title: Biphasic response of circular muscle to prostaglandin E2 in guinea-pig colon.
abstract: The effects of prostaglandin E2 (PGE2) on mechanical and electrical activities of the colonic circular muscle strip of guinea-pig were examined. PGE2, at doses over 10(-7) M, produced an initial contraction, followed by a relaxation, while PGF2 alpha (10(-6) M) produced a tonic contraction. The biphasic response of circular muscle strip to PGE2 was not influenced by atropine, tetrodotoxin, propranolol and indomethacin. PGE2 (10(-6) M) initially increased spike discharges, followed by their inhibition in the colonic circular muscle strip. Verapamil (10(-5) M) blocked PGE2-induced initial contraction but did not block the following relaxation. At low temperature (22 degrees C-27 degrees C) and in the presence of tetraethylammonium (5 x 10(-3) M), PGE2 (10(-6) M) produced a contractile response without showing any relaxation. The present results suggest that PGE2-induced initial contraction may depend on an increase in spike discharges and that the following relaxation may depend on an increase in K-ion permeability in the colonic circular muscle. The reason why PGE2 showed a biphasic response on the colonic circular muscle strip is considered to be a summation of rapid small contraction and of late large relaxation.
authors.affiliation: Laboratory of Physiology, School of Allied Health Professions, Sapporo Medical College, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ishizawa
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D003080:Cold Temperature; D003106:Colon / Q000187:drug effects; D015237:Dinoprost / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology*; D004594:Electrophysiology; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D001285:Atropine; D011433:Propranolol; D015237:Dinoprost; D014700:Verapamil; D015232:Dinoprostone; D007213:Indomethacin