T-lymphocyte and plasma angiotensin-converting enzyme activity during enalapril and losartan administration in humans

This study evaluated the long-term effects of the angiotensin-converting enzyme inhibitor enalapril and the angiotensin II type I receptor antagonist losartan on the angiotensin-converting enzyme activity in T lymphocytes and plasma in patients with essential hypertension. The study was a randomized, placebo-controlled. double-blind, crossover design. Nine patients with sitting blood pressure greater than or equal to 95 mm Hg and less than or equal to 105 mm Hg at the end of a 4-week placebo run-in period entered the double-blind phase of the study, which consisted of three 6-week periods during which patients were treated with placebo, enalapril (20 mg, once daily), or losartan (50 mg, once daily) The angiotensin-converting enzyme activity in T lymphocytes was measured as the activity of the degradation of the substrate Hippuryl-His-Leu and as the appearance of the dipeptide His-Leu, which was quantified spectrofluorometrically. Enalapril but not losartan suppressed (p less than or equal to 0.01) the angiotensin-converting enzyme activity in plasma. whereas it stimulated (p less than or equal to 0.05) the angiotensin-converting enzyme activity in circulating T lymphocytes. Our data document induction of angiotensin-converting enzyme in human T lymphocytes during long-term treatment with the angiotensin-converting enzyme inhibitor enalapril. Angiotensin II receptor type 1 antagonism with losartan had no effect on plasma or lymphocytic angiotensin-converting enzyme.