Control of follicular deviation in the mare

The eminent selection event during a follicular wave is characterized by continued growth of the developing dominant follicle and reduced growth of the remaining (subordinate) follicles, known as deviation. The deviation mechanism is controlled by the interaction between gonadotropins and intrafollicular factors. The main goal of this series of experiments was to characterize the role and relationships of plasma gonadotropins and intrafollicular factors, IGF1 in particular, at follicular deviation in the mare. The first objective was to determine the effect of suppression of FSH with a GnRH antagonist (Acyline) before and during follicle deviation in the mare. The second objective was to study the functional relationships among intrafollicular insulin-like growth factor 1 and circulatory gonadotropins. The third objective was to study the differential roles of FSH and LH on the initiation of follicular deviation. Results indicated that Acyline was an effective suppressor of FSH before and during follicle deviation. During the low gonadotropin concentrations from Acyline treatment at deviation, intrafollicular IGF1 stimulated follicular growth and inhibin concentrations, but not intrafollicular estradiol production. During the first 48 h after the beginning of deviation, FSH alone maintained follicular growth and intrafollicular concentrations of free IGF1 and estradiol without an additional effect of LH.