125I-LH binding to rat testes at various ages and posthypophysectomy

Binding of 125I-LH by the rat testes was investigated during various stages of sexual maturation and in mature animals following hypophysectomy. Hormone binding per mg testicular tissue increased with age and was shown to be due to larger receptor concentration rather than greater binding affinity. This observation cannot be accounted for by changes in the relative number of Leydig cells and suggests, therefore, that Leydig cells acquire additional receptors during sexual maturation. Binding of 125I-LH to mature testes declined after hypophysectomy. Three days following pituitary removal the LH-receptor concentration decreased to one half of normal control value, then remained unchanged until the 37th post-operation day. Replacement therapy with LH, FSH or testosterone propionate failed to maintain 125I-LH binding at prehypophysectomy level.