title: Thrombin contracts isolated bovine retinal small arteries in vitro.
abstract: The effect of thrombin was tested in vitro on rings of bovine retinal small arteries (internal diameter approximately 200 microns). Cumulative addition of thrombin (0.001-10 units/ml) induced a variable concentration-dependent contraction of the retinal arteries. The contractions were slow in onset and reached a plateau after 5-8 minutes when thrombin was added cumulatively to the organ bath. Two vessels remained contracted greater than 1 hour after wash-out of thrombin. Maximum vessel contraction induced by thrombin was equal to 43% of the vessel Emax (1.36 N/m), with an effective concentration at the 50% level of 0.04 units/ml. Vessel contraction induced by 1 unit/ml of thrombin was, in contrast, transient, reaching a maximum within 2-4 minutes. Thereafter the vessel tension declined again almost back to baseline within the next 10-20 minutes. Contractions to thrombin could not be repeated nor could it be elicited with thrombin inactivated with heat or antithrombin-III. Treatment of vessels with 10(-6) M phenoxybenzamine had no effect on the thrombin-induced vessel response. These findings indicate that the contractile effect of thrombin depends on its catalytic activity. Indomethacin at a concentration of 10(-5) M did not affect the thrombin-induced vessel response. Methylene blue at a concentration of 3 X 10(-6) M potentiated the thrombin-induced response in the larger, greater than 200-microns diameter retinal arteries. The ensuing relaxation of the arteries, after maximal tone was reached, was slower than in the control.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, Aarhus University, Denmark.
authors.forename: N C
authors.initials: NC
authors.lastname: Nyborg
authors.forename: P J
authors.initials: PJ
authors.lastname: Nielsen
mesh_terms: D000818:Animals; D002196:Capillaries / Q000187:drug effects; D002417:Cattle; D004347:Drug Interactions; D004730:Endothelium, Vascular / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009638:Norepinephrine; D011188:Potassium / Q000494:pharmacology; D012161:Retinal Artery / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*; D014662:Vasoconstrictor Agents
chemical_list: D014662:Vasoconstrictor Agents; D012701:Serotonin; D006632:Histamine; D013917:Thrombin; D011188:Potassium; D009638:Norepinephrine; D007213:Indomethacin