Serum triiodothyronine, total thyroxine, and free thyroxine concentrations in horses.
Abstract: The objectives of this experiment were to determine serum concentrations of triiodothyronine (T3), thyroxine (T4), and free thyroxine (fT4) at rest, following thyroid-stimulating hormone (TSH) administration, and following phenylbutazone administration in healthy horses. This was done to determine which available laboratory test can best be used for diagnosis of hypothyroid conditions in horses. Serum T3, T4, and fT4 concentrations in serum samples obtained before and after TSH stimulation and following phenylbutazone administration for 7 days were determined. Baseline values ranged from 0.21 to 0.80 ng of T3/ml, 6.2 to 25.1 ng of T4/ml, and 0.07 to 0.47 ng of fT3/dl. After 5 IU of TSH was administered IV, serum T3 values increased to 6 times baseline values in 2 hours. Thyroxine values increased to 3 times baseline values at 4 hours and remained high at 6 hours. Free T4 values increased to 4 times baseline values at 4 hours and remained high at 6 hours. Administration of 4.4 mg of phenylbutazone/kg, every 12 hours for 7 days significantly decreased T4 and fT4 values, but did not significantly affect serum T3 concentrations. It was concluded that a TSH stimulation test should be performed when hypothyroidism is suspected. Measurement of serum fT4 concentrations, by the single-stage radioimmunoassay, does not provide any additional information about thyroid gland function over that gained by measuring T4 concentrations. Phenylbutazone given at a dosage of 4.4 mg/kg every 24 hours, for 7 days did significantly decrease resting T4 and fT4 concentrations, but did not significantly affect T3 concentrations in horses.
Publication Date: 1993-01-01 PubMed ID: 8427472
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- Journal Article
Summary
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This study investigates the levels of key thyroid hormones in horses under rest, after inducing thyroid activity, and after administration of a specific drug. The research aimed to identify the best method for detecting hypothyroid conditions in horses.
Objective and Methodology of the Study
- The primary aim of this study was to establish the different levels of triiodothyronine (T3), thyroxine (T4), and free thyroxine (fT4) – important chemicals in the thyroid that influence metabolism and other body functions – under various conditions in healthy horses.
- The experiment was conducted to understand which laboratory test is the most reliable for detecting hypothyroidism (a condition where the thyroid gland is underactive) in horses.
- The researchers measured these hormone levels under three conditions: at rest, after the administration of thyroid-stimulating hormone (TSH) that naturally induces thyroid activity, and after providing the horses with a drug known as phenylbutazone for a week.
Results and Findings
- Based on their findings, the baseline values for the hormones varied: T3 levels ranged from 0.21 to 0.80 ng/ml, T4 levels from 6.2 to 25.1 ng/ml, and fT3 levels from 0.07 to 0.47 ng/dl.
- The administration of TSH resulted in a significant increase in all the hormone levels. Serum T3 values increased up to six times the baseline values within two hours, and both T4 and fT4 values increased to around three to four times their baseline values within four hours and stayed high for another two hours.
- However, administering the drug phenylbutazone every 12 hours for seven days significantly reduced T4 and fT4 levels, but did not significantly affect the T3 concentrations.
Implications of the Study
- The findings indicated that a TSH stimulation test should be performed when suspecting hypothyroidism in horses as it showed a significant and observable increase in all the hormone levels tested.
- Furthermore, the study concluded that measuring serum fT4 concentrations using the single-stage radioimmunoassay provides no additional information about thyroid function over that gained by the measurement of T4 concentrations.
- Another key insight from this research was that long-term administration of phenylbutazone significantly decreased resting levels of T4 and fT4 but did not have a substantial impact on T3 concentrations in horses.
Cite This Article
APA
Sojka JE, Johnson MA, Bottoms GD.
(1993).
Serum triiodothyronine, total thyroxine, and free thyroxine concentrations in horses.
Am J Vet Res, 54(1), 52-55.
Publication
Researcher Affiliations
- Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, IN 47907.
MeSH Terms
- Analysis of Variance
- Animals
- Female
- Horses / blood
- Male
- Phenylbutazone / pharmacology
- Thyrotropin / pharmacology
- Thyroxine / blood
- Thyroxine / drug effects
- Triiodothyronine / blood
- Triiodothyronine / drug effects
Citations
This article has been cited 2 times.- Tangyuenyong S, Nambo Y, Nagaoka K, Tanaka T, Watanabe G. Sensitive radioimmunoassay of total thyroxine (T4) in horses using a simple extraction method.. J Vet Med Sci 2017 Jul 28;79(7):1294-1300.
- Hilderbran AC, Breuhaus BA, Refsal KR. Nonthyroidal illness syndrome in adult horses.. J Vet Intern Med 2014 Mar-Apr;28(2):609-17.
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