The Effect of Short-Term Testosterone Administration on Serum FSH, LH and Testosterone Levels: Evidence for Selective Abnormality in LH Control in Patients with Klinefelter's Syndrome

Abstract

The pituitary-gonadal feedback control mechanisms were evaluated in patients with Klinefelter's syndrome (KS) by measuring the gonadotropin response to the administration of testosterone. A similar evaluation was performed on normal men for comparison. Six patients with KS and 4 normal men received 100 mg testosterone propionate intramuscularly (im) daily for 4 days. Serum luteinizing hormone (LH) and serum follicle-stimulating hormone (FSH) titers were measured before, then daily during testosterone administration, and for 4 consecutive days following the last dose. Serum LH levels in the patients with KS initially fell but then increased to baseline values or above. The rise in serum LH levels occurred while testosterone was still being administered and serum testosterone levels were markedly elevated. In contrast, serum LH levels remained depressed in the normal males following testosterone administration. FSH levels showed comparable suppression in the 2 groups. The biphasic serum LH response following testosterone administration indicates that patients with KS may possess a selective abnormality in their testosterone-LH feedback mechanism. Furthermore, the dichotomy between LH and FSH patterns observed in patients with KS following testosterone administration suggests that these gonadotropins have separate feedback control mechanisms.