Angiotensin II is a naturally occurring octapeptide hormone component of the renin-angiotensin-aldosterone system (RAAS) and is a potent vasoconstrictor. Angiotensin II has important roles in cardiovascular, neurologic, and renal physiology, including maintenance of blood pressure, thirst sensation, response to the baroreceptor reflex, determination of renal blood flow and glomerular filtration rate, and electrolyte and free water homeostasis.