Endocrinology Flashcards
From what structure does the anterior lobe of the pituitary develop?
Adenohypophysis (which develops from Rathke’s pouch)
From what structure does the posterior pituitary develop?
Neurohypophysis
The neurohypophysis is an extension of what?
The hypothalamus
T/F: The anterior pituitary is a collection of nerve endings that stores and releases hormones produced by the hypothalamus.
False: it’s the POSTERIOR pituitary that does this
What are the five cell types of the anterior pituitary?
- Corticotrophs
- Thyrotrophs
- Gonadotrophs
- Somatotropin’s
- Lactotrophs
What hormone from the hypothalamus stimulates corticotrophs and what does it cause them to release?
Corticotropin-releasing hormone (CRH) stimulates them to release adrenocorticotropic hormone (ACTH)
What hormone from the hypothalamus stimulates thyrorophs and what does it cause them to release?
Thyrotropin-releasing hormone (TRH) stimulates them to release thyroid-stimulating hormone (TSH)
What hormone from the hypothalamus stimulates gonadotrophs and what does it cause them to release?
Gonadotropin-releasing hormone (GnRH) stimulates them to release leuteinizing hormone (LH) and follicle stimulating hormone (FSH)
What hormone from the hypothalamus stimulates somatotrophs and what does it cause them to release?
Growth hormone-releasing hormone (GHRH) stimulates them to release growth hormone (GH)
What hormone from the hypothalamus stimulates lactotrophs and what does it cause them to release?
It’s unknown what acts on lactotrophs to stimulate release, but they secrete prolactin
What is the inhibitory hormone of somatotrophs?
Somatostatin (aka growth hormone inhibitory hormone). It is the same somatostatin that is found in the GIT, just located in the brain
What is the inhibitory hormone that acts on lactotrophs?
Prolactin inhibitory hormone (PIH)
Does the posterior pituitary produce hormones?
NO - it stores and releases hormones produced in the supraoptic and paraventricular nuclei of the hypothalamus
What hormone is produced by the supraoptic nuclei and what is its function?
Vasopressin/antidiuretic hormone (ADH) —> acts on V2 receptors in the collecting ducts of the nephron which results in insertion of aquaporin-2 channels for reabsorption of water
What hormone is produced by the paraventricular nuclei and what is its function?
Oxytocin —> causes uterine contraction, lactation, and promotes maternal nurturing behavior
Growth hormone is also known as what?
Somatotropin
What are the functions of growth hormone?
- Increase protein synthesis
- Increase mobilization of fatty acids from adipose tissue —> lipolysis and fatty acid oxidation (protein-sparing effect) during fasting
- Decreased utilization of glucose throughout the body
What molecule mediates most actions of growth hormone?
Insulin-like growth factors (IGFs) aka somatomedins
Where is IGF-1 predominantly made?
Liver —> will be produced in response to GH
Development of IGF-1 within the liver from the action of growth hormone is dependent on what?
Insulin
If you have a diabetic that has not been treated with insulin yet they could have falsely low IGF-1 levels just because there isn’t enough insulin in the portal vein
IGF-1 has inhibitory effects on GH production through what effects?
- Direct inhibition of GH
- Upregulation of somatostatin which will result in decreased GH production by the hypothalamus
What hormone will influence release of GH from the pituitary?
Ghrelin
GH predominates in the __ state
Fasting
GH has insulin __
Antagonism
Insulin-like activity INCREASES/DECREASES in response to IGF-1
Increases
What non-hormone factors stimulate growth hormone secretion?
- Decrease BG
- Decreased FFA
- Increased amino acids
- Starvation, fasting, protein deficiency
- Trauma, stress, excitement
- Exercise
- Testosterone, estrogen
- Deep sleep (stages II, IV)
Remember hormones are GHRH and ghrelin
What non-hormone factors inhibit GH secretion?
- Increased BG
- Increased FFA
- Aging
- Obesity
Remember hormones are GHIH (somatostatin) and Somatomedins (IGFs)
Pituitary dwarfism is also known as
Congenital hyposomatotropism
What dog breeds are typically associated with pituitary dwarfism?
GSDs, Karelian bear dogs, saaroloos wolfhound, Czechoslovakian wolf dog
**Rare in cats
What mutation is associated with pituitary dwarfism and how is it inherited?
