Angiotensin II (1-4), human is an endogenous peptide produced from AT I by angiotensin-converting-enzyme (ACE). Angiotensin II binds the AT II type 1 (AT1) receptor, stimulating GPCRs in vascular smooth muscle cells and increasing intracellular Ca2+ levels. Angiotensin II also acts at the Na+/H+ exchanger in the proximal tubules of the kidney.