Prolactin and Zinc Effects on Rat Vascular Reactivity: Possible Relationship to Dihomo-γ-Linolenic Acid and to Prostaglandin Synthesis*

Ovine PRL at low concentrations potentiated pressor responses to norepinephrine and angiotensin in an isolated perfused rat mesenteric vascular preparation. Higher concentrations inhibited these pressor responses. Pressor responses to potassium which depend on extracellular calcium entry into the muscle were unaffected by PRL at any concentration. Either cortisol or lithium could completely block the PRL effect. Dihomo-gamma-linolenic acid (DHGL) and prostaglandin E1 had effects similar to those of PRL in that they potentiated norepinephrine responses at low concentrations, inhibited at high ones, and had no effect on potassium responses. Arachidonic acid and prostaglandin E2 potentiated both norepinephrine and potassium responses and had no inhibitory effects at high concentrations. Neither lithium nor cortisol blocked the effects of DHGL or arachidonic acid. Zinc had actions similar to those of PRL and DHGL, but which could be blocked only by lithium and not by cortisol. These results are consistent with the concept that PRL increases synthesis of the 1 series of prostaglandins by mobilizing DHGL. They provide further evidence that zinc may play a role in some actions of PRL.