Chapter 118 - Motility Disorders

Question 1

Discuss about causes of acquired megaesophagus in dogs?

Answer 1

1. idiopathic: most adult onset
2. myasthenia gravis: account for the majority of cases with a known cause
3. hypoadrenocorticism
4. lead and thallium poisoning
5. lupus
6. esophageal neoplasia
7. severe esophagitis
8. inflammatory myopathies
9. immune mediated polymyositis
10. infectious and preneoplastic myositis
11. dermatomyositis
12. peripheral neuropathies
13. lar par
14. myasthenia gravis
15. esophagitis
16. chronic or recurrnet gastric dilatation with or without volvulus
17. hypothyroidism (no clear link)

Question 2

What are the consequences of small intestinal transit disorders?

Answer 2

Bacterial overgrowth, endotoxemia and septicemia

Question 3

What is underlying cause in megacolon in cats?

Answer 3

Idiopathic, suspect generalized dysfunction of colonic smooth muscle

Question 4

What is the treatment option if megacolon is refractory to medical therapy?

Answer 4

subtotal colectomy with preservation of ileocolin junction, carries generally favorable prognosis, complication is mild to moderate diarrhea may persist for weeks to months.

Question 5

What’s the percentage of body’s serotonin located in GI tract?

Answer 5

Above 95%, and more than 90% of that stores is in the enterochromaffin cells that are scattered in enteric epithelium from the stomach to colon. Remaining serotonin is store in ENS, where 5-HT acts as a neurotransmitter

Question 6

What are 3 subtypes of 5-HT (5-hydroxytryptamine, serotonin) and drugs used for each receptors?

Answer 6

(1) 5-HT1p receptor, no drugs developed
(2) 5-HT3 receptor, 5-HT3 receptor antagonist: ondansetron and granisetron, to treat nausea and vomiting seen with chemotherapy
(3) 5-HT4 receptor, 5-HT4 agonist: cisapride (enhance neurotransmission, and depend on natural stimuli to evoke peristaltic and secretory reflexes)

Question 7

Discuss differences between Cisapirde and metoclopramide’s MOA

Answer 7

(1) Cisapride does not cross BBB
(2) Cisapride does not have antidopaminergic effects: does not have anti-emetic action, does not cause the extrapyramidal effects
(3) Cisapride has more potent and broader prokinetic activity than metoclopramide
A. Cisaprdie: increasing motility of colon, esophagus, stomach, and SI
B. Metoclopramide: gastric antrum, proximal duodenum

Question 8

What is one of lethal complication of Cisapride noted in human?

Answer 8

arrhythmia and death, associated with concomittant administration of other drugs that inhibit cisapride’s metabolism

Question 9

What is MOA of metoclopramide?

Answer 9

1. central dopaminergic antagonist
2. periphral 5-HT3 receptor antagonist
3. 5-HT4 receptor agonist with GI and CNS effects

Question 10

True or false: metoclopramide has little or no effect in colonic motility, NOT useful in megacolon

Answer 10

True

Question 11

What is extrapyramidal effects? What can be used to reverse it?

Answer 11

extrapyramidal effects: dopamine antagonism in striatum cause adverse effects

1. involuntary muscle spasm
2. motor restlessness
3. inappropriate aggression
4. frenzied dog and cats
5. Reverse: restoring an appropriate dopamine to ACH balance with the anticholinergic action of diphenhydramine 1.0 mg/kg IV

Question 12

True or false: Erythromycin can accelerate colonic transit in cats, not in dogs.

Answer 12

False: accelerate colonic transit in dogs and stimulate canine but not feline colonic smooth muscle in vitro