Cholinergic Antagonists HTN Flashcards
Muscarinic receptors in heart and affect
M2 receptors in SA Node (decelerates rate of firing) and Contractile myocytes (decreases atrial myocytes)
Muscarinic receptors in blood vessels
M2 and M3 in endothelium of vessels in heart, brain, viscera - synthesizes and releases EDRF
M2 receptor activation triggers:
inhibition of adenyl cyclase and decrease in cAMP resulting in activation of inward potassium channels and inhibition of vantage-gated calcium channels, causing hyper polarization and inhibition of neuronal activity
M3 receptor activation triggers:
increases in calcium and protein kinase C, leading tot eh synthesis and release of NO from the vascular endothelial cells
Where does acetylcholine act
The M2 and M4 auto receptors to cause direct effect; indirect effects caused by opposition of Beta 1 receptors and inhibition of NE release from sympathetic nervous system
Effects of Acetylcholine within CV system
Vasodilation, decreased heart rate, decreased AV node conduction velocity, and decreased force of atrial cardiac contraction
Cholinergic innervation of skeletal muscle:
there is none!
Atropine effects on heart
Low dose causes transient decrease in HR; progressive tachycardia with higher dose
Increases only the resting heart rate, not the maximal heart rate
Atropine effects on the circulatory system
counteracts the peripheral vasodilation and sharp fall in BP caused by choline esters
Given alone, atropine causes no significant effect on vessels; but in higher doses, can dilate cutaneous blood vessels, especially in the cheeks causing atropine flush
Atropine uses
abolishes reflex vagal cardiac slowing or systole from secondary causes; prevents or abolishes bradycardia caused by parasympathomimetic drugs or other means; facilitates AV conduction - shortens functional refractory period of AV node, helps with sinus/nodal brady or AV block
