Studies on the prolactin-releasing capacity of luteinizing hormone releasing hormone in male subjects.

The present study examined the conditions under which LHRH is capable of releasing PRL in the human male. No such effect was found in eugonadal males. After pretreatment with 100 micrograms ethinyloestradiol/day, but not with 30 micrograms/day, the PRL-releasing action of LHRH became apparent. This indicates that high doses of oestrogens are required. This effect of LHRH on PRL release was still demonstrable two weeks after withdrawal of oestrogens. This suggests that rather than oestrogens per se, alterations in the control of PRL induced by oestrogens, render the lactotroph sensitive to LHRH. Further: No effect was observed after administration of a bolus LHRH, whereas LHRH administered as an infusion released PRL with a latency period of 20-40 minutes. The interpretation for this could be that LHRH acts indirectly via a LHRH-induced decreased dopaminergic tone, which mechanism requires a certain amount of time. It is hypothesised that a LHRH-induced decrease of dopaminergic tone together with a weakened dopaminergic control of the oestrogenised lactotroph could account for this non-specific action of LHRH on PRL release.