Dilatation and constriction of rat gastric mucosal microvessels through prostaglandin EP2 and EP3 receptors

Background: Prostaglandin (PG)E-2 has both a vasodilating action and a prot ective function in the gastric mucosa. There are four subtypes of PGE(2)-se nsitive, or EP, receptors. Aim: To identify the subtype of EP receptors in the microvessels of the rat gastric mucosa using EP2 and EP3 receptor agonists. Methods: The posterior wall of the anaesthetized rat stomach was secured in a chamber and superfused with Tyrode's solution, and the gastric microcirc ulation of the mucosal base was observed through a window with transillumin ation, PGE(2) and its derivatives (20 mu L) were applied topically in the w indow. Results: PGE(2) (0.001-10 mu mol/L), misoprostol (EP2/EP3 receptor agonist; 0.01-100 mu mol/L) and butaprost (EP2 receptor agonist: 1-1000 mu mol/L) d ilated the arterioles dose-dependently, but M&B 28 767 (EP3 receptor agonis t; 0.001-10 mu mol/L) did not alter their diameters, M&B 28 767 constricted the venules and collecting venules dose-dependently whereas butaprost dila ted them. PGE(2) and misoprostol had bell-shaped dose-response curves: cons triction by low doses of PGE(2) and misoprostol (0.001-0.1 mmol/L and 0.01- 1 mu mol/L) and dilation by high doses of PGE(2) and misoprostol (0.1-100 m u mol/L and 1-100 mu mol/L). Conclusions: These results suggest that PGE(2) dilated both arterioles and venules in the rat gastric mucosa through the EP2 receptors and constricted the venules through the EP3 receptors.