Losartan Carboxylic Acid (E-3174), an active carboxylic acid metabolite of Losartan, is an angiotensin II receptor type 1 (AT1) antagonist. The K_i 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^[1][2][3][4]. IC50 & Target: Angiotensin II receptor type 1^[1] In Vitro: The specific binding of [125I]-angiotensin II to VSMC is inhibited by Losartan Carboxylic Acid (E-3174) with an IC₅₀ of 1.1 nM. Losartan Carboxylic Acid abolishes the angiotensin II-induced formation of inositolphosphates in VSMC. Losartan Carboxylic Acid inhibits the angiotensin II-induced elevation of intracellular cytosolic Ca2+ concentration with an IC₅₀ of 5 nM. Losartan Carboxylic Acid is more effective than losartan in blocking the angiotensin II-induced increase in Egr-1 mRNA. Losartan Carboxylic Acid inhibits the angiotensin II-induced cell protein synthesis with an IC₅₀ of 3 nM^[1]. In Vivo: Losartan Carboxylic Acid (E-3174) (0.1 mg/kg; i.v. followed by 0.02 mg/kg/h for 5.5 h) induces a similar level of inhibition (87±4%) of the pressor responses to angiotensin I^[3].
Intravenous Losartan Carboxylic Acid (0.1 mg/kg+0.01 mg/kg/min) is infused in anesthetized dogs with recent (8.1±0.4 days) anterior myocardial infarction. Electrolytic injury of the left circumflex coronary artery to induce thrombotic occlusion and posterolateral ischemia is initiated 1 h after the start of treatment^[4].