Relationships between aromatase activity, follicular fluid oestradiol-17β and testosterone concentrations, and diameter and atresia of individual ovine follicles

摘要

Summary. Aromatase activity was measured in granulosa cells using a 1-h in-vitro assay. This activity correlated with the concentration of oestradiol-17β and the ratio of oestradiol-17β to testosterone in follicular fluid of individual follicles ranging from 1·5 to 7·0 mm diameter. These data show an 8–10-fold difference in aromatase activity between small and large follicles and that aromatase activity per cell increased in small non-atretic follicles (<3·5 mm) whereas it remained relatively constant in large nonatretic follicles (≥3·5 mm). Aromatase activity was much lower in follicles at more advanced stages of atresia. Atresia was assessed using the morphological and the morphometric methods (% of maximum number of granulosa cells/follicle). Although the morphological method of assessment was preferable to the morphometric method, it did not differentiate a decrease in aromatase activity as a very early event in the atretic process. We believe this is due to the inability of these methods to detect follicles in the initial stages of atresia.