Effects of prostaglandin E1, E2 and E2 alpha on isolated pial arteries of cat

Responses to prostaglandin (PG), E1, E2, and F2 alpha were studied on isolated feline middle cerebral arteries. At resting state PGF 2 alpha produced strong dose-dependent contractions. PGE2 elicited weak relaxations at low concentrations, followed by powerful contractions at higher doses. PGE1 had little effect on resting pial vessels. The relative constrictory potency was PGF2 alpha greater than PGE2 greater than PGE1. During active tone, induced by administration of either potassium, norepinephrine, or 5-hydroxytryptamine, relaxations induced by PGE1 were enhanced, whereas PGE2-induced relaxations were unaffected. PGE1-induced relaxations were more pronounced when the active tension had been produced by administration of PGF2 alpha than with either of the vasoactive amines or potassium. This study demonstrates the importance of smooth muscle tone, and by what means this is achieved, when examining the response of PG's on cerebral blood vessels.