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Introduction to Pharmacology > Autonomic Nervous System, Cholinergic Agonists and Antagonists > Flashcards

Autonomic Nervous System, Cholinergic Agonists and Antagonists Flashcards

1
Q

What are the 2 groups of parasympathomimetic drugs?

A
  1. direct-acting agents
  2. cholinesterase inhibitors
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2
Q

What 2 molecules are direct-acting parasympathomimetic agonists? How do they act?

A
  1. choline esters (ACh and numerous synthetic esters)
  2. cholinomimetic alkaloids

act directly on receptors and do not depend upon endogenous ACh for their effects

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3
Q

What are the endogenous agonists at nicotinic and muscarininc cholinergic receptors?

A
  • nicotine
  • muscarine
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4
Q

What is the neurotransmitter released at sympathetic and parasympathetic ganglia?

A

acetylcholine

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5
Q

Effects of direct-acting cholinergic receptor stimulants:

A
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6
Q

What is the prototypical cholinergic agonist? What are 2 reasons it is not used therapeutically?

A

acetylcholine

  1. muscarinic and nicotinic receptors are located at numerous tissues and no selective response can be achieved
  2. duration of action is short, since it is rapidly inactivated by acetylcholinesterases
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7
Q

Target organ effects of acetylcholine:

A
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8
Q

How do the pharmacological and physiological effects of primary choline derivatives/esters compare?

A

PHARMACOLOGICAL: similar to parasympathomimetic effects produced by ACh administration

PHYSIOLOGICAL: not identical and vary in relative selectivity for one organ system to another

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9
Q

There are generally few clinical indications for the use of cholinergic agonists in veterinary medicine, but what 2 are available?

A
  1. Bethanechol - resistant to cholinesterase degradation, promotes bladder contraction in paraplegic dogs/cats, and is used to promote detrusor muscle contraction for detrusor sphincter dyssynergia
  2. Carbachol - topically promotes miosis in ophthalmology, especially after cataract surgery
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10
Q

What are the 3 characteristics of cholinomimetic alkaloids? What 3 are most common in veterinary medicine?

A
  1. plant alkaloids
  2. selective parasympathomimetic agents
  3. evoke effects by direct activation of muscarinic receptors

Pilocarpine, Muscarine, Arecoline

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11
Q

What are the 3 target organ effects of Pilocarpine?

A

(cholinomimetic alkaloid)
1. stimulates flow of secretions, like salivary mucous and gastric/digestive secretions, from exocrine glands
2. contraction of GI smooth muscle contraction by increasing smooth muscle tone and peristaltic activity
3. pupillary constriction

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12
Q

What are the 3 targets organs of Arecoline?

A

(cholinomimetic alkaloid)
1. glands
2. smooth muscles
3. myocardium

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13
Q

How is Pilocarpine typically available as? What are 3 therapeutic uses?

A

(cholinomimetic alkaloid)
1%, 2%, and 4% ophthalmic solutions

  1. miosis and decrease in intraocular pressure in glaucoma
  2. treats keratoconjunctivitis sicca (KCS) in dogs
  3. dilute solutions (0.125%, 0.25%) can be applied directly to the eye to stimulate tear production
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14
Q

What are 2 possible adverse effects of Pilocarpine?

A

(cholinomimetic alkaloid)
1. local irritation of inflammation of the uveal tract
2. repeated use can cause systemic effects - vomiting, diarrhea, and increased salivation

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15
Q

How do cholinesterase inhibitors work? What does this cause?

A

parasympathomimetics that inhibit acetylcholinesterase (AChE)

increases the level of synaptic ACh and enhances the action of ACh at all cholinergic receptors (not just muscarinic, also nicotinic)

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16
Q

What are the 2 groups of cholinesterase inhibitors (indirect parasympathomimetics)?

A
  1. REVERSIBLE: physostigmine, neostigmine, pyridostigmine, edrophonium
  2. IRREVERSIBLE: organophosphates
17
Q

What are the 3 mechanisms that anticholinersterase agents use to prevent the hydrolysis of acetylcholine?

A
  1. reversible AChE inhibition
  2. carbamylation of AChE
  3. phosphorylation of AChE
18
Q

What are the 2 active sites on acetylcholinesterase that recognize acetylcholine? Where do carbamate derivatives act?

A
  1. anionic (negative charge) region where electrostatic binding occurs with the cationic nitrogen of the choline moiety
  2. esteratic site where the carboxyl portion of the acetyl ester binds by covalently

neostigmine and physostigmine interact with the anionic and esteratic sites and are thought to be hydrolyzed in a similar, but slower manner compared to ACh

19
Q

How do physostigmine and neostigmine act in the GI tract, eyes, skeletal muscle, cardiovascular system, and smooth muscle?

