Atropine is a muscarinic antagonist that is used to treat atrioventricular heart block, bradycardia and for organophosphate anticholinesterase/pesticides poisoning. Atropine is an alkaloid originating from the plant Atropa Betalldonna and can be found in some other plants. Naturally it is a racemic mixture of equal parts d-hyoscyamine and l-hyoscyamine. Althought is is classified as a muscarinic antagonist it is more commonly classified as an anti-cholinergic or an antiparasympathetic drug. Sufficient doses of atropine will inhibit carious types of reflex vagal cardiac asystole as well as bradycardia and asystole produced by choline esters, anticholinesterase agents, parasympathomimetic drugs or cardiac arrest produced by vagus nerve stimulation. It is also possible that atropine may lessen the degree of partial heart block if vagal activity is the etiological (causing or contributing) factor. In clinical dose administrations it counteracts the peripheral dilation and low blood pressure produced by choline esters. If it given by itself it does not exert a large or even effect on blood vessels and/or blood pressure. Atropine binds to and inhibits muscarinic acetylcholine receptors which produces a large range of anticholinergic effects. In the heart (the main use for atropine) muscarinic 2 receptors (M2) receptors reside in the SA and VA node in the atria and ventricles respectively are affected by atropine. Atropine inhibits the binding of acetylcholine and other choline esters causing an inhibitory effect increasing the concentration of cAMP produced. Higher cAMP concentration promote action potentials in the cells as well as increasing calcium influx from membrane channels. All of these downstream effects increase heart rate and blood pressure therefore abolishing bradycardia and low blood pressure. Atropine is administered in an intravenous, endotracheal, intramuscular, or intramedullary injection or subcutaneously.

Atropine M2 Cardiac Muscle Contraction Pathway References