Exam 8: L. 6: Pituitary/ADH; Parathyroid/Calcium

Question 1

Osmolality

Answer 1

Number of osmoles per kilogram of solvent

• biggest player = SODIUM
• osmoles draw water

Question 2

Antidiuretic hormone

Answer 2

1) ADH = vasopressin
- released by posterior pituitary
- action: conserve water

Question 3

Plasma osmolality

Answer 3

Most important stimulus for THIRST and ADH release

-1% increase in osmolality can cause ADH release

Question 4

ADH actions

Answer 4

1) systemic effects/multiple organs
2) kidney
- increase permeability to water ==> allows reabsorption of solute free water
- urine production decreases/urine osmolality increases
- plasma osmolality decreases

Question 5

Polyuria and polydipsia

Answer 5

1) polyuria: >50 ml/kg/day
(normal = 20-45 ml/kg/day)
2) polydipsia: >100 ml/kg/day
(normal: 20-70 ml/kg/day)

3) the vast majority of animals with PU/PD are polyuric* first
- polyuria leads to volume depletion ==> polydipsia develops to prevent dehydration (polydipsia is an appropriate body response)

Question 6

PU/PD differential diagnoses

Answer 6

1) osmotic diuresis
2) diabetes insipidus
3) acquired (secondary) nephrogenic DI
- something is interfering with ADH receptor
4) iatrogenic
5) renal medullary solute washout

Question 7

Osmotic diuresis

Answer 7

Increase in urinary solutes (i.e. glucose) pulls water = =>diuresis = =>hypovolemia = =>stimulates thirst = =>polydipsia

Example = diabetes mellitus, chronic renal failure

Question 8

Diabetes insipidus

Answer 8

1) nothing to do with glucose or insulin!!
2) syndrome is related to ADH**
3) 2 manifestations: central and nephrogenic
- central: hypothalamus/pituitary not producing ADH (rare)
- nephrogenic: kidney not responding to ADH (usually it is acquired/secondary)

Question 9

Acquired/secondary NDI

Answer 9

1) by far the largest category of DI
2) ADH and ADH receptors are present
3) problem: interference in normal interaction between ADH and the kidneys
4) PU/PD is typically severe

Question 10

Causes of secondary NDI

Answer 10

Pyometra, hypercalcemia, hepatic disease, hyperadrenocortiscism, pyelonephritis, hyperthyroidism Addison’s disease, polycythemia, acromegaly, hyperaldosteronism, hypokalemia

Question 11

Summarizing DI

Answer 11

1) most DI cases are acquired and nephrogenic
2) most are polyuric 1st, with polydipsia developing to prevent dehydration
3) usually limiting water is a BAD idea and may worsen the situation
4) do NOT limit water without knowing cause of PU/PD

Question 12

Iatrogenic causes of PU/PD

Answer 12

1) anticonvulsants (phenobarbital)
2) glucocorticoids
3) diuretics
4) DOCP
5) synthetic thyroid hormone supplements

Question 13

Renal medullary solute washout

Answer 13

1) loss of renal medullary solutes-sodium and urea
- loss of medullary hypertonicity
- impaired ability of nephron to concentrate urine
2) potential causes
- hepatic disease
- Addison’s disease
- chronic diuretic therapy

Question 14

Water deprivation test

Answer 14

Bottom line: determine if animal has the ability to concentrate urine

1) used to differentiate between:
- psychogenic polydipsia (rare)
- central diabetes insipidus (rare)
- primary nephrogenic diabetes insipidus (rare)

ABSOLUTELY MUST RULE OUT ALL OTHER CAUSES OF PU/PD BEFORE DOING THIS TEST

Take several days to perform this test-do not abruptly deprive a PU/PD dog of water

Question 15

Distribution of calcium

Answer 15

1) protein bound (primarily albumin) ~40%
2) complexed (with citrate, phosphate) ~10%
3) ionized ~50%
- biologically active form*
- most important form for feedback and maintenance!

Question 16

Calcium flux

Answer 16

1) ionized calcium affected by acid-base:
- alkalosis = increases protein binding = DECREASES ionized calcium
- acidosis = decreases protein binding = increases ionized calcium
2) ionized calcium is UNAFFECTED by hypoalbuminemia
- total serum calcium and protein bound forms will decrease
- protein bound calcium acts as “pool” for ionized form

Question 17

Actions of PTH

Answer 17

1) mobilizes calcium from bone
2) increases vitamin D conversion in kidney ==> increases INTESTINAL uptake of calcium
3) increases distal renal tubular resorption of calcium
4) increases renal phosphorus excretion

Question 18

Etiologies of hypercalcemia

Answer 18

1) HARD IONS
H = hyperparathyroidism
A = Addison's disease
R = renal disease
D = hypervitaminosis D
I = idiopathic (cats)
O = Osteolysis (not common)
N = neoplasia (VERY COMMON)
S = systemic granulomatous disease

• **most significant levels of hypercalcemia are seen with:
• malignancy/neoplasia
• primary hyperparathyroidism
• vitamin D toxicity***

Question 19

Clinical signs of hypercalcemia

Answer 19

1) PU/PD*
2) listlessness
3) urinary incontinence (secondary to PU/PD)
4) weakness
5) exercise intolerance
6) inappetence

Question 20

Primary hyperparathyroidism

Answer 20

1) excessive secretion of PTH
2) etiologies
- parathyroid adenoma (most common)
3) signalment
- >7 years of age
4) clinical signs solely due to hypercalcemia!!

Question 21

Remember

Answer 21

If a patient has hypercalcemia and the PTH level is at the upper end of normal, this is ABNORMAL!

Question 22

Diagnosis of hyperparathyroidism

Answer 22

Elevated PTH (+/- normal range) in face of hypercalcemia!!

Question 23

Therapy for hypercalcemia

Answer 23

1) IV fluid therapy
- saline diuresis at 2-3 times maintenance
2) diuretic therapy (furosemide)
- IF and ONLY IF fluid deficits have been replaced
3) glucocorticoid therapy (prednisone)
- IF and ONLY IF diagnosis has been made (if the hypercalcemia is due to lymphoma, the glucocorticoids may kill some of the lymphoma cells and make it hard to get diagnosis)

Question 24

Hypercalcemia of malignancy

Answer 24

1) dog
- lymphoma**
- anal sac adenocarcinoma
2) cat
- lymphoma
- squamous cell carcinoma

3) malignancy = most common cause of pathologic hypercalcemia in dogs and cats!!

Question 25

Clinical signs of hypocalcemia

Answer 25

1) seizure/tetany
2) hyperthermia (due to above)
3) tense abdomen, stiff gait, muscle fasciculations
4) cardiac arrhythmias
5) facial pruritus
- hypocalcemia
- methimazole treatment

most dogs present with acute signs, neurologic or neuromuscular

Question 26

Specific diagnosis of hypoparathyroidism

Answer 26

1) High index of suspicion when:
- profound hypocalcemia
- hypomagnesemia
- hyperphosphatemia
- normal renal parameters!
2) LOW to undetectable PTH level in HYPOCALCEMIA animal

Question 27

Emergency therapy: hypocalcemia

Answer 27

1) IV calcium administration
2) concurrent ECG monitoring
3) calcium gluconate
- 10% solution
- 1-1.5 ml/kg slowly
- infusion effects: 1-12 hours
4) monitor temperature

After emergency has passed, begin oral therapy: calcium, vitamin D