Veterinary Information:
Canine Hypothyroidism

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Terminology: Canine hypothyroidism (hypoT4) is a common condition in dogs from 2-6 years old. It is caused by a decreased production of T4 (Thyroxine) and T3 (Triiodothyronine) by the thyroid gland. Rare in cats.

Thyroid Gland: The thyroid gland in dogs is normally not palpable. If enlarged, it can sometimes be palpated laterally from the 3-8 oesophageal cartilage rings. The thyroid gland uses iodine to produce the hormone thyroxin. Iodine deficiency (for instance in an all meat diet) can result in a struma (enlarged thyroid gland) with hypoT4. TSH (hormone released by the pituitary gland) stimulates the uptake of iodine by the thyroid gland, especially with decreased blood level concentrations of iodine.

Possible Thyroid Gland Pathologies:
-hypo function = hypoT4 (common condition in dogs)
-hyper function = hyperT4 (common condition in cats)
-neoplasias

Pathogenesis: Any malfunction in the hypothalamic-pituitary-thyroid axis can cause an insufficient amount of circulating thyroid hormones.

Hypothalamic-Pituitary-Thyroid Axis. This is a negative feedback axis in which Thyrotropin Releasing Hormone (TRH) produced by the hypothalamus induces the Pituitary Gland to release TSH. Thyroid Stimulating Hormone/Thyrotropin (TSH) modulates the release of T3 and T4 from the Thyroid Gland. TSH also has a negative feedback loop on the TRH release from the hypothalamus. T4 has a negative feedback loop on both the TRH release and the TSH release.

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Veterinary Information: Canine Hypothyroidism

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Veterinary Information:
Canine Hypothyroidism