Early hCG-induced desensitization in Leydig cells.

The early mechanism of hCG induced down regulation of its own receptor as well as steroidogenesis refractoriness of rat Leydig cells to gonadotropin stimulation have been investigated. A single injection of 5, 12, 25, 50 and 100 IU of hCG in rats induced within 8 hours, Leydig cells desensitization. However, apparent receptor loss was significantly lower only in the rats who received 50 and 100 IU of hCG. Cycloheximide inhibits hCG-induced receptors loss but had no effect on hCG-induced desensitization. The most likely explanation for desensitization in the presence of binding sites and a normal adenylate cyclase, is a defective coupling between the receptor sites and the catalytic subunit.