Abstract
1. Micro-injections of a few nanograms of prostaglandin E(1) (PGE(1)) into the anterior hypothalamus of unanaesthetized cats produced a rise in rectal temperature, whereas temperature was not affected when micro-injections of even larger doses were made into the posterior hypothalamus. The hyperthermia produced by injections of PGE(1) into the cerebral ventricles is therefore attributed to an action of PGE(1) on the anterior hypothalamus.2. During a pentobarbitone sodium anaesthesia the sensitivity of cats to the hyperthermic effect of PGE(1) injected into the cerebral ventricles was found to be greatly reduced, particularly during the early stage of anaesthesia when body temperature was falling steeply.