Libenzapril is a long-acting, small polar angiotensin-converting enzyme (ACE) inhibitor with antihypertensive activity. Libenzapril competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstrictive actions of angiotensin II and results in vasodilation. Libenzapril also decreases angiotensin II-induced aldosterone secretion by the adrenal cortex, which leads to an increase in sodium excretion and subsequently increases water outflow. Both libenzapril and water transport was found to be significantly higher (about two- to five-fold) in six of the seven different brain regions in hypertensive rats as compared to the normotensive controls.