The effect of gonadotrophin releasing hormone on pituitary-gonadal function in Klinefelter's syndrome.

The mean basal plasma LH and FSH levels in 8 patients with Klinefelter's syndrome were respectively 5 and 15-fold higher than in 8 eugonadal males, whereas plasma testosterone concentration were half the normal value. After an intravenous bolus injection of gonadotrophin releasing hormone (100 mug of LH-RH) the gonadotrophin increase in the Klinefelter patients was more marked than in the control subjects, but in both groups the plasma testosterone levels remained essentially unchanged. In contrast to the bolus injection, an 8 h infusion of LH-RH after the bolus elicited a significant plasma testosterone increase in both the eugonadal males (59%) and the Klinefelter patients (51%). These findings indicate that despite an impressive endogenous hyper-gonadotrophism, Leydig cells in Klinefelter's syndrome can still respond to a sustained further increase of these endogenous gonadotrophins and thus still have functional reserve.