Equine Endocrine Flashcards
(46 cards)
1
Q
Picture of Equine Metabolic Syndrome
A
- Overweight
- “Easy keeper”
- History of laminitis
- Regional adiposity
- Especially “cresty” neck
- Resting insulin and glucose levels: insulin is elevated and glucose is high
- Oral glucose absorption test was positive
2
Q
Treating EMD
A
- Diet and exercise
- Can also use levothyroxine and metformin
3
Q
Biologically active thyroid hormones
A
- 2 biologically active hormones: thyroxine (T4) and 3,5,3-triiodothyronine (T3)
- Plus reverse triiodothyronine rT3
4
Q
What controls T4, T3, and Reverse T3?
A
- Thyroid stimulating hormone or TSH
- Work via feedback system to keep metabolism in homeostasis
5
Q
T3 and T4 metabolic effects
A
- Increase concentrations of ATP
- Increase metabolism
- Increase HR
- Increase GI motility
- Increase sensitivity to catecholamines and increases sympathetic tone
6
Q
Site of release of thyroid releasing hormone
A
- Hypothalamus
7
Q
Action of TRH
A
- causes release of Thyroid stimulating hormone TSH
8
Q
Things that cause negative feedback for TRH
A
- T3, T4
9
Q
TSH site of release
A
- Anterior pituitary lobe
10
Q
Action of TSH
A
- Causes release of T3 and T4
11
Q
Levothyroxine (for horses)
A
- Manufactured form of T4
- Used typically to treat hypothyroidism in other species, but it’s very rare in horses
12
Q
Mechanism of action of Levothyroxine
A
- Synthetic form of thyroxine
- Converted to T3
- T3 and T4 bind to thyroid receptor proteins in the cell nucleus
13
Q
What causes the metabolic effects of levothyroxine?
A
- Metabolic effects caused by control of DNA transcription and protein synthesis
14
Q
Effect of Levothyroxine for EMS horses
A
- Accelerates weight loss with horses on a controlled diet (NEED TO BE ON A CONTROLLED DIET TOO)
- Increases metabolic rate
- Increases insulin sensitivity
15
Q
Dosing of Levothyroxine
A
- Usually once a day dosing
- Mild state of hyperthyroidism induced
16
Q
How long should EMS horses be on levothyroxine?
A
- 3-6 months only
- Then slowly weaned off
17
Q
Side effects of levothyroxine
A
- Not described at listed doses
18
Q
Metformin use
A
- Used in human diabetes mellitus type II
- Decreases amount of glucose produced by liver (gluconeogenesis) and reduces glucose absorption from the intestine
19
Q
Metformin in horses
A
- Controversial due to absorption and bioavailability
- No real change of glucose absorption in some studies depending on dose
- Decreased intestinal absorption of glucose and limits post prandial insulin concentrations
- Used for EMS to help decrease weight
20
Q
Dosing frequency and dose timing of metformin
A
- Give 30-60 minutes prior to feeding
- 2-3 times a day
21
Q
Monitoring for Metformin
A
- Check insulin concentrations 2 hrs post-feeding before and 7 days after initiating metformin
- Doesn’t always work
22
Q
Problems with metformin
A
- Expensive: $2000 a year!
- No long term studies in horse
- No FDA approval
23
Q
Side effects of metformin (people only)
A
- Lactic acidosis - rhabdomyolysis
- GI pain
- Interferes with thyroid medication
24
Q
Sodium Glucose Co- transporter 2 (SGLT2) Inhibitor Use in humans
A
- FDA approved in humans for use with diet and exercise to lower blood glucose in adults with diabetes mellitus Type 2
- SGLT2 inhibitors lower blood glucose by causing diuresis through the kidneys
25
SGLT2 effect in horses
- Glucose loss through kidneys
- Weight decrease
- Blood pressure decrease
- Used for EMS in conjunction with diet changes
26
Side effects of SGLT2 in humans
- Ketoacidosis
| - Mild genital infections
27
Canagliflozin and Velagliflozin
- Experimentally used in horses with EMS
| - Decreased insulin concentrations
28
Canagliflozin and velagliflozin adverse effects
- None reported so far, but more research should be done
29
Drugs used to aid EMS therapy
- Levothyroxine
- Metformin
- SGLT2 inhibitor
- Canagliflozin and Velagliflozin
30
PPID characteristics
- mild nasal discharge
- Hair coat still long and patchy
- Digital pulses within normal limits and TPR WNL
31
Pituitary Pars Intermedia Dysfunction Overview
- Dysfunction of the intermediate lobe of the pituitary causes the disease
- Typically in horses <14 years of age
- Problem is lack of dopamine
32
PPID Dopamine
- Dopamine normally decreases/regulates hormones release from the intermediate lobe of the pituitary
- If not enough dopamine, hormones released without check and balance
33
Hormones that get out of whack in PPID due to lack of dopamine
- Proopiomelanicortin --> ACTH --> ACTH, alphaMSH, Corticotropin-like intermediate peptide (CLIP), endorphins
34
Diagnosis of PPID
- Endogenous ACTH concentrations
| - Thyrotropin releasing hormone stimulation test
35
Endogenous ACTH
- works well in horses with clinical PPID
- Not always accurate in early stages
- ACTH and Cortisol are pulsatile all day
- Also increase in late summer/fall inreparation for winter
36
Thyrotropin Releasing Hormone Stimulation Test
- TRH causes intermediate lobe of the pituitary to increase production of ACTH
- Especially useful in horses in the early stage of disease
- PPID horses will have a major increase
- If you get an increase greater than 100-110 then it definitely has PPID
37
Primary treatment for PPID
- Prascend (AKA Pergolide)
38
Prascend MOA
- Synthetic ergot derivative
- Long acting dopamine receptor agonist
- Doesn't affect norepinephrine, epinephrine, or serotonin pathways
- Inhibits release of prolactin
- Stimulates dopamine receptors
- Inhibits production of POMC, ACTH, MSH
39
Prascend precautions
- Use caution in breeding animals
- pregnant or lactating mares
- May interfere with reproductive functions
40
Side effects of Prascend
- Sweating
- Inappetence
- Transient anorexia
- Lethargy
- Mild CNS signs (possible, not often)
- Colic
- Diarrhea
41
Monitoring for Prascend
- Recheck ACTH concentrations in 4-6 weeks
- Much depends upon improvement of clinical signs
- If improvement, don't increase dose
- If no improvement, increase dose
42
Cyproheptadine Indication
- Use for horses with PPID
43
Cyproheptadine MOA
- Serotonin (5-HT) receptor block agent
- Serotonin stimulates intermediate lobe of the pituitary
- Exactly why it works is unclear
- Serotonin not primary stimulator of PID
44
Cyproheptadine Use
- Used with pergolide to help with clinical signs of PPID
| - Typically used when you reach a maximum dose for Prascend
45
Route for cyproheptadine
- Oral medication
46
Side effects of cyproheptadine
- sedation
- Dry mucous membranes
- Tachycardia
