Follicular size and steroid secretion of dominant bovine follicles

Twenty one estrogen-active bovine follicles obtained in the preovulatory period prior to the endogenous LH peak were superfused for 10h. Follicular diameter and superfusate estradiol (E2), testosterone (T) and progesterone (P4) were measured. A close correlation between follicle size and E2 secreted into the superfusate was found (r = 0.77; p less than 0.01). There was no correlation between superfusate T or P4 and follicular diameter. These data indicate that within certain limits the amount of E2 secreted can be predicted by follicle size in an in vitro superfusion system. As follicle size correlates closely with granulosa cell number in estrogen-active follicles, one can speculate that the rise in estrogen secretion is a reflection of an increase in granulosa cell number of the dominant bovine follicle. The application of these in vitro findings to the in vivo situation might help in the interpretation of the quality of ovarian stimulation with hMG/hCG.