Nursing Pharmacology: Autonomic Pharmacology Adrenergic Drugs
Besides reuptake and diffusion away from receptor sites, catecholamine action can end due to metabolic transformation.
Two primary catecholamine degrading enzymes:
Monoamine Oxidase (MAO)
Catechol-O-Methyl Transferase (COMT)
Inhibitors of MAO, such as phenelzine (Nardil), and tranylcypromine (Parnate) increase norepinephrine, dopamine, and serotonin (5-HT) brain concentrations.
These concentration increases may be responsible for antidepressant action of MAO inhibitors.
About 25% of circulating norepinephrine is extracted during a single passage through the lungs.
About 20% of clinical dopamine doses are cleared by the lung, although there is minimal dobutamine extraction, an exception.
Epinephrine is not extracted: same concentration arterial & venous blood
Inhaled anesthetics may interfere with the pulmonary amine transport system required for norepinephrine transport into pulmonary cells.
Hoffman, B.B and Lefkowitz, R.J, Catecholamines, Sympathomimetic Drugs, and Adrenergic Receptor Antagonists, In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics, (Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp.232-242.
Stoelting, R.K., "Sympathomimetics", in Pharmacology and Physiology in Anesthetic Practice, Lippincott-Raven Publishers, 1999, pp. 293-301