Angiotensin-II formed from angiotensin-I in a reaction catalyzed by angiotensin-converting enzyme (ACE), is a potent vasoconstrictor, the primary vasoactive hormone of the renin-angiotensin system and an important component in the pathophysiology of hypertension. It also stimulates aldosterone secretion by the adrenal cortex. Olmesartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin-II by selectively blocking the binding of angiotensin-II to the AT 1 receptor found in many tissues (e.g. vascular smooth muscle, adrenal gland). In-vitro-binding studies indicate that Olmesartan is a reversible & competitive inhibitor of AT 1 receptor. Olmesartan does not inhibit ACE (kinase-I, the enzyme that converts angiotensin-I to angiotensin-II and degrades bradykinin).