Klinefelter’s syndrome: effects of short-term testosterone administration on hypothalamic-pituitary axis function

Abstract

The response of pituitary gonadotropins to GnRH was tested in a group of patients with Klinefelter’s syndrome (KS) and in normal controls. Plasma LH, FSH, PRL, testosterone (T), 5 α-dihydrotestosterone (DHT) and 17 β-estradiol (E2) were also measured in the same subjects during and after testosterone propionate (TP) administration (100 mg im daily for 4 days). Both plasma FSH and LH response to GnRH was increased in KS. However LH increment was significantly different from that of normal controls only 90 min after the GnRH injection; FSH increment reached levels from five to tenfold greater than that of normal controls just 20 min after the start of the test. During the TP suppression test plasma T and E2 levels in KS showed a pattern similar to normal controls, while the increase of plasma DHT reached approximately 50% of normal controls. FSH suppression was similar to normal subjects, while LH suppression was less consistent and shorter. These data seem to confirm that in KS the hormonal mechanisms controlling FSH release are more sensitive to stimulation and inhibition than those controlling LH release. Moreover, in KS, plasma PRL levels showed a significant increase (p< 0.05) 24 h after the first TP injection and remained elevated till the last day of the test. PRL increase does not seem related to circulating E2 levels because no significant differences were observed between E2 plasma levels in the two groups during TP administration. The PRL hyperresponsiveness in KS could be related to the inbalance between androgens and estrogens of these patients.