Uptake of Luteinizing Hormone by the Preovulatory Monkey Follicle in Vivo*

The concentration of LH in the follicular fluid of the rhesus monkey during the late follicular phase of the menstrual cycle was measured using a radioreceptor assay (RRA) and a heterologous ovine: antiovine RIA. During the late follicular phase of the cycle there was no significant correlation between the concentration of LH in the follicular fluid and the size of the follicle. The concentration of radioimmunoassayable LH present in follicular fluid during the ascending portion of the LH surge was directly proportional to the concentration of LH in the serum. In contrast, using RRA, the concentration of LH in follicular fluid was relatively constant in spite of a rise in serum LH. These results suggested that radioreceptor-assayable LH may bind to receptors of the follicle during the rise in serum LH during the ascending portion of the midcycle gonadotropin surge. Additional evidence for uptake of LH into the ovary was obtained by examining the difference in LH concentration in peripheral venous blood (P) and ovarian venous blood (V) as a function of the concentration of LH in the P. The magnitude of the P-V difference increased with increasing peripheral venous serum LH concentrations. Removal of the preovulatory follicle resulted in a significant decrease in the P-V difference. These results were similar when either the RIA or RRA was used to measure the LH. During the late follicular phase of the menstrual cycle there was an increase in the concentration of progesterone in the serum, follicular fluid, and ovarian vein associated with an increase in LH. These findings were consistent with the concept that LH binds to cells of the preovulatory follicle during the ascending portion of the midcycle LH surge and that this binding results in the initiation of steps which are required for the production of follicular progesterone.