Angiotensin II (AngII) elicits multiple responses in a variety of tissues, including both short- and long-term effects such as contraction of smooth muscle and mesangial cells, stimulation of aldosterone secretion from the adrenal cortex, facilitation of norepinephrine release from nerve endings, stimulation of sodium reabsorption in the renal proximal tubules, inhibition of renin release from the juxtaglomerular cells, induction of hypertrophy of cardiac myocytes and vascular smooth muscle cells. The AngII receptor has never been isolated in a pure and stable form because it is one of the most unstable receptors when solubilized from plasma membrane by detergents. Thus, it was not clear whether the multiple responses elicited by this peptide hormone are mediated by different types of the receptor or a single-type receptor. The AT₁ receptor is implicated for practically all the harmful effects of AngII as it has been shown that practically all the hypertensinogenic and mitogenic effects of AngII can be blocked by losartan.