URETHANE AND CONTRACTION OF VASCULAR SMOOTH MUSCLE

Abstract

In vitro studies were undertaken on rat aortic strips and portal vein segments in order to determine whether or not the anaesthetic, urethane, can exert direct actions on vascular smooth muscle. Urethane was found to inhibit development of spontaneous mechanical activity. This action took place with a urethane concentration as little as one tenth of that found in anaesthetic plasma concentrations, i.e., 10⁻³ m. Urethane (10⁻³ to 10⁻¹ m) dose‐dependently attenuated contractions induced by adrenaline, angiotensin and KCl. These inhibitory actions were observed with urethane added either before or after the induced contractions. Ca²⁺‐induced contractions of K⁺‐depolarized aortae and portal veins were also attenuated, dose‐dependently, by urethane. All of these inhibitory effects were completely, and almost immediately, reversed upon washing out the anaesthetic from the organ baths. A variety of pharmacological antagonists failed to mimic or affect the inhibitory effects induced by urethane. These data suggest that plasma concentrations of urethane commonly associated with induction of surgical anaesthesia can induce, directly, relaxation of vascular muscle.