LHX3 mutation, autosomal recessive
What is the pathophysiology of pituitary dwarfism?
Pituitary cysts or pituitary hypoplasia —> unclear if the cysts cause the hypoplasia or are a consequence of it
In GSDs with pituitary dwarfism, what hormone abnormalities might you find on screening tests?
Combined GH, TSH, and prolactin deficiency
What age do pituitary dwarfism patients typically present?
3-5 months of age
What are common musculoskeletal clinical signs associated with pituitary dwarfism?
Musculoskeletal:
- Proportionate growth failure (unlike congenital hypothyroidism where short legs and big head)
- Pointed nose/fox like facial features
- Delayed closure of growth plates
- Delayed dental eruption
What are common dermatologic clinical signs associated with pituitary dwarfism?
Dermatological:
- Soft woolly hair coat
- Lack of guard hairs
- Hair loss (areas of wear - collar, sitting)
- Hyperpigmented, scaly, thin wrinkled skin
- Papules, pyoderma, comedones
What are common reproductive clinical signs associated with pituitary dwarfism?
- Cryptorchidism
- Testicular atrophy
- Persistent anestrus
What CBC and chem findings might you find with pituitary dwarfism?
**Often normal, but may see
CBC: mild anemia due to hypothyroidism
Chem: hypophosphatemia (b/c of changes happening at bone), hypoalbuminemia, azotemia (develops over time)
How is pituitary dwarfism diagnosed?
Genetic testing for LHX2 —> if positive, no further testing needed
Growth hormone stimulation test —> GH measurement after stimulation with GHRH, colonizing, xylazine, ghrelin DIFFICULT TO PERFORM
How is pituitary dwarfism treated in dogs?
- Human-recombinant, porcine, ovine, or bovine GH supplementation (usually porcine b/c it’s the most genetically similar)
- Progesterone —> induces GH synthesis in the mammary gland
No protocols described in cats
Response: Often see regrowth of secondary hair, some dogs may develop a full hair coat. May see linear growth determined by status of growth plates at time of therapy (although typically very little improvement).
Risk of treatment leading to DM b/c of progesterone
Prognosis: guarded even with treatment; dogs usually euthanized by 3-5y of age if not treated
Hypersomatotropism is also known as
Acromegaly
What is the typical signalment of an acromegalic patient?
Feline
~10y
Male (88%)»_space;> female
DSH > DLH
What is the pathophysiology of acromegaly in CATS?
GH-producing acidophil pituitary adenoma —> produces too much GH —> increased IGF-1 levels resulting in proliferation of bone, cartilage, soft tissues, and and increased size of organs
Despite increased IGF-1 levels, acromegalic cats are typically still insulin resistant. Why?
The increased IGF-1 levels are unable to counteract insulin-resistance induced by excessive GH concentrations —> the GH is too excessive they can’t convert enough GH to IGF-1
What are common clinical signs of acromegaly in cats
Think DM signs: PU/PD, plantigrade stance, polyphagia (from DM and the excessive production of GH)
Also broadening of head, prognathia inferior, widening of interdental spaces, respiratory stridor +/- distress (due to increased/thickening of oropharyngeal tissue), CNS signs
WEIGHT PATTERNS ARE HUGE CLUE
Typically these cats will lose weight due to the secondary DM but stabilize with super high doses of insulin and then actually gain weight which doesn’t usually happen in uncontrolled diabetics
At what dose of insulin should you start questioning if a cat has acromegaly?
When you get above 2 units/kg q12h
What organs typically become enlarged in acromegalic cats?
Heart
Kidneys
Spleen
Pancreas
Adrenals
Thyroid
What percentage of cats with acromegaly can have neurologic signs?
10-15%
What abnormalities might you see on CBC in an acromegalic cat?
Relative erythrocytosis due to dehydration
What abnormalities may you see on chemistry panel in an acromegalic cat?
- Hyperglycemia
- Hyperproteinemia (due to dehydration)
- Mild increases in ALT and ALP activity (due to mobilization of fats and sugars that cause hepatocytes to swell —> vacuolar change)
- Hyponatremia b/c glucose pulls more water into vascular space to dilute out sodium
- Hyperphosphatemia without azotemia (GH/IGF-1 mediates increased renal tubular absorption of phosphorus; will look like decreased GFR without azotemia)
- Azotemia (50% of acromegalic cats develop CKD within 8-36m of diagnosis; mechanism not fully understood but may be due to glucosuria causing glomerulopathy)
What abnormalities might you see on a UA with an acromegalic cat?
