Terazosin

In general, __-adrenergic receptors mediate contraction and hypertrophic growth of smooth muscle cells. __-Receptors are 7-transmembrane domain receptors coupled to G proteins, Gq/__. Three __-receptor subtypes, which share approximately 75% homology in their transmembrane domains, have been identified: __A (chromosome 8), __B (chromosome 5), and __D (chromosome _0). Terazosin is the first __-receptor antagonist to demonstrate selectivity for the __A-receptor. All three receptor subtypes appear to be involved in maintaining vascular tone. The __A-receptor maintains basal vascular tone while the __B-receptor mediates the vasocontrictory effects of exogenous __-agonists. Activation of __-receptors activates Gq-proteins, which results in intracellular stimulation of phospholipases C, A_, and D. This results in mobilization of Ca_+ from intracellular stores, activation of mitogen-activated kinase and PI_ kinase pathways and subsequent vasoconstriction. Terozosin produces its pharmacological effects by inhibiting __A-receptor activation. Inhibition of these receptors in the vasculature and prostate results in muscle relaxation, decreased blood pressure and improved urinary outflow in symptomatic benign prostatic hyperplasia.