Cardiovascular effects of a potent opioid peptide, (D-Met2, Pro5)-enkephalinamide.

The cardiovascular effects of morphine and a potent enkephalin analogue, D-Met2, Pro5-enkephalinamide (D-Met2, Pro5-EA) have been examined in pentobarbitone anesthetized cats with their vagi cut and in awake normotensive and genetically hypertensive rats. In cats both opioids only moderately decreased the blood pressure and the heart rate, but the enkephalin analogue considerably attenuated the carotid occlusion pressor response. Neither substance influenced the blood pressure and the heart rate in normotensive rats, but both induced moderate hypotension and considerable bradycardia in spontaneously hypertensive rats, the potency of D-Met2, Pro5-EA being much stronger than that of morphine. These observations confirm the conclusions from the literature that, under physiological conditions, endorphins play no primary role in the regulation of the cardiovascular functions but they might be mobilized in certain cases of pathological elevation of the blood pressure probably as a part of a compensatory process.