Influence of thyrotropin releasing hormone (TRH) on drug-induced narcosis and hypothermia in rabbits.

Thyrotropin releasing hormone (TRH) administered via the intracerebroventricular (icv) route in doses ranging between 0.1 and 100 mug decreased the duration of pentobarbital-induced narcosis in rabbits. Antagonism of narcosis occurred whether TRH was administered before or after the barbiturate. TRH doses above 10 mug produced, in addition, behavioral excitation and hyperthermia. The antagonism of phenobarbital-induced narcosis was not as profound; animals were aroused only for a short period of time, after which the narcotized state returned. However, TRH exerted a prolonged antagonism or reversal of the phenobarbital-induced hypothermia. The central nervous system depression and analgesia produced by morphine were unaffected by TRH, but hypothermia and respiratory depression were reversed. TRH may represent an arousal factor in mammalian brain.