Adrenergic alpha1-Agonists

Alpha-1 adrenoceptors are G protein-coupled receptors for the catecholamines noradrenaline and adrenaline. They signal through the Gq/G11 family, stimulating the phosphatidylinositol-calcium pathway so that calcium is released from intracellular stores and protein kinase C is activated - the sequence that makes vascular smooth muscle contract. Drugs in this class bind and activate an alpha-1 receptor, reproducing that catecholamine effect; a drug belongs here because it switches the receptor on rather than blocking it.