Function Tests 2

Question 1

Dexamethasone Supression Test

Answer 1

1) Evaluates adrenal glands differently using feedback loop
2) Dexamethasone is a glucocorticoid. In normal animals, injection should suppress ACTH release from pituitary. Would see a decrease in cortisol levels.
3) Low Dosage Test
4) High Dosage Test

Question 2

Low Dosage Test

Answer 2

a) Confirms or replaces ACTH test for hyperfunction. Differentiates normal from hyper.
b) Hypercorticism animal resistant to suppression by small dosage
c) Diseased pituitary insensitive to small amounts of dex = increased ACTH = increased cortisol
d) If adrenal glands are releasing increased levels of cortisol, adding more cortisol doesn’t matter. ACTH has already been suppressed.

Question 3

High Dosage Test

Answer 3

a) Goes further, differentiates pituitary from adrenal causes for hyperfunction
b) Sensitivity of diseased pituitary to dex is incomplete: Large doses overcome it and ACTH is suppressed, cortisone levels will fall.
c) If adrenals are abnormal, they will continue to secrete cortisol

Question 4

Summnary of Dexamethasone Supression Test

Answer 4

a) If unresponsive to all dex dosage = primarily adrenal gland disease
b) If suppression by large dose, but not small = pituitary problem

Question 5

Hypothyroidism

Answer 5

Hypothyroidism is common in dogs, horses, ruminants, and swine
a. In young animals = dwarfism (cretinism) – affects all systems in the body
b. Decreased metabolism, lethargy, hair loss,
weight gain, edema, reproductive failure

Question 6

Hyperthyroidism

Answer 6

Hyperthyroidism is common in cats (and Giant Schnauzers)

a. Increased metabolism, weight loss with normal or increased appetite
b. Irritability, nervousness

Question 7

Thyroid Feedback loop

Answer 7

Hypothalamus-(TRF-Thyrotropin Releasing Factor) Pituitary – TSH 
Thyroid- Thyroxine (T4) 80% - ½ converted to T3 (slower) Hypothalamus …
20% immediately gets converted to T3 – Tissues (More stimulating to cells)
–T3 The cells really like them

Question 8

Thyroid Function

Answer 8

Thyroid hormones influence metabolic rate, growth, and differentiation of body cells

Question 9

Routine T4 tests measure…

Answer 9

Routine T4 tests measure both protein bound and free T4 (99% circulating T4 is bound)

Question 10

TSH Response Test

Answer 10

a. Normal vs. Abnormal
b. Usually used in hypothyroid/dogs
d. Should see increased T4 in normal animals
Hypothyroid = no increase in T4
Hyperthyroid – oddly little to no increase. Thyroid functioning independently. Diagnosis comes from clinical signs, increased baseline T4 and/or lack of TSH response.

Question 11

TSH Response Test Protocol

Answer 11

1) Baseline T4
2) TSH IV – 4-6 hours
3) T4