Effect of beta-endorphin and cold stress on heart noradrenalin levels in rats.

We investigated cardiac noradrenalin (NA) levels during stress (from cold and from swimming) and after i.p. administration of beta-endorphin. Cardiac NA levels were significantly increased by endorphin, 1.25 mg X kg-1, and decreased by 10 mg X kg-1. Beta-endorphin, 10 mg X kg-1, and cimetidine, 20 mg X kg-1, decreased cardiac NA to control levels in stressed animals. Naloxone given to stressed animals treated either with beta-endorphin or cimetidine elevated NA to control concentrations, but failed to restore NA to the elevated levels induced by stress. These results suggest endorphin involvement in enhanced NA levels in stress and a possible role of H2-receptors in this involvement.