The Relationship Between Plasma Testosterone and Mean LH Levels in Men

Abstract

We have studied the relationship between plasma testosterone and LH levels in normal men and in men with azoospermia due to primary testicular disorders. The degree of variability of the plasma testosterone was first quantitated and a good correlation (r = .908) was found between a single plasma testosterone and the mean over the 3-h period. The testosterone and mean LH levels were then found to be correlated in azoospermic men, though not in normal men. The correlation was virtually identical whether calculated from the testosterone concentration (r = 0.653) or from its logarithm (r = 0.631). The curvilinear plot of log testosterone vs. LH best fitted the data found in profoundly hypoandrogenic men. This curve seems to describe the testosterone-LH dose-response relationship. The variance of the data was not reduced by analysis of plasma free testosterone or of total androgen levels. There was a correlation between LH and FSH, but none between LH and serum estrogen levels. The slope of the curve relating testosterone and LH was found to be quite shallow in the normal and moderately low range of plasma testosterone. Furthermore, the LH levels of the azoospermic men were higher than those of normal men at comparableandrogen levels. Leydig cell reserve was found to be normal in the subset of the infertile group who did not have Klinefelter syndrome. On the basis of these observations, we hypothesize that the neurosecretory control mechanism for LH secretion is not “set” simply to maintain a normal plasma testosterone level, but is also closely linked to the factors regulating spermatogenesis.