Endocrinology of Horses (PPID and EMS)

Question 1

Pathophysiology of PPID

Answer 1

Hypertrophy/hyperplasia of Pars intermedia (neoplasia) → Loss of dopaminergic control (oxidative stress and ↓ dopamine secretion and loss in inhibition) → Excess proopiolipomelanocortin (POMC, no neg feedback control) → ↑ ACTH and hyperadrenocorticism

Question 2

What products are produced from Pars intermedia dysfunction

Answer 2

↑ cortisol
MSH and ↑ androgen from adrenal cortex: Hirtuism
ACTH and ↓ ADH: PU/PD
Compression of Pars nervosa: seizures
B-endorphins: lethargy

Question 3

CS associated with ↑ cortisol?

Answer 3

Vasoconstriction
Protein depletion in dermis
Protein catabolism
Immunosuppression
IR (laminitis)

Question 4

Resting plasma ACTH or a MSH (test for PPID)

Answer 4

Collect blood in EDTA tube
Resting ACTH >35 pg/ ml (not cortisol)

Question 5

TRH stimulation test (test for PPID)*

Answer 5

Most sensitive for early cases
Corticotrophs abnormally stimulated by TRH (give IV)
If @ baseline >36 pg/ ml, >110 pg/mL @ 10 min (measures ACTH response)

Question 6

Drugs for tx PPID

Answer 6

Pergolide mesylate
Capergoline
Cyproheptadine

Question 7

Pergolide mesylate

Answer 7

Doperminergic agonist → compensates for less dopaminergic neurons and slows progression

Question 8

Capergoline

Answer 8

Long-acting dopamine receptor agonist

Question 9

Cyprohepatadine

Answer 9

Inhibits action of excitatory NT serotonin

Question 10

Equine metabolic syndrome (EMS)

Answer 10

A cluster of risk factors that indicate that a horse is greater risk of developing endocrine laminitis

Question 11

Pathophysiology of EMS

Answer 11

↓ in tissue response to circulating insulin which impairs insulin-mediated glucose → more insulin secreted from pancreas to compensate for lower tissue response → hyperinsulinemia → laminitis

Question 12

Resting serum insulin (test for EMS)

Answer 12

Blood collected after short fasting period
Insulin > 20 uU/ mL, baseline elevated
False negs, poor sensitivity

Question 13

Oral sugar test/ OST (test for EMS)

Answer 13

More sensitive
Syrup given → 60-90 min to collect blood → place in a red top/ purple top tube

Question 14

Leptin baseline (test for EMS)

Answer 14

Hormone produced by adipocytes
↑ in EMS horses

Question 15

EMS management

Answer 15

Limit calorie intake, eliminate pasture access and ↑ exercise
Forage with non-structural carbs <10% with soaking and balancer feeds
Avoid treats and high fat feeds
No exercise with laminitis

Question 16

Drugs for EMS

Answer 16

Metformin
Levothyroxine
Velagliflorzin

Question 17

Metformin

Answer 17

Horses with severe ID in combo with management changes
Direct effect on the enterocyte and decreases enteric glucose absorption and consequently the insulin response to an OGT in horses

Question 18

Levothyroxine

Answer 18

With ↑adiposity to accelerate weight loss through ↑ metabolic rate

Question 19

Velagliflorzin

Answer 19

Na-glucose linked transport-2 inhibitor
Reduces glucose resorption and promoting excretion