Body temperature responses in cats and rabbits to the monoamine oxidase inhibitor tranylcypromine

Abstract

In unanesthetized cats tranylcypromine (1-10 mg/kg) had scarcely any effect on rectal temperature when injected intraperitoneally, yet such injections pre-vented the deep and long-lasting fall in rectal temperature which normally occurs when the cat is anesthetized by intraperitoneal pentobarbital sodium or intravenous chloralose. The anesthesia itself, however, was not affected. In some of the experiments with pentobarbital sodium rectal temperature even rose to fever level. In anesthetized and unanesthetized cats injections of tranylcypromine (0. 1-1 mg) into the cerebral ventricles caused a rise in rectal tempera-ture. In rabbits, rectal temperature was scarcely affected when surgi-cal anesthesia was produced by intravenous infusions of pentobarbital sodium under the same condition in which, in cats, intraperitoneal pentobarbital sodium produced a deep and long-lasting fall in tempera-ture, i. e. when no external heat was applied but excessive, dissipation of heat was prevented by placing the rabbit on a cotton-wool pad. However, when it was placed on the metal surface of an operating table, the anesthesia was associated with a deep fall in rectal tempera-ture. In anesthetized and unanesthetized rabbits tranylcypromine had no effect on rectal temperature when injected intraperitoneally (10 mg/kg) or into the cerebral ventricles (1 mg). These results are dis-cussed in relation to the theory that the 3 monoamines in the hypo-thalamus, 5-hydroxytryptamine (5-HT), adrenaline and noradrenaline [epinephrine-norepinephrine], act as central transmitters in tempera-ture regulation.