Similar to follicles, the bovine corpus luteum also displayed stage-specific changes in the follistatin levels. When the corpus luteum was developing but not yet fully functional, immature luteal cells did not display any immuno-staining for follistatin; the amount of staining increased with maturity of the corpus luteum (maximum at mid-dies-trus) and decreased again during regression. Our results are consistent with earlier reports in which expression of fol-listatin mRNA or protein was detected in the corpus luteum of the cow, ewe, and human. In the rat, the primary gonadotropin surge appeared to suppress the expression of follistatin and follistatin mRNA, and the protein declined sometime prior to, or immediately after, ovulation. Similar changes may also occur in bovine granulosa cells in which follistatin expression ceases during the late preovulatory stage. We found that not all luteal cells displayed follistatin immunostaining, and the cells that were positively stained were in close proximity to blood capillaries. In the present study, no attempt was made to distinguish between the large and small luteal cells, but results provide rationale for the hypothesis that luteal cells that are derived from the granulosa layer synthesize follistatin. It is not yet clear what specific role is played by the follistatin in the luteal cells. buy yasmin online
In summary, follistatin was detected in the granulosa layer of healthy bovine follicles and in luteal cells of dies-trous corpora lutea. The degree of immunohistochemical expression of follistatin was phase specific for both follicles and corpora lutea. The most intense staining was associated with the period of functional dominance (growing, early-static, and preovulatory phases) in dominant follicles and during the phase of maximal luteal gland development in diestrus. Results suggest that follistatin may be involved in the control of the final stages of follicle and luteal gland development in cattle, and that production or secretion involves an endocrine route.