HCG-induced changes in the number of rat testis LH/HCG receptors

Adult male rats were injected subcutaneously with a mixture of hCG and [125I]hCG (3, 5, 10, 100 or 1000 IU), and killed 3, 6, 16, 24 or 48 h after injection. Specific uptake of [125I]hCG by the testes as well as the remaining in vitro binding capacity were measured. Cycloheximide (1.5 mg/kg) was given together with hCG to another group of animals. The effect of hCG on testicular LH/hCG receptors was found to consist of two phases: first, 6--16 h after injection, a significant increase in the binding capacity occurred, which was found with the lower 3--10 IU doses of hCG. Thereafter there was a pronounced decrease in receptor concentration, which was directly correlated to the dose of hCG. Experiments with cycloheximide suggest that the decrease in binding, but not the increase, is at least partly dependent on protein synthesis.