An Indirect Evaluation of the Effect of the Autonomic Nervous System Following Converting Enzyme Inhibition in Hypertension

Common carotid blood flow and cold pressor test were evaluated in 16 patients with sustained essential hypertension before and after 30 days treatment with the converting enzyme inhibitor Enalapril (20 mg). Enalapril decreased blood pressure and carotid vascular resistance with no significant change in heart rate. After treatment, despite a wide range of the responses, the changes in systolic blood pressure to cold test were significantly attenuated, whereas the heart rate responses were not. Acute random and double blind administration of either Cadralazine or Nitrendipine, two vasodilating drugs which are known to cause an activation of the autonomic nervous system, were performed before and after long term treatment by Enalapril. Whereas the blood pressure and heart rate responses to cold test was unmodified by these compounds before Enalapril treatment, significant changes were observed after converting enzyme inhibition: Cadralazine reduced the heart rate response whereas Nitrendipine increased it significantly. The study provides evidence that converting enzyme inhibition causes sympatho-inhibitory influences which are principally observed in stress conditions, with heterogeneous responses depending on the nature and the type of stimulation.