PHAR 200 Study Guide - Midterm Guide: Tachycardia, Endocardium, Hypotension
Document Summary
Adenosine binds to p1 purinergic receptors that open g-protein regulated potassium channels. Given rapidly as a bolus, it inhibits sa nodal, atrial and av nodal conduction and is used to terminate many supraventricular arrhythmias. Magnesium sulfate given intravenously has been used to treat digoxin related arrhythmias and drug induced torsades de pointes. It is also used against arrhythmias due to hypomagnesemia. In all be the last case, the mechanism is uncertain. Nitroglycerin and isosorbide dinitrate are powerful smooth muscle relaxants. Both of these agents cause an increase in nitric oxide (no) in smooth muscle cells. No activates guanylyl cyclase to catalyze the synthesis of cgmp, which eventually leads to dephosphorylation of myosin light chains and subsequent smooth muscle relaxation. Veins are most sensitive to the nitrates, then arteries, followed by arterioles and precapillary sphincters. Increased venous capacitance leads to decreased ventricular filling pressure. All of these effect conspire to dramatically reduce cardiac work.
