Endocrine control of human spermatogenesis

Abstract

We performed a series of studies in normal men to determine the relative roles of FSH and LH in the regulation of human spermatogenesis. Experimental gonadotropin deficiency was induced in normal men by administration of high-dosage testosterone (T) enanthate, resulting in suppression of spermatogenesis to severely oligospermic or azoospermic levels. In these gonadotropin deficient normal men, we found that selective replacement of either LH activity, with human chorionic gonadotropin (hCG) or hLH, or FSH activity with hFSH increased sperm counts into the 20–50 million/ml range, but quantitatively normal spermatogenesis was not achieved. To determine whether both LH and FSH together are required for quantitatively normal spermatogenesis, selective FSH deficiency was induced in normal men by administration of hCG. In the setting of high LH-like activity and markedly suppressed FSH levels induced by hCG, sperm production was partially suppressed again into the 20–50 million/ml range. Replacement of FSH activity, with either hFSH or human menopausal gonadotropin in hCG-treated normal men stimulated sperm production into the control range in all subjects. These studies demonstrate that neither normal serum levels of FSH or LH are required for qualitatively normal spermatogenesis in man, since sperm counts in the range of 20–50 million/ml are found in states of selective FSH or LH deficiency. However, normal levels of both FSH and LH are required to achieve quantitatively normal sperm production in man.