- Glucosuria
- Proteinuria (when azotemia present)
When should you consider testing for acromegaly?
Cats with difficult to regulate DM in which other common concurrent problems (stomatitis/gingivitis/UTIs, corticosteroid administration) have been eliminated
Remember >2U/kg of insulin q12h
What is the diagnostic test of choice for acromegaly?
IGF-1 measurement
Why is IGF-1 measurement preferred for diagnosis of acromegaly in cats?
- Reflects 24h GH secretion
- Is not secreted in pulses (unlike GH) so single random sampling is sufficient
- Structure is conserved across species, so more assay availability (unlike GH)
- Stable, so serum sample can be sent by regular mail (GH cannot)
What concurrent disease can decrease IGF-1 making interpretation of the assay difficult if acromegaly is of concern?
- Malnutrition
- Liver failure
- Renal failure
- Hypothyroidism
- Poorly controlled DM
- Oral estrogen intake
Why might IGF-1 be normal when assessed prior to starting insulin therapy in acromegalic diabetic cats?
Remember IGF-1 is produced because of insulin in the portal vein —> in cats with diabetes, it may be low because there is not enough insulin available to stimulate IGF-1 production
If IGF-1 is normal in a cat you suspect has acromegaly and you have not yet started insulin, when should you recheck?
6-8 weeks after insulin therapy is initiated
What is the “gray zone” for IGF-1 testing?
800-1000ng/mL - if in this range and suspicion for acromegaly is high, consider pituitary imaging
What are goals of treatment of acromegaly?
Two goals:
1. Treat acromegaly (sx, SRT)
2. Treat concurrent DM
T/F: Pituitary surgery is the gold standard for treatment of acromegaly
TRUE - but technically demanding, one study showed remission of DM in a cat 3 weeks after surgery
What medications are used to decrease GH secretion?
Somatostatin analogs (octreotide, lanreotide, pasireotide)
Also dopamine agonist L-deprenyl
All showed very little effect EXCEPT pasireotide
A 2017 study (Gostelow et al, JVIM) showed which somatostatin analong to be most effective in treatment of acromegaly?
Pasireotide
A 2017 study (Gostelow et al, JVIM) showed long-acting pasireotide induced diabetic remission in 3/8 cats
SRT shows improvement in symptoms and improved control of DM in what percentage of cats?
Improvement of symptoms in 2/3 of cats
Improved control of DM in 50-92% of cats
What is prognosis for acromegaly with and without treatment?
Guarded to poor if not treated (months)
If they have pituitary surgery or SRT - favorable outcomes, MST 25m
What is the etiology of acromegaly in DOGS?
Almost always induced by endogenous or exogenous progestogens giving rise to GH hypersecretion from the mammary gland
AKA they’re either getting progesterone or have a progesterone-secreting tumor in the mammary glands
What breeds of dogs are predisposed to acromegaly?
Swedish and Norwegian Elkhounds
Border collies
Beagles
T/F: GH-producing tumors in the pituitary gland of dogs resulting in acromegaly are very common
FALSE - very rare, opposite of cats
Somatotrophic adenoma only described in 2 dogs
What is the treatment for acromegaly in dogs?
If diestrus-associated acromegaly in intact females: OHE
If due to exogenous progesterone - stop giving them
If a mass producing progesterone - remove the mass
What are the three zones of the adrenal cortex and what do they produce?
- Zona glomerulosa - mineralocorticoids (aldosterone)
- Zona fasciculata - glucocortocoids (cortisol)
- Zona reticularis - sex hormones (progesterone, estrogens, androgens)
“The deeper you go the better it gets”
Salt —> sugar —> sex
All hormones produced by the adrenal cortex are derived from what molecule?
Cholesterol
Conversion of cholesterol to aldosterone is regulated by what enzyme?
Aldosterone synthase
Zona glomerulosa is rich in aldosterone synthase
Conversion of cholesterol to glucocorticoids (cortisol) and sex hormones is regulated by what enzyme?
