Losartan Carboxylic Acid (E-3174), an active carboxylic acid metabolite of Losartan, is an angiotensin II receptor type 1 (AT1) antagonist. The Ki values are 0.97, 0.57, 0.67 nM for rat AT1B/AT1A and human AT1, respectively. Losartan Carboxylic Acid blocks the angiotensin II-induced responses in vascular smoothmuscle cells (VSMC). Losartan Carboxylic Acid elevates plasma renin activities and reduces mean arterial pressure.