GI Endocrinology

Question 1

What’s the role of secretin?

Answer 1

• release is stimulated by H+ in the duodenum
• leads to secretion of bicarbonate-containing fluids and bile from the pancreas, and biliary epithelium, respectively

Question 2

What’s the role of glucagon?

Answer 2

It’s secreted by the pancreatic alpha cells –> actions opposite of insulin
- promotes glycogenolysis and gluconeogenesis

Question 3

What’s the role of glucagon-like-peptide (GIL) and gastric-inhibitory peptide (GIP)?

Answer 3

• They are from the same gene product as glucagon, but is made from L cells in the GI
• they are known as incretins
• their action = enhance nutrient-induced insulin secretion
• GLP-1 = most potent incretin
• also modulate intestinal glucose absorption by inhibition of gastric motility and GLP-2 mediated up-regulation of glucose transporters

Question 4

What’s the role of gastrin?

Answer 4

• it’s produced by G cells in the gastric antrum and duodenum
• stimulated by gastric distension, inhibited by low gastric pH (<3)
• primary action = acid secretion
• works with acetylcholine from the PNS and histamine to regulate H+ secretion
• trophic effects on gastric epithelium: increased blood flow, pepsinogen release, and antral motility
• trophic effects on pancreatic and duodenal tissues, too
• also influences pancreatic enzyme production

Question 5

What’s the role of cholecystokini (CCK)?

Answer 5

• regulates overall digestive function
• stimulated by H+, free fatty acids, and amino acids in the duodenum
• secreted by I cells in the duodenum and jejunum
• also works as a neurotransmitter in the enteric nervous system
• stimulates gallbladder contraction and pancreatic enzyme secretion
• relaxes sphincter of Oddi, and slow gastric emptying
• stimulates pancreatic growth

Question 6

What’s the role of somatostatin?

Answer 6

• synthesized in the hypothalamus, pancreatic delta cells, GI D cells and subsets of neurons in CNS and enteric nervous system
• secretion is stimulated by fat and protein in the duodenum, as well as gastric acid
• mainly inhibitory effects –> slows down gastric emptying, decrease pepsinogen, decrease insulin, decrease gallbladder contraction, decrease GI motility, and decrease nutrition absorption

Question 7

What’s the role of motilin?

Answer 7

• secreted by GI cells
• cyclic secretion, depending if fed or fasted state
• stimulated by fat and H+ in the small intestines –> coordinates gastric, pancreatic, and gallbladder secretion
• in fasted state, helps to initiate and migrating motility complexes (MMC) = main function

Question 8

What’s the role of ghrelin?

Answer 8

• similar in structure as motilin
• secreted by the stomach
• stimulates growth hormone secretion by the pituitary, appetite, and adipocyte growth
• it’s the link between dietary nutrients, caloric energy, and pituitary-GH axis required for growth regulation

Question 9

What’s the role of serotonin?

Answer 9

serotonin = 5HT
- it’s a neuropeptide and hormone
- found in enteric neurons and enterochromaffin cells
- secreted in the intestines
- promotes smooth muscle contractions and motility

Question 10

What’s the typical signalment for gastrinoma?

Answer 10

Dogs: around 8yo
Cats: slightly older
<50 cases reported in vet med

Question 11

What are the typical presenting complaints for gastrinoma?

Answer 11

• vomiting, diarrhea, and weight loss
• vomiting = gastric antral hyperplasia, ulceration
• can have reflux esophagitis –> regurgitation, esophageal colic
• if very hypertrophic, can have a outflow obstruction
• gastrin inhibits water resorption in the intestines –> diarrhea
• none specific signs on PE

Question 12

What changes are noted on blood work for gastrinoma?

Answer 12

None specific, more relating to the consequence of hypergastrinemia, such as inflammation, gastric ulcer, vomiting, diarrhea, or other concurrent illness

Question 13

How can imaging help with diagnosis of gastrinoma?

Answer 13

AUS better than plain radiographs
- endoscopy can assess esophagitis, and get samples, but unlikely to provide definitive diagnosis for gastrinoma

Question 14

What are some differentials for hypergastrinemia?

Answer 14

• kidney disease
• liver disease
• other GI disease
• drugs that decrease acid production

Question 15

What provocative testing can be done for gastrinoma?

Answer 15

• secretin or calcium
• neither leads to increased gastrin release in healthy individuals but both can increase gastrin release from gastrinoma
• secretin testing –> not all dogs with gastrinoma will have a >2x increase of gastrin compared to baseline
• Calcium = preferred, but watch for arrythmia

Question 16

Where is the most common location for gastrinoma?

Answer 16

R limb or body of the pancreas
metastasis = common (85%), LN, mesentery, liver, spleen

Question 17

What dermatological issues can be noted with glucagonoma?

Answer 17

Necrotizing migratory erythema
(but is more commonly seen in liver disease)

Question 18

What’s the signalment for glucagonoma?

Answer 18

• mid age to older dogs. the one reported cat was 6yo
• lethargy, decreased appetite
• skin ulcerations/ erosions

Question 19

What lab work abnormalities are noted with glucagonoma?

Answer 19

non-specific
- increase in ALP, ALT
- decrease in albumin, cholesterol, and BUN
- similar to liver dysfunction, and it would be the more common cause of NME
- liver function testing (ex. bile acids) = normal in dogs with glucagonoma

Question 20

What’s the role of diagnostic imaging?

Answer 20

• AUS is more useful than rads but tumour is not often identified
• non-specific changes can be noted with the liver
• CT may be better at detecting a pancreatic mass

Question 21

How is glucagonoma diagnosed?

Answer 21

• definitive diagnosis require demonstration of elevation glucagon in the blood
• no commercially available assay for dogs or cats
• can try testing for amino acid (ex. arginine, histidine and lysine) –> hyperglucagonemia stimulate hepatic gluconeogenesis and accelerates amino acid turnover, so may have lower values in the blood

Question 22

Where is glucagonoma usually found?

Answer 22

• anywhere in the pancreas
• metastasis = common –> liver, LN
• metastatic site can be functional

Question 23

What’s carcinoid?

Answer 23

carcinoid = neuroendocrine tumours that secrete vasoactive substance such as 5-HT (serotonin) or kinins
- rare in dogs and cats
- in vet med is more of a space occupying mass
- metastasis in common (ie non functional)
- in people, can have carcinoid syndrome –> watery diarrhea, abdominal discomfort, abdominal cramps, bronchoconstriction and facial flushing
- Tx = Sx
- diagnosis via histology

Question 24

What’s pancreatic peptidoma?

Answer 24

A pancreatic tumour that stains positive for pancreatic peptide
- rare in the dog
- mostly nonfunctional
- signs associated with excessive PP = minimal
- chronic vomiting, duodenal ulcers, hypertrophic gastritis