Effects of Drugs Infused into a Rat Hypophysial Portal Vessel on Prolactin and Growth Hormone Release 1

Abstract

Abstract

To determine the site of action of various drugs which affect the release of prolactin (PRL) and growth hormone (GH), these drugs were infused into a hypophysial portal or jugular vein in anesthetized rats. When infused into a hypophysial portal vessel, L-dopa, a precursor of dopamine, significantly inhibited PRL release, whereas the dopamine antagonists, haloperidol and sulpiride, stimulated PRL release. In contrast, GH release was not significantly changed by any of these drugs. Infusion of substance P into a portal vessel caused an increase in both PRL and GH release. However, systemic infusion of haloperidol, sulpiride, and substance P in the same dose infused into a portal vessel failed to affect both PRL and GH levels. These findings suggest that PRL but not GH secretion is inhibited by a dopaminergic mechanism at least in part at the pituitary level, whereas substance P may stimulate both PRL and GH secretion at the pituitary level.