Endorphin-induced hyperthermia: characterization of the exogenously and endogenously induced effects.

Abstract

Endorphins-like opiates-were found to increase temperature at very low doses and to decrease temperature at high doses. Not only the decreasing, but also the increasing effect on temperature, seems to be mediated through opiate receptors, since it proved to be antagonizable by naloxone and to be diminished in morphine-tolerant and-dependent animals. Like opiate-induced hyperthermia, both the pharmacological as well as the supposedly physiological increase in temperature induced by endorphins were strongly diminished in restrained animals. Hyperthermia induced by pyrogens, however, was not antagonizable by either naloxone or restraining of the animals. Maintenance of normal body temperature in animals being exposed to acute cold could not be disturbed by administration of naloxone. As a whole, such findings support the suggestion derived from our previous observation that physiologically induced naloxone-antagonizable hyperthermia may be a sensitive measure for endorphin release. However, endorphins although being potent hyperthermic modulators of temperature, do not seem to be directly involved in the central regulation of temperature. Instead, the physiologically induced increase in temperature by endorphins seems to represent some epiphenomenon of physiological events primarily initiated for physiological requirements other than the support of thermostability.