Indication for the treatment of symptomatic bph and mild to moderate hypertension.mechanism of action in general, a1-adrenergic receptors mediate contraction and hypertrophic growth of smooth muscle cells. a1-receptors are 7-transmembrane domain receptors coupled to g proteins, gq/11. three a1-receptor subtypes, which share approximately 75% homology in their transmembrane domains, have been identified: a1a (chromosome 8), a1b (chromosome 5), and a1d (chromosome 20). terazosin is the first a1-receptor antagonist to demonstrate selectivity for the a1a-receptor. all three receptor subtypes appear to be involved in maintaining vascular tone. the a1a-receptor maintains basal vascular tone while the a1b-receptor mediates the vasocontrictory effects of exogenous a1-agonists. activation of a1-receptors activates gq-proteins, which results in intracellular stimulation of phospholipases c, a2, and