SYMPATHOMIMETIC DRUG (Epinephrine)
The smooth muscle of blood vessels that supply skeletal muscles has both beta-2 and alpha receptors; activation of beta-2 receptors causes vasodilation, and stimulation of alpha receptors constricts these vessels. In such vessels, the threshold concentration for activation of beta-2 receptors by Epinephrine is lower than that for alpha receptors, but when both types of receptors are activated at high concentrations of Epi, the response to a receptors predominates; physiological concentrations of Epi primarily cause vasodilation. The integrated response of an organ to sympathomimetic amines results not only from their direct effects, but also from reflex homeostatic adjustments. when a drug (e.g., a beta-2 agonist) lowers mean blood pressure at the mechanoreceptors of the carotid sinus and aortic arch, the baroreceptor reflex works to restore pressure by reducing parasympathetic (vagal) outflow from the CNS to the heart, and increasing sympathetic outflow to the heart and vessels. Conve...