We studied the effects of three various angiotensin converting enzyme inhibitors (enalapril, lisinopril and quinapril) on heart rhythm variability in anesthetized and immobilized rats. In all cases (except for quinapril in experiments on anesthetized animals), the preparations reduced the total rhythm variability and, according to spectrum analysis, increased activity of the parasympathetic autonomic nervous system to different degrees and decreased sympathetic tone. Quinapril and lisinopril produced the most pronounced influence on heart rhythm in anesthetized rats; enalapril was less potent in this respect. In immobilized animals, quinapril and enalapril showed the greatest activity and lisinopril the lowest. The more pronounced effect of quinapril both under anesthesia and during immobilization appears to be linked to the highest affinity of quinaprilat to circulatory and tissue compartments of the renin-angiotensin-aldosterone system.

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