DIFFERENTIAL EFFECTS OF PROSTAGLANDINS E₁, E₂, F₁ AND F₂ ON ADRENERGIC VASOCONSTRICTION IN THE DOG HINDPAW

¹ Department of Pharmacology, College of Medicine, University of Iowa, Iowa City, Iowa

The influence of i.a. infusions of equivalent doses of prostaglandins (PG) E₁, E₂, F₁ and F₂ on vasoconstrictor responses to norepinephrine and sympathetic nerve stimulation were evaluated in the dog hindpaw perfused at constant flow. Infusions of PGE₁ and PGE₂,1 µg/min, decreased vascular resistance in the hindpaw. PGE₁ markedly reduced responses to i.a. norepinephrine, angiotensin and sympathetic nerve stimulation whereas PGE₂ did not alter these responses. However, when the infusion rate was increased to 2 µg/min, responses to nerve stimulation, but not norepinephrine, were enhanced. Infusion of PGF₁, and PGF₂, 1 µg/min, caused no change in vancular resistance in the hindpaw but enhanced the response to sympathetic nerve stimulation. PGF₁, decreased the response to norepinephrine whereas PGF₂, was without effect. These results suggest that PGF₂ may enhance adrenergic transmission in the hindpaw by facilitating the release of transmitter from sympathetic nerve endings and that PGE₁ may decrease the sensitivity of the cutaneous vessels to norepinephrine by a nonspecific effect. These data provide further support for the postulate that, by a variety of mechanisms, prostaglandins may serve as modulators of adrenergic responses in vascular smooth muscle.