EFFECTS OF LEVOTHYROXINE ADMINSTRATION AND WITHDRAWAL ON THE HYPOTHALAMIC-PITUITARY-THYROID AXIS IN EUTHYROID DOGS

摘要

Many dogs are misdiagnosed with hypothyroidism because of the vague presenting signs and limitations of thyroid function tests, leading to inappropriate treatment with levothyroxine. During chronic supplementation, the hypothalamiic-pituitary-thyroidaxis (HPTA) is suppressed and may make it difficult to accurately determine thyroid function following withdrawal of levothyroxine. We sought to determine if the HPTA is suppressed following levothyroxine administration in euthyroid dogs and the time required for resolution of any suppression. We hypothesized that levothyroxine administration would suppress the HPTA in euthyroid dogs and that the HPTA would recover within 8 weeks in all dogs, regardless of the duration of treatment.