VPT 321: Veterinary Neuropharmacology (2+1) copy 1

PHARMACOLOGICAL ACTIONS

Skeletal muscles

On i.v administration of  non depolarizing blocker rapidly produces muscle weakness followed by flaccid muscle paralysis.

• The order of paralysis is as follows: fingers,extraocular,hands,feet,arm,leg,neck,face,trunk,intercostal muscles,diaphragm and respiration stops.
• Recovery occurs in reverse fashion. The peak effect and duration of action depends on several factors like anaesthetic used, haemodynamic status, renal and hepatic status etc.,
• Depolarizing agents produce fasciculations lasting few seconds before inducing flaccid paralysis.
• Apnoea occurs withing 45-90 seconds but lasts 2-5 minutes recovery is rapid.
• d-tubocurarine has maximum effect.

Autonomic ganglia

• Cholinergic receptors in autonomic ganglia is nicotinic, competitive blockers produce some degree of ganglionic blockade.
• Succinylcholine cause ganglionic stimultion by its agonistic action on nicotinic receptors.

CVS

• d-tubocurarine produce significant fall in blood prssure - due to ganglionic blockade, histamine release and reduced venous return.
• Gallamine has muscarinic vagal blocking action in the heart and cause tachycardia.
• Pancuronium and Vencuronium cause tachycardia with negilible effect on BP and heart rate.
• Sucinylcholine has variable effect.
• Generally bradycardia due to activation of vagal ganglia followed by tachycardia and rise in BP due to stimulation of sympathetic ganglia.

GIT

• Competitive blockers may enhance post operative paralytic ileus after opeation.

CNS

• Being a quaternary compound do not cross blood brain barrier.