On what receptors are the sympathetic amines active, and what is their effect?

Sympathetic amines exert effects on four different receptors:

Alpha-receptors provoke vasoconstriction of peripheral arteries when stimulated.

Beta-receptors increase atrial and ventricular contraction, increase heart rate by stimulating the sinus node, and enhance AV conduction.

Beta2-receptors promote bronchodilation and vasodilation.

Dopaminergic receptors, found in various tissues including blood vessels and nervous system tissues, are of two types: The activation of dopamine-1 receptors causes vasodilation in coronary, renal, mesenteric, and cerebral vascular beds, by stimulating adenylate cyclase and increasing cAMP. The activation of dopamine-2 receptors causes vasodilation, but by inhibiting transmission of sympathetic nerve endings.

What amines are alpha or beta selective?

Isoproterenol has practically no alpha-stimulating effect, with relatively pure beta-stimulation. It is clinically valuable in stimulating the sinus node and enhancing AV conduction in bradyarrhythmias. Its limitation in this setting is its hypotensive effect through its betaj properties.

Methoxamine is a practically a pure alpha-stimulant, helpful in hypotension in the cardiac catheterization laboratory.

Norepinephrine is predominantly alpha- and beta-stimulant and is valuable in cardiogenic shock following bypass surgery for stunned myocardium, and in hypotension.

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