Altered plasma leucine-enkephalin concentrations in patients with established hypertension may be involved in impaired regulation of blood pressure.

Leucine-enkephalin is known to modulate cardiovascular activity. In the present study we determined plasma leucine-enkephalin and noradrenaline concentrations in young men with essential hypertension and in normotensives at rest and after bicycle exercise. The essential hypertensive patients had a lower concentration level of resting leucine-enkephalin than the normotensives. Exercise increased leucine-enkephalin in both groups. Noradrenaline was significantly higher in the essential hypertensives than in the normotensives. The central alpha 2-agonist clonidine reduced leucine-enkephalin at rest in the normotensives and prevented its increase during exercise, but had no effect on leucine-enkephalin in the essential hypertensives. These results may reflect an altered interaction between leucine-enkephalin and noradrenaline in essential hypertensives compared to normotensives, possibly contributing to hypertension.