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

Area of Science:

• Cardiovascular Pharmacology
• Immunopharmacology
• Hypertension Research

Background:

• The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in blood pressure regulation.
• Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor antagonists (ARBs) are key antihypertensive medications targeting the RAAS.
• The effects of these drugs on ACE activity within specific immune cells, like T lymphocytes, are not fully understood.

Purpose of the Study:

• To investigate the long-term impact of enalapril (an ACE inhibitor) and losartan (an ARB) on ACE activity.
• To compare ACE activity in both plasma and circulating T lymphocytes in patients with essential hypertension.
• To determine if enalapril or losartan differentially affect ACE activity in immune cells versus plasma.

Main Methods:

• Randomized, placebo-controlled, double-blind, crossover study involving nine patients with essential hypertension.
• Patients received placebo, enalapril (20 mg/day), or losartan (50 mg/day) for 6-week periods.
• ACE activity was measured in plasma and T lymphocytes by quantifying substrate degradation and dipeptide formation using spectrofluorometry.

Main Results:

• Enalapril significantly suppressed plasma ACE activity (p < 0.01).
• Conversely, enalapril significantly stimulated ACE activity in circulating T lymphocytes (p < 0.05).
• Losartan demonstrated no significant effect on ACE activity in either plasma or T lymphocytes.

Conclusions:

• Long-term treatment with the ACE inhibitor enalapril induces ACE activity in human T lymphocytes.
• This induction occurs despite suppression of plasma ACE activity.
• Angiotensin II receptor type 1 antagonism with losartan does not alter ACE activity in plasma or T lymphocytes.