A
  • GI: physostigmine and neostigmine cause smooth muscle contraction, increased frequency and strength of peristaltic waves, and acceleration of intestinal content movement
  • EYES: physostigmine causes pupillary constrictions
  • SM: neostigmine stimulates nicotinic receptors and have higher effects at lower doses; large dose can cause twitching
  • CV: no affects of physostigmine and neostigmine at therapeutic doses; high dose can lead to hypotension and bradycardia
    -SM M: smooth muscles of bladder and bronchioles contract
20
Q

What are the 2 principal uses of indirect acetylcholinesterase inhibitors?

A
  1. reverse the effects of nondepolarizing neuromuscular blocking drugs in voluntary muscles
  2. therapy of dogs with myasthenia gravis (MG)
21
Q

What is myasthenia gravis? What can be used as an initial screening test for dogs with suspected myasthenia gravis?

A

congenital absence or acquired autoimmune disease resulting in deficiencies in acetylcholine receptors

Edrophonium

22
Q

What are the 2 most common acetylcholinesterase inhibitors used for myasthenia gravis? Which is preferred? Why?

A

neostigmine, pyridostigmine

pyridostigmine - longer duration and lower adverse GI effects

23
Q

What are the 4 possible adverse effects of acetylcholinesterase inhibitors?

A
  1. increased GI motility
  2. diarrhea
  3. salivation
  4. bradycardia
    (muscarine effects of excess ACh)
24
Q

How do organophosphorus compounds work? What are signs of poisoning?

A

irreversibly phosphorylate the esteratic site of AChE throughout the body —> endogenous ACh is not activated

typical parasympathomimetic actions
- profuse salivation
- vomiting, defecation, urination
- hypermotility in GI tract
- bradycardia
- hypotension
- severe bronchoconstriction
- excess bronchial secretion

25
Q

How do organophosphorus compounds affect skeletal muscles? What causes this? What can happen when it affects the CNS?

A

fasciculations, twitching, muscle paralysis
- persistent excessive stimulation of N receptors

convulsions, death

26
Q

How can organophosphorus compounds be reversed?

A

Pralidoxime (pyridine-2-aldoxime-methiodide) causes an effective removal of the phosphate group from acetylcholinesterase, reactivating it

27
Q

What do muscarinic receptor antagonists (MRA) do? Which is the prototypical agent?

A

block the effects of ACh and related cholinergic receptor agonists from binding to and activating muscarinic receptors
- most are nonspecific for the subtypes (side effects!)

Atropine, an alkaloid from Atropa belladonna

28
Q

Pharmacological effects of Atropine:

A

muscarinic receptor agonist (MRA)
- sympathetic affects

29
Q

What are 3 general effects of muscarinic receptor antagonists? What are they not as efficient in?

A
  1. antispasmodics
  2. decrease/abolish GI hypermotility
  3. decrease hypertonicity of the uterus, urinary bladder, ureter, bile duct, and bronchioles
    - sympathetic!

not as effective as EPI or other adrenergic amines in dilating bronchioles, but atropine is effective in antagonizing excessive cholinergic stimulation

30
Q

What are 3 common uses of Atropine? What is it typically used to counter?

A
  1. treats bradyarrhythmias
  2. facilitates ophthalmoscopic examination of interocular structures (mydriatic and cycloplegic)
  3. treats iridocyclitis due to long duration of action

anti-cholinesterase overdose/toxicity

31
Q

When does excessive salivation and vomiting most commonly occur with Atropine administration? What adverse effect can it have on the eyes? What patients should it be avoided in?

A

topical application of the solution > ointment formulation

  • increased intraocular pressure
  • decrease tear production
  • patients with glaucoma or keratoconjunctivitis sicca
32
Q

What is Glycopyrrolate? How does it compare to Atropine?

A

muscarinic receptor antagonist

  • lower risk of causing tachyarrhythmias
  • penetrates the BBB less effectively
33
Q

What are the 3 effects of Glycopyrrolate?

A

(muscarininc receptor antagonist)
1. decreases volume and acidity of gastric secretions
2. reduces intestinal motility
3. reduces and controls excessive secretions of the respiratory tract

34
Q

What is N-butylscopolamine bromide (NMM)? What is it the preferred treatment of? How does it compare to Atropine?

A

muscarinic receptor antagonist used for the treatment of spasmodic colic in horses

airway obstruction in horses

associated with fewer systemic side effects

35
Q

What are Methantheline, Propantheline, and Methylatropine? How do they compare to other drugs of the same class?

A

muscarinic receptor antagonists

  • do not cross the BBB to an appreciable extent
  • considerably less effective than atropine as antagonists to organophosphates
36
Q

What are 3 common uses of Propantheline?

A
  1. used in dogs with myasthenia gravis that develop significant muscarinic side effects in response to pyridostigmine
  2. SMALL ANIMALS - orally as an antispasmodic/antisecretory agent in the treatment of diarrhea, colitis, and acute irritable bowel syndrome
  3. HORSES - administered IV to reduce colonic peristalsis and relax the rectum fo easy rectal examination and surgery

Introduction to Pharmacology (39 decks)

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