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Can you name some examples of choline esters?
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- Acetylcholine
- Methacoline (acetyl-beta-methylcholine) - Carbachol (carbamoylcholine) - Bethanechol (carbamoyl-beta-methylcholine) (S)- is much more potent than (R)- at muscarinic receptors |
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Are choline esters distributed well to the CNS? Why/Why not?
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No because they are hydrophilic
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Name some cholinomimetic Alkaloids
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1. Pilocarpine
2. Muscarine 1 & 2 are mainly muscarinic 3. Nicotine 4. Lobeline 3 & 4 are mainly nicotinic |
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M1 Receptor:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. Nerves
2. G_q/11 3. IP3, DAG cascade |
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M2 Receptor:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. Heart, Nerves, Smooth Muscle
2. G_i/o 3. Inhibition of cAMP production, activation of K+ channels |
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M3 Receptor:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. Glands, Smooth Muscle, Endothelium
2. G_q/11 3. IP3, DAG cascade |
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M4 Receptor:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. CNS
2. G_i/o 3. Inhibition of cAMP production |
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M5 Receptor:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. CNS
2. G_q/11 3. IP3, DAG cascade |
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Nictotinic Receptor of the muscle type:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. Skeletal muscle neuromuscular junction
2. pentamer [(alpha1)2_beta1_delta_ gamma] 3. Na+, K+ depolarizing ion channel |
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Nicotinic Receptor of the neuronal type:
1. Where is it found? 2. What subtype of G protein is involved? 3. What is the post-receptor mechanism that is involved? |
1. CNS postganglionic cell body, dendrites
2. pentamer with alpha and beta subunits only 3. Na+, K+ depolarizing ion channel |
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A 61 year-old man is noted to have increased intraocular pressure on a routine eye examination. The visual acuity is normal in both eyes. The dilated eye examination reveals no evidence of optic nerve damage. Visual field testing shows mild loss of peripheral vision. He is diagnosed with primary open angle glaucoma and is started on pilocarpine opthalmic drops.
1. How would you classify pilocarpine as a drug? 2. What is the action of pilocarpine on the muscles of the iris and cilia? |
1. It is an alkaloid that is a cholinoceptor agonist
2. Constriction of these muscles |
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A 62 year-old woman is noted to have open angle glaucoma. She inadvertently applies excessive pilocarpine to her eyes. This may result in which of the following?
A. Bronchial smooth muscle dilation B. Decreased GI motility C. Dilation of blood vessels D. Mydriasis |
C. Dilation of blood vesselsM
Excessive pilocarpine may initially result in dilation of blood vessels with a drop in blood pressure and a compensatory reflex stimulation of heart rate. Higher levels will directly inhibit heart rate. In addition, pilocarpine stimulation of muscarinic cholinoreceptors can result in miosis, bronchial smooth muscle constriction, and increased GI motility. |
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Muscarinic cholinergic agonists
A. Activate inhibitory G proteins (G_i) B. Decrease production of IP3 C. Decrease release of intracellular calcium D. Inhibit the activity of phospholipase C |
A. Activate inhibitory G proteins (G_i)
In addition to activating inhibitory G proteins, muscarinic cholinergic agonists stimulate the activity of phospholipase C, increase production of IP3, and increase release of intracellular calcium. |
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Choline esters like carbachol are most likely to cause which of the following adverse effects?
A. Anhydrosis (dry skin) B. Delirium C. Salivation D. Tachycardia (rapid heart rate) |
C. Diarrhea, salivation, and lacrimation may be seen.
Heart rate is usually slowed, and choline esters do not cross the blood brain barrier so delirium is not an adverse effect. |
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Which of the following cardiac effects may be caused by the action of cholinergic agonists or by the action of acetylcholine?
A. Increased atrioventricular (AV) conduction velocity B. Stimulation of the sinoatrial node (SA node) C. Negative inotropic effect D. Decreased atrioventricular (AV) conduction velocity E. Increased production of ectopic foci |
C. Negative inotropic effect
Acetylcholine is the neurotransmitter released from cholinergic or parasympathetic (vagal) nerve fibers at the heart. Cholinergic agonists such as choline esters and anticholinesterases act as parasympathomimetics at the heart to simulate acetylcholine's action and decrease the force of myocardial contraction (negative inotropism). Increased conduction velocity (or decreased atrioventricular conduction time), as well as increased electrical activity throughout the heart, and at the SA node in particular, are typical cardiac responses resulting from adrenergic stimulation or cholinergic blockade. |
