Effect of naloxone on gonadotropin secretion before and after testosterone in Klinefelter's syndrome

Role of the hypothalamic opioidergic system in the control of gonadotropin secretion in elderly men

The role of opioidergic system in controlling gonadotropin secretion in elderly men still remains uncertain. In the present study, we attempted to examine the opioidergic inhibitory tone imposed on GnRH release mechanism in elderly men by monitoring the plasma gonadotropin response to the opiate receptor antagonist naloxone hydrochloride. Six normal young men and 10 elderly men with no endocrinological diseases volunteered for the present study. In young men, plasma LH showed a biphasic increase in response to naloxone and plasma LH level during naloxone treatment was significantly higher than the mean of prenaloxone control levels. In contrast, plasma LH in elderly men was not affected by naloxone. The ratio of the peak plasma LH response during naloxone treatment to the mean pre treatment LH level (plasma peak/basal LH ratio) declined with the advance of age (r = -0.74, P < 0.005) and also correlated significantly with plasma free testosterone level (r = 0.45, P < 0.05). These data suggest (1) that the hypothalamic opioidergic tone is reduced in elderly men and (2) that the primary testicular insufficiency with the advance of age may play a major role in the decline of the hypothalamic opioidergic tone in elderly men.

Neuroendocrine regulation of pulsatile luteinizing hormone secretion in elderly men

Leydig cell function is driven by LH, secreted in a pulsatile manner by the anterior pituitary in response to episodic discharge of hypothalamic LHRH into the pituitary portal circulation, under control of a yet to be defined neural mechanism, the "hypothalamic LHRH pulse generator". The normal aging process in elderly men is accompanied by a decline in Leydig cell function. Whereas primary testicular factors undoubtedly play an important role in the decrease of circulating (free) testosterone levels with age, recent studies demonstrated that aging also affects the central compartment of the neuroendocrine cascade. Hypothalamic alterations comprise changes in the regulation of the frequency of the LHRH pulse generator with an inappropriately low frequency relative to the prevailing androgen impregnation and opioid tone, and with an increased sensitivity to retardation of the LHRH pulse generator by androgens. As observed by some authors in basal conditions and by others after endocrine manipulations. LH pulse amplitude seems also to be reduced in elderly men as compared to young subjects. This is most probably the consequence of a reduction in the amount of LHRH released by the hypothalamus. Indeed, challenge of the gonadotropes with low, close to physiological doses of LHRH in young and elderly men reveals no alterations in pituitary responsiveness when looking at either the response for immunoreactive LH or bioactive LH. Deconvolution analysis on data obtained after low-dose LHRH suggests a markedly prolonged plasma half-life of LH in elderly men, a finding which may explain the paradoxical increase of mean LH levels in face of the reduced or unchanged frequency and amplitude of LH pulses.