EFFECTS OF THE GONADOTROPIN-RELEASING-HORMONE AGONIST, D-TRP-6-GNRH, ON PROLACTIN SECRETION IN HEALTHY-YOUNG MEN

The objective of this study was to examine the changes in basal plasma gonadotropin, cl-subunit, sex steroid, and prolactin levels and the p rolactin and luteinizing hormone (LH) secretion pattern before, during and 161 days after treatment with a depot preparation of D-Trp-6-GnRH in young men. Gonadotropins, alpha-subunit, sex steroids, and prolact in were measured in pooled plasma samples. Additionally, before treatm ent, several times during its course and on day 161 after treatment, b lood samples were drawn for 8 h every 15 min for prolactin and LH meas urements. After initial stimulation of the pituitary, administration o f a depot preparation of D-Trp-6-GnRH resulted in a constant decrease in gonadotropin and sex steroid concentrations with LH and testosteron e concentrations remaining within the limits of prepubertal levels fro m days 16 to 38. alpha-Subunit concentrations (0.4 +/- 0.09 IU/I; mean +/- SE) increased after application of D-Trp-6-GnRH, and remained ele vated until day 48. Basal prolactin levels (3.5 +/- 0.25 mu g/l) did n ot change significantly during treatment but afterwards increased cons istently with maximal levels at day 141 (15.3 +/- 3.8 mu g/l); they ha d decreased at day 161 to 10.3 +/- 1.8 mu g/l which is significantly h igher than before treatment (p < 0.05). On day 161, prolactin pulse am plitude was significantly higher than before and during treatment (p < 0.05), while no significant changes in pulse frequency occurred. No s ignificant temporal coupling between LH and prolactin release could be detected. In conclusion, after administration of a depot preparation of D-Trp6-GnRH to 6 young men, there was a rise in basal prolactin lev els and prolactin pulse amplitude as a long-term side effect of treatm ent, with maximal levels at 141 days after application.