Alpha-adrenoceptor blockers selective

Alpha-adrenoceptor antagonists. Prazosin, afluzosin, indoramin, terazosin and doxazosin are all a-adrenoceptor blockers, with selectivity for the a -subtype. They cause significant increases (compared to placebo) in objective measures such as maximal... 

E. Adrenoceptor Blockers Alpha -selective agents (eg, prazosin) and beta-blockers (eg, propranolol) are effective antihypertensive drugs. Alpha-blockers reduce vascular resistance and venous return. The nonselective alpha-blockers (phentolamine, phenoxybenzamine) are of no value in chronic hypertension because of excessive compensatory responses, especially tachycardia. Alpha,-selective adrenoceptor blockers are relatively free of the severe adverse effects of the nonselective alpha-blockers and postganglionic nerve terminal sympathoplegic agents. 

Indoramin is a postsynaptic selective alphai-adrenoceptor antagonist that is chemically distinct from the quinazo-lines. Unlike some other alpha-blockers, indoramin lowers blood pressure without a resulting reflex tachycardia or postural hypotension (1). However, it has largely been supplanted by more modern drugs, such as doxazosin, prazosin, and terazosin. 

Answer B. Propranolol is a nonselective blocker of beta adrenoceptors, whereas meto-prolol is Pj -selective. Metoprolol is less likely to block receptors in the bronchiolar smooth muscle and is less likely to cause bronchoconstriction, especially in asthmatic patients. Propranolol and metoprolol are considered to be equally effective as antiarrhythmics and in post-MI prophylaxis, and both are cardiodepressant. Drugs that appear to have both alpha- and beta-blocking actions include carvedilol and labetalol. 

---