17a hydroxylase Aka cholesterol desmolase
Zona faciculata and reticularis are both rich in this enzyme (inhibitors of this enzyme exist in people)
T/F: Trilostane is a 17a hydroxylase inhibitor
FALSE - it’s a competitive inhibitor of 3beta-hydroxysteroid dehydrogenase
What is the half life of corticotropin-releasing hormone (CRH) in plasma?
~60 minutes
CRH produced in the __ is released by the __ and acts on __ in the __. This stimulates release of __ which stimulates secretion of __ from the adrenal gland.
CRH produced in the PARAVENTRICULAR NUCLEI is released by the HYPOTHALAMUS and acts on CORTICOTROPHS in the ANTERIOR PITUITARY. This stimulates release of ACTH which stimulates secretion of GLUCOCORTICOIDS from the adrenal gland.
Adrenocorticotropic hormone (ACTH) is derived from what?
POMC - proopiomelanocortin
What is the half life of ACTH in plasma?
~10min
T/F: ACTH causes some secretion of mineralocorticoids and sex hormones, but to a lesser extent than glucocorticoids
True
What hormone provides negative feedback on the hypothalamic-pituitary-adrenal axis?
Cortisol
Why does elevated cortisol result in elevated blood glucose?
Causes increase in gluconeogenesis and decrease in insulin responsiveness and production, and decreases glucose utilization b/c there’s less insulin in circulation
What are the five effects of cortisol?
- Increased blood glucose
- Decreased insulin sensitivity
- Increased protein mobilization
- Increased mobilization of fat
- Decreased inflammation and immune system function
How does cortisol cause increased protein mobilization?
Decrease in cellular proteins while increasing production of proteins from liver and in plasma
How does increased cortisol decrease inflammation and immune system function?
- Decreases expression of adherence molecules on sides of blood vessels —> less migration of WBCs into interstitium
- Decreases permeability of capillaries —> less diapedesis
- Decreases lymphocyte production —> lymphopenia on stress leukogram
- Increases lysosome stabilization w/in phagocytes —> less able to fight off pathogens
What does the SMILED acronym for a stress leukogram mean?
Segs, monos increased
Lymphs, eos decreased
Do the majority of dogs have adrenal or pituitary dependent hyperadrenocorticism?
Pituitary-dependent (PDH) —> 85% have pituitary tumors
What percentage of dogs with hyperadrenocorticism have adrenal tumors?
15%
Iatrogenic hyperadrenocorticism result from?
Exogenous steroid administration
Bilaterally adrenomegaly is associated with ADH or PDH?
PDH - increased ACTH stimulation from pituitary acts on both adrenals
Negative feedback loop from cortisol doesn’t work
Unilateral adrenomegaly with atrophy of the contralateral adrenal gland is consistent with ADH/PDH?
ADH
Negative feedback loop from cortisol still works and you get decreased ACTH production to act on the unaffected adrenal gland
Canine Pituitary tumors are commonly adenoma or carcinomas?
Adenomas (carcinomas are rare)
Are most pituitary adenomas more commonly micro or macro and what is the size cutoff?
Most commonly microadenomas (<10mm)
Macroadenoma = >10mm
What percentage of dogs at diagnosis of a pituitary adenoma have a tumor <3mm?
21-48%
Adrenal tumors are commonly UNILATERAL/BILATERAL
Unilateral
Adrenal tumors > ___cm are more likely to be carcinomas
> 2cm
Also those that are invading regional vasculature
What is the common signalment of patients with hyperadrenocorticism?
Dogs
Middle aged to older (>= 89% older than 6y)
Poodles, Dachshunds, terriers, Beagles, GSDs, Labs
ADH/PDH tends to occur more in smaller dogs, and ADH/PDH tends to occur more in larger dogs
PDH in smaller dogs
ADH in larger dogs
What breeds are more commonly associated with PDH?
Poodles
Dachshunds
Terriers
Beagles
What breeds are more commonly associated with ADH?
Poodles
GSDs
Dachshunds
Labradors
How does hyperadrenocorticism result in polyuria?
Increased cortisol inhibits ADH’s action on V2 receptors leading to secondary nephrogenic diabetes insipidus, so you get polyuria
USG is <1.015, often less than 1.008
Why do dogs with hyperadrenocorticism get muscle wasting?
