Changes in luteinizing hormone receptors in the granulosa and theca layers of the ovarian follicle during follicular maturation in the Japanese quail

Abstract

Attempts were made to reveal changes in number and affinity of LH receptors in the avian ovary during the course of the final maturation of follicles. First, we characterized the hormone binding properties of LH receptors in ovarian follicles of the Japanese quail by incubating a crude plasma membrane preparation of follicle layer with radioiodinated chicken LH prepared by a recently devised method. Specific LH receptors with common binding properties were detected in both granulosa and theca layers of large preovulatory follicles. The binding affinity of the receptors in the quail ovary to chicken LH ( K a: 2.9 ∼ 17.2 × 10 9 M −1) was similar to that of gonadal LH receptors of other vertebrates. Optimal temperature and pH for the binding of chicken LH to the receptors of quail were also similar to those reported for LH receptors of mammals. Secondly, we compared the bindings of chicken LH to the receptors in the follicular layers of the largest three follicles. Specific binding to the crude plasma membrane preparation of the theca layer differed slightly between the third and second largest follicles, but decreased abruptly to about one-third in the largest follicle that was expected to ovulate within 24 hr. This change was explained mainly by a decrease in the number of receptors. The specific binding of chicken LH to receptors in the granulosa layer did not differ significantly among the largest three follicles. The decrease in the number of LH receptors in the theca layer may cause the following sequential events in the largest follicle: decrease in the sensitivity of theca cells to LH, decrease in the estradiol-17β production, reduction of inhibition of progesterone production in granulosa cells, active secretion of progesterone, and ovulation.