Effects of beta-endorphin on the contraction and electrical activity of the isolated perfused rat heart.

beta-Endorphin at pharmacological doses reduced both the left ventricular systolic and diastolic pressures of the isolated rat heart. The reduction in the diastolic ventricular pressure was does dependent. Beta-Endorphin also altered the electrical activities of the isolated heart, disturbing the normal electrocardiogram pattern. The degree of disturbance was also dose dependent. Naloxone itself did not produce any effect. However it antagonized the depressant effects and completely abolished the effect of beta-endorphin on the electrical activity of the heart, indicating that beta-endorphin acts via the naloxone sensitive receptors. The results suggest a possible regulatory role of intracardiac endogenous opioid peptides in the cardiac functions.