Prolactin-releasing action of LRF: a central catecholamine mediated event?

Decline of plasma dopamine (DA), norepinephrine (NE), and epinephrine (EP) levels after iv administration of a 100 microgram bolus of LRF has been reported in normal men. This finding has been used to support the concept of a central dopamine mediated mechanism for LRF-induced PRL release. In the present study (including 5 postmenopausal women and 4 normal men), no detectable changes were found in plasma levels of DA, NE, EP and the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) following LRF (100 microgram iv) administration. These results pertain to both groups of subjects, although the PRL increment was 2-fold greater in the postmenopausal women than in the normal men. It is concluded that peripheral administration of LRF causes no acute decline of plasma catecholamines, and that the LRF-induced release of PRL may be based on the recent demonstration in vitro of a paracrine effect, gonadotrope to lactotrope.