Dilatation and constriction of rat gastric mucosal microvessels through prostaglandin EP2and EP3receptors

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Abstract
Prostaglandin (PG)E2 has both a vasodilating action and a protective function in the gastric mucosa. There are four subtypes of PGE2-sensitive, or EP, receptors. To identify the subtype of EP receptors in the microvessels of the rat gastric mucosa using EP2 and EP3 receptor agonists. The posterior wall of the anaesthetized rat stomach was secured in a chamber and superfused with Tyrode's solution, and the gastric microcirculation of the mucosal base was observed through a window with transillumination. PGE2 and its derivatives (20 microL) were applied topically in the window. PGE2 (0.001-10 micromol/L), misoprostol (EP2/EP3 receptor agonist; 0.01-100 micromol/L) and butaprost (EP2 receptor agonist; 1-1000 micromol/L) dilated the arterioles dose-dependently, but M&B 28 767 (EP3 receptor agonist; 0.001-10 micromol/L) did not alter their diameters. M&B 28 767 constricted the venules and collecting venules dose-dependently whereas butaprost dilated them. PGE2 and misoprostol had bell-shaped dose-response curves: constriction by low doses of PGE2 and misoprostol (0.001-0.1 micromol/L and 0.01-1 micromol/L) and dilation by high doses of PGE2 and misoprostol (0.1-100 micromol/L and 1-100 micromol/L). These results suggest that PGE2 dilated both arterioles and venules in the rat gastric mucosa through the EP2 receptors and constricted the venules through the EP3 receptors.

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