Analgesia, catatonia and changes in core temperature induced by opiates and endorphins: a comparison

Abstract

Since the detection of met and leu-enkephalins as endogenous opiate receptor ligands (Hughes et al., 1975) several other endogenous opioids, or endorphins, have been discovered and many synthetic derivatives of such compounds have become available. There are many parallels between the pharmacological actions of the endorphins and the opiate alkaloids. Some studies, however, have indicated that differences not attributable to variations in pharmacokinetic pro­perties appear to exist not only between these two groups of compounds but also between individual opioid peptides (Bloom et al., 1976; Jacquet and Marks, 1976). Such differences might be expected, at least in part, to arise from actions at different types of opiate receptors (Martin et al., 1976; Lord et al., 1977). The purpose of the present study was, therefore, to compare the effects of a repre­sentative series of opioid peptides and opiate alkaloids on nociception, general motor behavior and body temperature. Results obtained during the measurement of body temperature prompted some preliminary investigations into the possible role of endorphins in stress-induced hyperthermia.