Irbesartan is a highly potent and specific angiotensin II type 1 (AT1) receptor antagonist with IC50 of 1.3 nM.Target: Angiotensin ReceptorIrbesartan treatment markedly induces the expression of the adipogenic marker gene adipose protein 2 (aP2) in 3T3-L1 cells in a concentration-dependent manner with EC50 of 3.5 μM and 3.3-fold induction at the concentration of 10 μM. Irbesartan (10 μM) markedly induces transcriptional activity of the peroxisome proliferator–activated receptor-γ (PPARγ) by 3.4-fold independent of its AT1 receptor blocking action. Pretreatment with Irbesartan (~10 μM) decreases angiotensin II-induced apoptosis in rat vascular smooth muscle cells by blocking angiotensin II internalization in a concentrationdependent manner. Oral administration of Irbesartan (1 mg/kg) reduces angiotensin II (AII)-induced hypertension, equipotent with losartan in conscious normotensive rats, markedly more active than losartan (10 mg/kg) in normotensive cynomolgus monkeys. Administration of Irbesartan (7 mg/kg/day) significantly prevents skeletal muscle apoptosis and muscle atrophy in rats with monocrotaline-induced congestive heart failure (CHF), which is involved with the decrease of TNFα level and attributed to AT1 receptor blocking.