CVANS: Virtual Dog Laboratory

Pretreatment Results: atropine

Test	Control	atropine
ACh
CARB
CO
DMPP
EPI
HIST
ISO
McN
NE
PHE
PILO
TYR
VS

Atropine antagonizes muscarinic receptors.

ACh is blocked because muscarinic receptors on vascular endothelium are blocked by atropine. Apparently, the dose of ACh used was not high enough to express the nicotinic effects of ACh. Because ACh is less potent as a nicotinic agonist when injected systemically its nicotinic effects are generally not seen at low or medium doses of ACh.

CARB is reversed. This is because CARB has fairly prominent nicotinic effects. Nicotinic effects of CARB are seen in this experiment because nicotinic receptors on sympathetic ganglion cells and adrenal medulla are activated by CARB. This activates these cells to release catecholamines. When its muscarinic effects are blocked by atropine, then the activation of nicotinic receptors on sympathetic ganglia and the adrenal medulla becomes apparent, at least if the release of catecholamines can occur and the alpha receptors are not blocked.

McN is blocked because atropine blocks M1 muscarinic receptors as well as those on vascular endothelial cells.

PILO is blocked because atropine acts as an antagonist at the same receptors on which PILO is an agonist.

VS is blocked because atropine blocks muscarinic receptors in the SA node.

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