Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 17, 1996
Publication Date: N/A
Interpretive Summary: The effect of gonadotropin treatment on proliferation of cells within ovarian follicles was examined in cows in which treatment was initiated on day 2 of the estrous cycle before a dominant follicle had emerged. This treatment protocol has previously been determined to produce a more consistent superovulatory response. Proliferation of follicular cells increased after gonadotropin treatment, proliferation was greatest in the antral most granulosa cells, and proliferation decreased as follicles increased in size. These findings will improve the design of subsequent studies because granulosa can be separated into subpopulations based on size, which reflects their difference in proliferative potential.
To determine the effects of gonadotropins (FSH-P) on size, number and cell proliferation of antral ovarian follicles, cows received FSH-P or vehicle beginning on Day 2 after estrus, and ovaries were collected 6, 12, 24, or 48 h after initiation of FSH-P treatment, or 24 or 48 h after initiation of vehicle treatment. Proliferating cells were immunolocalized in fixed follicles by using a specific primary antibody against proliferating cell nuclear antigen (PCNA), and the labeling index (LI; percentage of cells staining positively for PCNA) was determined for granulosa and thecal cells. After 48 h of treatment, FSH-P treated cows had fewer (P<0.01) small antral follicles and more medium and large antral follicles (P<0.01 and P<0.05, respectively) compared with vehicle-treated cows. Granulosa cell LI was negatively correlated (P<0.05) with follicular diameter for vehicle-treated but not for FSH-P treated cows. Analysis of covariance using follicular diameter as a covariate to adjust to a common diameter indicated that granulosa cell LI was greater (P<0.05) at 24 and 48 h in FSH-P treated than in vehicle-treated cows; conversely, thecal cell LI was greater (P<0.01) at 48 h in FSH-P treated when compared with vehicle-treated cows but was not different at 24 h. Across all groups, the LI of cells located within the antral half of the granulosa cell layer (P<0.01) than that of cells located within the basal half. In conclusion, stimulation of follicular development by exogenous gonadotropins increased or maintained proliferation of granulosa and thecal cells concomitant with continued follicular growth. Therefore, enhanced follicular cell proliferation may be an important mechanism by which gonadotropins superinduce growth of antral follicles in cows.