Cardiovascular effects of equine hypothyroidism

摘要

Hypothyroidism occurs via either primary, secondary, or tertiary mechanisms. Characterization of these mechanisms in horses has essentially been borrowed from human and canine studies; mechanisms of equine hypothyroidism remain poorly studied. Resting thyroid hormone plasma/serum concentrations are routinely used, perhaps inappropriately, in equine practice for diagnosis of equine hypothyroidism. The validity of the use of resting thyroid plasma/serum concentrations has been challenged,particularlysince only 5 days of oral phenylbutazone therapy causes artificially-lowered plasma thyroid concentrations, presumably due to displacement of thyroid hormone from plasma protein binding sites and subsequent negative feedback at the anterior pituitary. Thyroid gland stimulation studies are required to provide more accurate and definitive diagnosis of hypothyroidism.