoptosis, increases between Days 5 and 7 of the estrous cycle. The purpose of this study w as to determine how follicular growth and atresia affected the express ion of some key enzymes regulating follicular steroidogenesis and andr ogen receptor on Days 3, 5, and 7 after the onset of estrus. Ovaries w ere frozen in liquid propane for subsequent sectioning and immunohisto chemical analysis. Ninety-six follicles were classified according to s ize as small (< 3 mm), medium (3-5 mm), or large (> 5 mm). Follicles i n the active stages of the cell cycle were identified by the presence of the cell proliferation-associated nuclear antigen Ki-67 in granulos a cells, Follicles with apoptotic cells were identified by in situ 3'- end labeling of DNA. Staining intensity of antigens on sections was as signed a numeric value (0-3). Follicles assigned a value > 1 for 3'-en d labeling in their granulosa cells were classified atretic. The perce ntage of atretic follicles increased (p less than or equal to 0.05) fr om 5% on Days 3 and 5 to 41% on Day 7. Expression of Ki-67 in granulos a cells was more strongly (p less than or equal to 0.05) associated wi th nonatretic follicles (98% expressing) than with atretic follicles ( 41% expressing). Aromatase cytochrome P450 (P450(arom)) was localized predominantly in granulosa cells of nonatretic follicles and was undet ectable in atretic follicles. Androgen receptor in granulosa cells and expression of P450 17 alpha-hydroxylase/C-17-20 lyase (P450(c17)) in theca interna were lower (p less than or equal to 0.001) in atretic fo llicles than in nonatretic follicles. The expression of 3 beta-hydroxy steroid dehydrogenase (3 beta HSD) was localized to the theca interna and was unaffected by follicle atresia. In nonatretic small follicles, the expression of P450(arom), and P450(c17), decreased (p < 0.01) bet ween Days 3 and 7 while expression of Ki-67 was unchanged. In nonatret ic follicles, increased follicle size was associated with a decrease ( p < 0.01) in androgen receptor expression and increases (p < 0.01) in P450(arom), P450(c17), and 3 beta HSD expression. In conclusion, incre ased expression of steroidogenic enzymes was associated with follicula r growth. Loss of P450(arom), expression in vivo is an early event in atresia and is followed by decreased cell proliferation, and decreased expression of androgen receptor and P450(c17).