The effect of endogenous and exogenous gonadotrophin-releasing hormone on the prolactin response to TRH.

The prolactin response to TRH in a group of patients with Kallmann's syndrome was found to be significantly lower compared to a group of hypergonadotrophic hypogonadal patients. Since levels of testicular products are comparably low in both groups, we hypothesize that high endogenous LHRH production might be associated with an increased prolactin response to TRH. In support of this, we were, indeed, able to establish a positive correlation between the magnitude of the prolactin response to TRH and basal and LHRH-stimulated LH/FSH levels (the latter serving as an index of endogenous LHRH production) in: (1) eugonadal men, (2) men with Kallmann's syndrome, (3) oestrogen-treated agonadal men, (4) men with severely impaired spermatogenesis and, (5) agonadal men. A direct relation between LHRH and the prolactin response to TRH was demonstrated in a group of eugonadal men, the prolactin response to TRH being greater after prolonged LHRH pretreatment. We speculate that an increase of endogenous or exogenous LHRH might be associated with decreased hypothalamic dopamine secretion which could directly increase prolactin synthesis. Indirectly, decreased dopamine secretion could augment the potency of TRH in releasing prolactin.