The clinical uses of catecholamines are based on their actions on bronchial smooth muscle, blood vessels, and the heart. Epinephrine is also useful for the treatment of allergic reactions that are due to liberation of hista-mine in the body, because it produces certain physiological effects opposite to those produced by histamine. It is the primary treatment for anaphylactic shock and is useful in the therapy of urticaria, angioneurotic edema, and serum sickness.
Epinephrine also has been used to lower intraocular pressure in open-angle glaucoma. Its use promotes an increase in the outflow of aqueous humor. Because epinephrine administration will decrease the filtration angle formed by the cornea and the iris, its use is con-traindicated in angle-closure glaucoma; under these conditions the outflow of aqueous humor via the filtration angle and into the venous system is hindered, and intraocular pressure may rise abruptly.
The vasoconstrictor actions of epinephrine and nor-epinephrine have been used to prolong the action of local anesthetics by reducing local blood flow in the region of the injection. Epinephrine has been used as a topical hemostatic agent for the control of local hemorrhage. Norepinephrine is infused intravenously to combat systemic hypotension during spinal anesthesia or other hypotensive conditions in which peripheral resistance is low, but it is not used to combat the hypotension due to most types of shock. In shock, marked sympathetic activity is already present, and perfusion of organs, such as the kidneys, may be jeopardized by norepi-nephrine administration.
Dopamine is used in the treatment of shock owing to inadequate cardiac output (cardiogenic shock), which may be due to myocardial infarction or congestive heart failure. It is also used in the treatment of septic shock, since renal circulation is frequently compromised in this condition. An advantage of using dopamine in the treatment of shock is that its in-otropic action increases cardiac output while dilating renal blood vessels and thereby increasing renal blood flow.
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