Responsiveness of gonadotropin secretion to infusion of an opiate-receptor antagonist in hypogonadotropic individuals.

We tested the hypothesis that suppressive effects of endogenous opiate substances are involved in certain hypogonadotropic states. For this purpose, we studied gonadotropin secretion in idiopathic hypopituitarism (five children), constitutionally delayed adolescence (five boys), and Kallmann's syndrome (three men). Endogenous opiate pathways were antagonized by the iv infusion of naloxone hydrochloride at a dose previously shown to elicit a prompt and significant increase in serum levels of LH in normal men. Under these conditions, naloxone did not increase serially sampled serum concentrations or mean urinary levels of LH: or FSH in eight patients with idiopathic hypopituitarism or Kallmann's syndrome. Gonadotropin concentrations in four of five patients with constitutional delay of adolescence also were unaffected. In one boy with clinical and biochemical indices of late pubertal development, naloxone elicited a significant increase in LH levels in blood and urine, similar to the pattern observed in normal men. In contrast to results in experimental animals, naloxone did not suppress serum PRL concentration significantly in any subject. These observations suggest that: 1) endogenous opiate mechanisms are unlikely to constitute a principal factor in maintaining hypogonadotropism in idiopathic hypopituitarism, delayed adolescence, or Kallmann's syndrome, at least acutely; 2) endogenous opiate mechanisms also cannot be implicated in the acute regulation or PRL secretion in children; and 3) the capability of adult men, but not early pubertal boys, to respond with increased gonadotropin secretion during inhibition of opiate receptors suggests that maturation of the opiate-related neuroendocrine system occurs during the course of sexual development in the human.