Differential effects of single and repeated administrations of gonadotropins on luteinizing hormone receptors and testosterone synthesis in two populations of Leydig cells.

Luteinizing hormone (LH) receptor sites and in vitro testosterone production in response to human chorionic gonadotropin (hCG) stimulation (Leydig cell responsiveness) were studied in two distinct populations of Leydig cells after different modes of in vivo gonadotropin treatments.Dispersed cells from decapsulated rat testes were purified and separated into two distinct populations of Leydig cells, I and II, by centrifugation in a 0 to 40% Metrizamide gradient.The number of LH receptor sites per lo6 Leydig cells, as measured by '''I-hCG binding, was similar in the two populations.Leydig cell responsiveness was markedly greater in Leydig cell population I1 than I. Twice daily treatment with 6 or 12.5 p g of LH for 6 days produced a marked increase in responsiveness in population I, in spite of a 44 and 47% loss in receptor sites.The same treatment regimen produced only a slight increase in responsiveness in population 11, while LH receptor sites were reduced by 34 and 61% in these cells.A single subcutaneous administration of 150 pg of LH, a dose equivalent to the total dose of LH that was administered to rats on a twice daily regimen of 12.5 pg, had no effect on responsiveness in population I, but decreased in uitm testosterone production in response to hCG from 250 to 70 ng/106