Regulation of testicular LH receptors by homologous hormone: in vitro studies on receptor occupancy and receptor loss.

A method is described which makes use of 4M MgCl₂ to dissociate the testicular luteinizing hormone-receptor complex without altering either the binding capacity or binding affinity of the receptor. Using this method, it was demonstrated that $\text{in vitro}$ incubation at 4° of decapsulated rat testes with various concentrations of luteinizing hormone or with human chorionic gonadotropin resulted in a reduction in binding capacity. This reduction of binding capacity could not be completely accounted for by occupation of receptors by homologous hormone, suggesting that receptors were lost. Thus negative regulation of LH receptors by LH and hCG was observed. The reduction in LH binding capacity was specific for LH and hCG, dose dependent and time related. FSH, prolactin and growth hormone did not exert the same effect.