Direct-acting arteriolar vasodilators

Diazoxide [dye az OX ide] is a direct-acting arteriolar vasodilator. It has vascular effects like those of hydralazine. For patients with coronary insufficiency, diazoxide is administered intravenously with a p-blocker, which diminishes reflex activation of the heart. Diazoxide is useful in the treatment of hypertensive emergencies, hypertensive encephalopathy, and eclampsia. Excessive hypotension is the most serious toxicity. 

Direct-acting arteriolar vasodilators relax the smooth muscles of the blood vessels, causing vasodilation, which results in an increase in blood flow to the brain and kidneys. Direct-acting arteriolar can be combined with diuretics to decrease the edema. 

MDL 899 (26) is a direct acting arteriolar vasodilator in man, but coadministration of a beta-blocker is necessary to prevent reflex-related side effects. A clinical study with cadralazlne (ISF 2469, 27) shows this compound similar to hydralazine with fewer side effects. Two other vasodilators, budralazine (28) and pinacidil (29) may owe some of their activity to calcium channel blockade.Anthranilamlde (WIN 48,049) lowers blood pressure in monkeys without accompanying tachycardia. This compound acts primarily as a direct vasodilator but also has sympatholytic and dopaminergic activities. Compounds and 32 also lower blood pres-... 

Fast (Sodium) Channel Blocker I Direct-Acting Arteriolar Vasodilators... 

Pharmacology Minoxidil is a direct-acting peripheral vasodilator. Minoxidil elicits a reduction of peripheral arteriolar resistance. The exact mechanism of action on the vascular smooth muscle is unknown. 

The answer is d. (Hardman, pp 794-795.) Hydralazine, minoxidil, diazoxide, and sodium nitroprusside are all directly acting vasodilators used to treat hypertension. Because hydralazine, minoxidil, nifedipine, and diazoxide relax arteriolar smooth muscle more than smooth muscle in venules, the effect on venous capacitance is negligible. Sodium nitroprusside, which affects both arterioles and venules, does not increase cardiac output, a feature that enhances the utility of sodium nitroprusside in the management of hypertensive crisis associated with MI. 

Direct-acting vasodilators lower the peripheral vascular resistance mainly by causing arteriolar dilation. Drugs discussed are nitroprusside, hydralazine, minoxidil, and diazoxide. 

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