REGULATION OF PRIMATE TESTICULAR LUTEINIZING-HORMONE RECEPTORS AND STEROIDOGENESIS

The testicular luteinizing hormone (LH) receptors of the rhesus monkey and human have many features in common, including high equilibrium association constant, marked species specificity and relatively low binding capacity. Rhesus monkeys were used as models for human LH-receptor regulation in vivo during gonadotropin treatment. In 4 adult male monkeys treated with 10,000 IU human chorionic gonadotropin (hCG), serum and testicular steroidogenic responses were monitored at 24 h intervals during the following 4 days and LH-receptor concentrations were measured by 125I-hCG binding to 15,000 g particles prepared from testis biopsy specimens. In treated animals, serum hCG was maximal on day 1 at 322 .+-. 16 ng/ml and declined to 24.4 .+-. 2.3 ng/ml by day 4. Serum testosterone was increased 3-fold during the subsequent 4 days (from 6.5 .+-. 2.0 to 18.6 .+-. 4.4 ng/ml) but serum progesterone remained unchanged. Serum 17.alpha.-hydroxyprogesterone increased 12-fold to 5.5 .+-. 0.5 ng/ml at day 1 and was increased 4-fold during the subsequent 3 days. The LH-receptor binding capacity of the primate testis was reduced by 18.3 .+-. 6.0% on day 1, 51.7 .+-. 7.4% on day 2, and 45.3 .+-. 2.4% on day 4. Occupancy of the LH receptors by endogenously bound hCG was significant on day 1 but was negligible by day 4. Gonadotropin-induced LH-receptor depletion occurs in the rhesus testis and primate gonadotropin receptors are susceptible to the regulatory processes recently described in the rat. In addition, the simultaneous and disproportionate accumulation of 17.alpha.-hydroxyprogesterone indicates that 17,20-desmolase was rate-limiting under these conditions in the primate testis Leydig cell.