ENALAPRIL DECREASES PLASMA NORADRENALINE LEVELS DURING THE COLD PRESSOR TEST IN HUMAN HYPERTENSIVES

1. The effects of the angiotensin‐converting enzyme (ACE) inhibitor enalapril on the responses of blood pressure and plasma catecholamine levels to the cold pressor test in human hypertensives were examined. 2. Systolic and diastolic blood pressure decreased significantly after treatment with enalapril (5 mg/ day for 4 weeks) as did the resting level of plasma noradrenaline. 3. The cold pressor test induced a rise in blood pressure and plasma noradrenaline levels. After 2 and 4 weeks enalapril treatment, the rises in the plasma noradrenaline level and systolic and diastolic pressure due to cold pressor test were reduced significantly. 4. These results suggest that ACE inhibition has a sympatho‐inhibitory effect. One possible explanation is that enalapril reduces angiotensin II formation thus decreasing the activation of release‐enhancing angiotensin II receptors on postganglionic sympathetic nerve endings.