Increase of follicle cell LH binding and changes in the LH level of follicular fluid during the preovulatory period in the sow

This study used the technique of histoautoradiography to analyze the varia- tion of LH binding in sow follicles during the preovulatory period.Estrus was synchronized by methallibure to obtain a reference point for dating the onset of the follicular phase of each sow in the experiment.In follicles increasing in diameter from 2.6 mm at days 0 and 1 of the follicular phase to 6.6 mm at day 6, granulosa 125 1_oLH or 125 1-pLH binding increased by 14 times while that of the theca interna increased by 2. The binding of these hormones remained high during and after the end of the ovulatory LH surge, at least until several hours before ovulation.Variations in plasmic as well as intrafollicular LH levels were radioimmunologically assayed.High intrafollicular levels of estradiol-1 7p at day 3 would explain the large increase of granulosa LH binding between days 4 and 5-6, in turn causing the intrafollicular level of progesterone to rise at day 5.These results indicated an interde- pendence between hormonal levels and target cell receptivity.Introduction.Gonadotropins induce the growth and maturation of follicles and oocytes by binding to the membrane receptors.Thus, during follicular growth in rats, receptors appear in the granulosa : FSH receptors are seen first, and then, under the action of that gonadotropin, LH receptors appear (Zeleznick et al., 1974 ; Richards et al., 1976 ; Nimrod et al., 1977).Concomitantly, the follicular fluid is first rich in FSH then in LH (women : McNatty et al., 1975).Gonadotropic action in the granulosa is thus sequential, while the theca interna always appears to bind LH.Since these data cannot be generalized from a small number of species, this report studies LH receptor variation and the intrafollicular penetration of this hormone in sows.Most of the work on follicular receptors uses tissue homogenate preparation.For instance, Kammerman and Ross (1975), Stouffer et al. (1976).-and Lee (1976)