Plasma levels of beta-endorphin, leucine enkephalin and arginine vasopressin in patients with essential hypertension and the effects of clonidine.

In order to investigate the changes of endogenous opiate systems in hypertension and their possible role in the pathogenesis in hypertension, we measured plasma concentrations of beta-endorphin, leucine-enkephalin, neurotension, arginine vasopressin, plasma renin activity and angiotensin II by radioimmunoassay in 60 normal persons and 120 patients with essential hypertension. The results showed that the patient group had lower levels of beta-endorphin and leucine enkephalin (P < 0.001), higher levels of arginine vasopressin, plasma renin activity and angiotensin II (P < 0.01, P < 0.05 and P < 0.05, respectively), and normal level of neurotensin, as compared with those in normal group. Plasma levels of leucine-enkephalin was correlated negatively to the mean artery pressure (r = -0.196, P < 0.05). Plasma level of arginine vasopressin was correlated to the duration of the hypertension (r = 0.216, P < 0.05). After 150 min and 14 days of treatment with clonidine, plasma levels of beta-endorphin, leucine-enkephalin increased significantly (< 0.01) and correlated negatively with the decrease of the mean artery pressure (r = -0.340 and r = -0.436 at 150 min, r = -0.369 and r = -0.441 on the 14th day, respectively, P < 0.01). Plasma renin activity and angiotensin II decreased significantly (P < 0.05 and P < 0.01). Arginine vasopressin and neurotensin did not change significantly. After intravenous administration of opiate antagonist-naloxone, the blood pressure and heart rate increased significantly (P < 0.01). The results suggested that the changes of endogenous opioids may be involved in the pathogenesis of hypertension and in the antihypertensive action of clonidine.