Cortisol causes protein catabolism
Why does calcinosis cutis develop with hyperadrenocorticism?
Cortisol causes secondary hyperparathyroidism (90% of dogs with HAC have high PTH) —> leads to Ca & Phos deposition
Why do dogs with HAC get hepatomegaly?
Cortisol causes increased protein, fat, and glucose mobilization —> vacuolar hepatopathy —> hepatomegaly
Why do dogs with HAC get a “pot bellied” appearance
Hepatomegaly, weakened abdominal muscles, abdominal fat accumulation, enlarged bladder from polyuria all contribute
Why do dogs with HAC have increased panting?
Weakened respiratory muscles, hepatomegaly, and decreased lung compliance (from pulmonary/bronchial mineralization) all contribute
What CBC changes may you see in dogs with HAC?
- “Stress Leukogram” - SMILED
- Neutrophilia and monocytosis from steroid-enhanced demargination
- Lymphopenia from steroid-induced lymphocytes
- Eosinopenia from bone marrow sequestration of eosinophils - Mild polycythemia - cortisol tells BM to make more RBCs
- Thrombocytosis (75-80% of dogs) - cortisol tells BM to make more platelets
What chemistry changes can be seen with HAC?
- Liver enzyme changes
- ALP»_space;> ALT (80-90%) due to corticosteroid induced ALP (cALP) coming from bile canilicular membranes of hepatocytes
- Mild ALT increase (<500U/L) b/c of swelling of hepatocytes from the vacuolar hepatopathy - Hypercholesterolemia and hypertriglyceridemia b/c cortisol results in lipolysis
- Results in lipemia
What UA changes might you see in a dog with HAC?
- Hyposthenuria to isosthenuria - USG <1.020 but often <1.008
- Proteinuria - occurs in >50% of dogs with HAC
- Usually UPC <5, and they never get secondary hypoalbuminemia
- Glomerulosclerosis, glucocorticoid-induced glomerular hypertension - UTIs - found in 50% of dogs with hyperadrenocorticism, but <5% have clinical signs of infection (relates to decreased diapedesis of WBCs)
What changes to pre- and post-bile acids may you see with HAC?
May be mildly increased, occurs in about 30% of dogs with HAC
T/F: 55% of HAC dogs without pancreatitis can have positive SNAP cPLs
True
cPLI has been shown to be HIGHER/LOWER In dogs with HAC who do not have pancreatitis
HIGHER
Basically don’t assume they have active panc if you’re suspicious of HAC
Why do dogs with HAC often have a secondary hypothyroidism?
Cortisol alters thyroid hormone binding to plasma proteins, metabolizes thyroid hormone and decreases peripheral deionization of T4 and T3
What percentage of dogs with HAC have hypertension, and what is the proposed mechanism?
31-86%
Etiology is unclear but thought to result from increased sensitivity to norepinephrine
What potential complication of HAC is the primary driver for treatment?
Development to PTEs
T/F: A urine cortisol:creat ratio can diagnose Cushings
NO - used to think it would help rule it out, but even that is not as sensitive
Sensitivity used to be 99%, new study showed 75%
Low specificity
What test is the only way to diagnose iatrogenic Cushings?
ACTH stim test (dog will have PU/PD and ALP, but ACTH stim looks like Addisonian)
What is Cortrosyn?
ACTH
What is the cutoff for an “exaggerated” response on a post sample of the ACTH stim test that would indicate Cushings disease?
<22ug/dL
Post-ACTH values:
Normal: <18ug/dL
Grey zone: 18-22ug/dL **if the patient has clinical signs and falls in this value, either do a LDDST or new guidelines say ok to assume they’re Cushinoid
Exaggerated: >22ug/dL
Steps for interpreting LDDST
- Look at 8h mark to determine who is Cushinoid - if cortisol is >1.4ug/dL, they’re Cushinoid
- Look at 4h mark - if they suppress <1.4ug/dL, it’s definitely pituitary dependent OR if 4 or 8h is <50% of baseline, it’s PDH
Remember adrenal dependent is overproduction of ACTH and negative feedback is not intact, so they don’t care if you give more cortisol
T/F: You can use a high dose dex suppression test to determine if a dog has HAC or not
NO - it is a differentiating test - it will NOT tell you if a dog has Cushing’s or not, must do a LDDST prior for this