Canine Growth Hormone Disorders Flashcards
What’s another source of growth hormone in the dog?
From mammary gland, induced by progestins
- no a pulsatile secretion, not influenced by GHRH, not affected by somatostatins
- the gene is identical to the pituitary one
Is the growth hormone release controlled in the dog?
- GH is secreted from the anterior pituitary
- the release is stimulated by GHRH
- negative feedback via IGF-1 & GH itselfW
- inhibited by somatostatin
- the release in pulsatile (controlled by GHRH), the in between GH is controlled by somatostatin
- Ghrelin (released from the stomach), can also stimulate GH released via non-GHRH receptors. Ghrelin is more potent than GH in young dogs
When is mammary GH normal in dogs?
in dogs in diestrus
What’s the physiological effects of GH in dogs?
- it has both (rapid) catabolic (via insulin antagonism) and (slow) anabolic effects (via IGF-1)
- the diabetogenic effects: increased lipolysis, gluconeogenesis, restricted glucose transport across cell membranes, hyperglycemia
- IGF-1 is protein bound so has long-lasting effect on the body
- IGF-1 inhibits further secretion of GH directly, and indirectly via stimulation of somatostatin release
What’s the pathogenesis of acromegaly in dogs?
- bony and soft tissue growth
- insulin resistance
- all due to chronic excessive GH release
- it can be from mammary tissues (progesterone stimulation)
- can also be due to hypothyroidism
- pituitary somatotroph adenoma = rare
What are some clinical manifestations of canine acromegaly?
- over growth/ swelling of soft tissues in head, neck, abdomen
- snoring, dyspnea
- arthropathy from cartilage overgrowth, neck stiffness
- organomegaly
- polyuria, but not necessarily due to glucosuria. Diabetes mellitus can occur
- thick skin folds, esp in the neck
- hyperglycemia
- increased ALP
- German Shepherds
How is acromegaly diagnosed in dogs?
- GH suppression test (with somatostatin administrations) - fails to suppress
- GH stimulation test (with GHRH administration) - fails to stimulate
- GH assay
- IGF-1
- if there is no progesterone use for a dog with increased GH, should test for hypothyroidism
How is canine acromegaly treated?
- if progesterone-induced –> Spay, d/c progestin medications. May also be able to reverse the DM if beta cells are not completely exhuasted by excessive GH
- Progesterone receptor blocker –> alepristone
- Leveothyroxine if it’s due to a primary hypothyroidism
- Medical management of somatotroph adenoma –> octreotide, lanreotide (somatostatin analogue), pegvisomant (GH-receptor blocker)
- RT, may not reverse endocrine dysfucntion
- Hypophysectomy
What is the mutation that causes canine pituitary dwarfism? Which breed is most at risk?
LHX-3
German Shepherds
What are the clinical manifestation of canine pituitary dwarfism?
Proportional dwarfism
- poor haircoat, eventual truncal alopecia
- hyperpigmented, scaly skin. Can have 2nd bacterial infection
- cryptorchids, no heat cycles
- active and alert, but decreased appetite and activity level by 2-3yo
- renal disease (GH and thyroxine is needed for proper development of the kidneys)
- LHX3 mutation is also associated with AA deformities
What lab abnormalities are noted?
Increased creatinine level
How is pituitary dwarfism in dogs diagnosed?
Stimulation test:
- lack of GH release with GHRH administration or alpha-adrenergic drugs (ex. clonidine, xylazine)
- if ghrelin can increase GH, then it’s not pituitary dwarfism
- just a decreased in IGF-1 alone is not enough
- can also have decrease in TSH and serum T4
Imaging:
- sometimes can have a pituitary cyst
DNA test
- assess LHX3 mutation
How is canine pituitary dwarfism treated?
Porcine GH supplementation –> 6-8 weeks to see some skin/hair improvement. watch for diabetes mellitus
Progesterone supplementation –> watch for AE: DM, pruritus, skin infections, skeletal maldevelopment, mammary tumours, acromegaly, DM, cystic endometrial hyperplasia
What’s the prognosis for pituitary dwarfism in dogs?
Poor without treatment
Guarded with properly treated
What’s the clinical signs associated with acquired GH deficiency in dogs?
Truncal alopecia, skin hyperpigmentation. Usually noted 1-3yo
poor to moderate response to GH heterologous or medroxyprogesterone
