Men with
hypogonadotropic hypogonadism (HH) due to hypothalamic-
pituitary disease present with low serum
testosterone levels combined with undetectable, low, or normal
gonadotropin levels. Treatment consists of
testosterone replacement to reverse the symptoms of
androgen deficiency. The aim of this study was to examine the dynamics and feedback inhibition of
follicle-stimulating hormone (FSH) and
luteinizing hormone (LH) in relation to
testosterone in 38 men with HH treated with
testosterone. Findings were compared with 11 men with primary hypergonadism (PH).
Testosterone replacement led to a suppression of FSH levels from 2.8 IU/L at baseline to 1.1 IU/L and to a suppression of LH levels from 2.3 to 0.8 IU/L. There was a linear correlation between levels of FSH and LH (after natural log transformation for both) and
testosterone levels in both the HH and PH groups. However, the differences in intercepts and slopes between the groups were significant. To determine whether nonsuppressed FSH or LH during
testosterone replacement reduces the probability of eugonadism, as reflected by normal
testosterone levels,
gonadotropin levels were measured and categorized as low (<0.5 IU/L), medium (0.5-2 IU/L), and high levels (>2 IU/L). The higher FSH or LH levels were found to significantly decrease the chance for achieving eugonadism. In conclusion, in men with HH due to hypothalamic-
pituitary disease or injury, the pituitary-testicular hormonal axis maintains its physiological negative feedback between
testosterone and
gonadotropins. Thus,
gonadotropin levels in men with HH might be useful, together with
testosterone concentrations, for assessing the adequacy of
androgen replacement.