3rd lecture - parasympatholytics

Question 1

another 2 terms for parasympatholytics

Answer 1

Anticholinergic agents
Cholinoblockers

Question 2

parasympatholytics are broadly divided into (2)

Answer 2

1) Antimuscarinic agents
2) Antinicotinic agents

this division is not rigid

Question 3

Skeletal muscle relaxants (neuromuscular blocking agents) are typically what type of drug

Answer 3

Antinicotinic agents.

Question 4

Parasympatholytic drugs prevent

Answer 4

ACh from producing its characteristic effects in structures innervated by postganglionic parasympathetic nerves and prevent ACh effects on smooth muscle cells.

Question 5

Typical natural representatives of Antimuscarinic agents are

Answer 5

alkaloids of plants belonging to the Solanaceae family such as:

Deadly nightshade (Atropa belladonna)((source of Atropine))

Jimsonweed (Datura stramonium)((source of Atropine))

Black henbane (Hyoscyamus niger) - scopolamine

Question 6

duration of the effect of atropine is

Answer 6

long, particularly in the event of a topical route of administration (2-3 days in the eye).

Question 7

Pharmacokinetics of atropine

Answer 7

Atropine absorbs well in case of all routes of administration and is evenly distributed in the organism.

Hydrolysis occurs slowly due to the effect of carboxylesterase.

Question 8

classic example of a parasympatholytic

Answer 8

atropine

Question 9

atropine Mechanism of action

Answer 9

blockade of postsynaptic receptors in competition with acetylcholine.

Atropine binds the receptor active centre and the mediator will be unable to access the receptor.

The blockade will be temporary and the effect will pass when the substance is eliminated.

Question 10

Cholinesterase inchibitors eliminate the effect of atropine by

Answer 10

inducing the accumulation of acetylcholine at nerve endings which makes it able to compete with atropine.

Other cholinomimetics have no effect.

Question 11

Although cholinoblockers act on all postganglionic cholinergic nerve endings, this block is not

Answer 11

equally effective throughout the body.

Salivary and chlolinergic sweat glands are susceptible.

GI and urinary tract smooth muscle less sensitive.

Difficult to achieve a selective action on targeted structures without concurrently inducing side effects on other sites.

Question 12

atropine effect on the GI tract

Answer 12

Inhibitory effect of atropine on secretion already at low doses. It inhibits the function of lacrimal, sweat, salivary, bronchial and intestinal glands.

Atropine causes relaxation of GI smooth muscle by inhibiting contractile effects of cholinergic nerve impulses.

Helpful in treatment of intestinal spasm and hypermotility.

Question 13

effect of atropine on bronchioles

Answer 13

Atropine decreases secretion and increases luminal diameter of the bronchioles.

especially valuable in counteracting constriction of bronchioles following overdosage of parasympathomimetic drug.

Question 14

effects of atropine on the Cardiovascular system

Answer 14

Does not technically directly impact blood pressure, is a positive inotrope as atropine eliminates the vagus nerve’s depressing effect on the heart resulting in tachycardia. ‘

Large doses of atropine are actually directly depressant to the myocardium and also causes cutaneous dilation as a result of a direct vascular smooth muscle effect.

Question 15

The basis of the effect of mydriasis by atropine

Answer 15

is the paralysis of the ciliary muscle of the eye lens and sphincter pupillae muscle, the pupil dilates and does not react to light. This is accompanied by an increase in internal eye pressure.

Effect lasts in the eye for days.

Question 16

effect of atropine on the CNS

Answer 16

Atropine does not cause central nervous system side effects in therapeutic doses;

humans experience hallucinations in large doses, animals in large doses experience mania, irritable behaviour, increase in motor activity until coma.

Question 17

What is scopolamine?

Answer 17

is a natural or synthetically produced tropane alkaloid and anticholinergic drug that is used as a medication to treat motion sickness and postoperative nausea and vomiting. It is also sometimes used before surgery to decrease saliva.

Question 18

Large doses of scopolamine cause

Answer 18

delirium in horses, dogs and cats, small doses cause mainly depression.

Question 19

Antidote to atropine/parasympatholytics

Answer 19

Indirect-acting cholinomimetics
aka Cholinesterase inchibitors

Question 20

Clinical uses of parasympatholytics such as atropine

Answer 20

Inhibition of the function of intestinal glands, antispasmodic medicine in the case of spasms of the intestinal tract,

uterus, urinary bladder or bronchial spasms.

Premedication before general anaesthesia, in order to reduce the secretion of glands, in order to strengthen heart function (to prevent or treat bradycardia).

Question 21

Glycopyrrolate clinical uses

Answer 21

increases pressure by reducing parasympathetic tone

Tachycardia response lower.

In dogs diminishes the volume and acidity of gastric secretions, reduces intestinal motility, reduces secretions of the respiratory tract.

Its duration of action exceeds that of atropine.

Question 22

N-butylscopolamine bromide is a

Answer 22

Anticolinergic, similar in action to atropine.
Spasmolytic.

Used in case of GI spasms in horses. Investigations confirm efficacy also in case of bronchoconstriction (acts as bronchodilator).

Question 23

Propantheline Is used as a

Answer 23

smooth muscle relaxant. Also acts as an autonomic ganglionic blocker (n-colinoblocking effect). Propantheline bromide is an antimuscarinic agent.

Most likely it contributes to the antispasmodic effect on GI smooth muscle.

Question 24

Antinicotinic agents are

Answer 24

(neuromuscular blocking agents)
Peripheral muscle relaxants

Substances that block the impulse transmission from the motor nerve ending to the striated muscle. Curare-like substances.

Question 25

Antinicotinic agents (neuromuscular blocking agents) / curare-like substances cause muscle paralysis in the following order:

Answer 25

Extraocular and face muscles
Muscles of the neck and tongue
Limb muscles
Trunk
Intercostal muscles, diaphragm.

Cause of death is respiratory paralysis, the animal will remain fully conscious until the end.

Question 26

Mechanism of action of nondepolarizing muscle relaxants.

Answer 26

effects inhibit the nerve-muscle transmission, compete with acetylcholine, inhibit acetylcholine-induced membrane depolarization.

Indirect-acting cholinomimetics can be used to increase the amount of acetylcholine in postsynapse, impulse transmission will be restored (antidotes).

Question 27

Substances with depolarizing effect induce

Answer 27

membrane depolarization by themselves similar to acetylcholine and compete with acetylcholine. Paralysis is preceded by muscle fibre contraction induced by depolarization.

There is no antidote in case of depolarizing substances.

Question 28

In case of nondepolarizing substances the antidote is

Answer 28

cholinesterase inhibitors. This is also referred to as decurarization.