Submitted to: International Congress on Animal Reproduction
Publication Type: Abstract Only
Publication Acceptance Date: May 8, 2000
Publication Date: N/A
Technical Abstract: Inhibins and activins (I/A) have the capacity to inhibit and stimulate, respectively, FSH secretion and synthesis in anterior pituitaries. The predominant I/A form produced in the pituitary is activin as beta A and B mRNA are present, while alpha mRNA is non-detectable. Immunoblots of nonreduced and reduced follicular fluid indicate that the four predominant forms 121, 69, 227, and >227 kDa (representing 83% of total inhibin immunoblot activity) are probably composed of dimers of inhibin A or B. The expression of alpha and beta A mRNA in granulosa cells is positively correlated with expression of aromatase protein, follicle growth and with expression of a cell proliferation marker, the cell proliferation- associated nuclear antigen Ki-67. In addition, expression of both à and A mRNA were also positively correlated with follicular diameter and with follicular estradiol during the period of selection and growth in the presumptive ovulatory follicles. In large follicles following the preovulatory LH surge expression of cc mRNA decreased by 72% while beat A and B mRNA decreased to low to non-detectable levels. Activin has been shown to inhibit granulosa cell steroidogenesis in vitro, suggesting an atretogenic role. However, during atresia expression of alpha and beta A mRNA were reduced by 66-83% compared to nonatretic follicles. Total inhibin immunoblot activity was 59% less in atretic than in nonatretic follicles and amounts of the 44-, 49-, 69-, 121- and 227-kDa forms were 50 to 80% lower. In summary, in addition to regulation of FSH secretion, the expression of alpha and beta mRNA in granulosa cells is related to the physiology of follicle growth in a positive way that appears to be independent of changes in FSH secretion.