Comparisons of steroid production and density of LH binding sites in guinea pig ovarian follicles destined to ovulate and destined to become atretic

Abstract

Two waves of follicular recruitment exist in the 16-day estrous cycle of the guinea pig. One lasts from days 2 to 10 and contains follicles that are all destined to become atretic, while another lasts from days 7 to 16 and includes several follicles destined to ovulate. Healthy-appearing follicles of greater than 0.6 mm were isolated on days 6, 9, and 15 of the cycle to investigate specific characteristics of the two consecutive waves of follicles. Follicles were compared on the bases of LH binding site density and steroid synthetic capacity. Large day-9 and day-15 follicles were shown to have similar densities of LH binding sites and also were capable of synthesizing and secreting large amounts of estrogen following incubation in media supplemented with hCG or testosterone. However, only day-15 large follicles were able to produce large amounts of estrogen in unsupplemented media, which suggests that they had already been exposed to endogenous LH prior to their removal from the ovary. Estrogen production by the large day-9 follicles was negligible when they were incubated in unsupplemented media. These follicles of the first wave of folliculogenesis would not have experienced a similar exposure to endogenous LH in vivo, since it is known that serum concentrations of LH are low during days 6–10 of the cycle. It is postulated that the lower estrogen production by large day-9 follicles may also be associated with the inability to undergo other maturational events essential for ovulation.