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 variation 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 _oLH or 125 -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 interdependence between hormonal levels and target cell receptivity.