Heterogeneity of prolactin and TSH response to TRH in hypotonadotropic hypogonadism

To evaluate prolactin and TSH secretion in isolated gonadotropin deficiency, thyrotropin-releasing hormone (TRH), in a dose of 500 microgram, was administered iv to fifteen male subjects with this disorder. In 4 out of 8 untreated patients, TRH-mediated prolactin release was significantly blunted and this attenuated response was not improved in one patient after treatment with testosterone for 1 year. In 7 patients who were treated with testosterone for 2 to 8 years, four failed to show a normal prolactin response after TRH injection. TRH-induced TSH secretion, on the other hand, was attenuated in two out of 8 untreated and in two of 8 treated patients with hypogonadotropic hypogonadism. The decreased TSH reserve was not necessarily associated with the poor prolactin response to TRH. It was concluded that heterogeneity exists in TRH-mediated prolactin and TSH release in "isolated" gonadotropin deficiency syndrome.