What is the primary mechanism of action for Losartan?

Losartan functions primarily through the antagonism of angiotensin II receptors, specifically the type 1 (AT1) receptors. By blocking these receptors, Losartan prevents the action of angiotensin II, a potent vasoconstrictor that contributes to increased blood pressure and fluid retention. This action results in vasodilation, reduced secretion of aldosterone, and diminished reabsorption of sodium in the kidneys, all of which can lead to lowered blood pressure and improved cardiovascular outcomes.

The effectiveness of Losartan as an angiotensin receptor blocker (ARB) illustrates its role in treating hypertension and protecting against heart failure, stroke, and renal disease progression, particularly in diabetic patients. This mechanism is distinct from drugs that inhibit ACE enzymes, which block the conversion of angiotensin I to angiotensin II. Moreover, while Losartan's effects on sodium and fluid balance may lead to enhanced renal excretion, this is a secondary consequence of its primary action on angiotensin II receptors, rather than a direct mechanism. Lastly, Losartan does not enhance sympathetic outflow, which would counteract its blood-pressure-lowering effects.