PNS

Question 1

What are the PNS affects on the body? Think rest and digest

Answer 1

Stimulates flow of saliva
slows heartbeat - decreased CO
constricts bronchi
stimulates peristalsis and secretion
stimulates release of bile
contracts bladder
mitosis (constriction of pupil)

Question 2

Atropine - when might you use it?

Answer 2

Methiocarb toxicity - dose conservatively - too high a dose will stop GIT and prolong time of ingested toxins

Question 3

Parasympathetic outflow
look at picture

Sympathetic Outflow

Answer 3

PSN = nicotinic (ACh) muscarinic

SNS = nicotinic (ACh) + Adrenergic (alpha, beta)

There is ACh in both PNS and SNS therefore excessive ACh will cause overstimulation of PNS but also the somatic nervous system

Question 4

Parasympathetic outflow
look at picture

Sympathetic Outflow

Answer 4

PSN = nicotinic (ACh) muscarinic

SNS = nicotinic (ACh) + Adrenergic (alpha, beta)

There is ACh in both PNS and SNS therefore excessive ACh will cause overstimulation of PNS but also the somatic nervous system

Question 5

Parasympathomimetics (think mimics the PNS system)

ophthalmic - pilocarpine
urinary - bethanecol
GIT - cisapride

note we can’t use ACh as a drug because it is rapidly broken down

Answer 5

OPTHALMIC
pilocarpine: muscarinic agonist
causes miosis (constriction)
Use pilocarpine eye drops for glaucoma to decrease the IOP by opening up the drainage channel. If there is glaucoma present (increased IOP) don’t give atropine because this will crush the the drainage channel.

URINARY
bethanecol: muscarine against
assists in urination, urethea (must not be blocked)

GIT
cisapride: stimulates ACh release from the myenteric plexus
increases GIT motility, used in ileus

Note re the eye:
when an animal presents with an inflammedeye/conjunctivitis/miosis (constriction), give atrapine to causes dilation (mydraisis) which will take away the pain. But need to make sure glaucoma is not present, check intraoculuar pressure using tachnometer. If glaucoma is present give pilocarpine.

Glaucoma - inflamamtion (causes pain and spasm in the eye), crushes the retina, causes irreversible damage so if you see a red angry eye always take IOP, because if you give atropine it will releive the pain but you will crush the draingae channel and accelerate the pathway to blindness

Question 6

The effects of excessive ACh discharge can be predicted

Answer 6

Muscarinic signs

• salivation
• lacrimination
• diarrhoea
• emesis (vomiting)
• miosis (pupil constriction)
• bradycardia

Somatic signs
- muscle tremors

CNS signs
seizures

Question 7

Parasympatholytics - (think lytic so the drugs will decrease PNS activity)

Atropine
glycopyrolate
propantheline

Answer 7

ATROPINE
used in CVS and ophthalmic
Contraindicated for glaucoma.
Atropine will cause mydriasis for 1-3 days so better to use tropicamide which has a DOA of 4-6 hrs.

GLYCOPYROLATE used for CVS effects
-very similar to atropine except longer DOA, less lipophilic, so crosses the BBB less. SO lead CNS side effects

PROPANTHELINE
used for UGT - decreases GIT contraction or decreases spasm. i.e use for equine rectal exam

Question 8

MOA

Answer 8

competitive antagonism of ACh at muscarinic system