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  • Author or Editor: Peter A. Graham, x
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Abstract

Objective—To evaluate response of euthyroid cats to administration of recombinant human thyroid-stimulating hormone (rhTSH).

Animals—7 healthy cats.

Procedure—Each cat received each of 5 doses of rhTSH (0, 0.025, 0.050, 0.100, and 0.200 mg), IV, at 1-week intervals. Serum concentration of total thyroxine (TT4) and free thyroxine (fT4) was measured immediately before each injection (time 0) and 2, 4, 6, and 8 hours after administration of each dose.

Results—Overall TT4 response did not differ significantly among cats when administered doses were ≥ 0.025 mg. Serum TT4 concentrations peaked 6 to 8 hours after administration for all doses ≥ 0.025 mg. For all doses ≥ 0.025 mg, mean ± SEM TT4 concentration at 0, 6, and 8 hours was 33.9 ± 1.7, 101.8 ± 5.9, and 101.5 ± 5.7 nmol/L, respectively. For all doses ≥ 0.025 mg, mean fT4 concentration at 0, 6, and 8 hours was 38.7 ± 2.9, 104.5 ± 7.6, and 100.4 ± 8.0 pmol/L, respectively. At 8 hours, the fT4 response to 0.025 and 0.050 mg was less than the response to 0.100 and 0.200 mg. Adverse reactions after rhTSH administration were not detected.

Conclusions and Clinical Relevance—The TSH stimulation test can be performed in cats by IV administration of 0.025 to 0.200 mg of rhTSH and measurement of serum TT4 concentrations at time of injection and 6 or 8 hours later. Clinical validation of the TSH stimulation test would facilitate development of additional tests of thyroid gland function, such as a TSH assay. (Am J Vet Res 2003;64:149–152)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine prevalence of thyroid hormone autoantibodies (THAA) in serum of dogs with clinical signs of hypothyroidism.

Design—Cohort study.

Sample Population—287,948 serum samples from dogs with clinical signs consistent with hypothyroidism.

Procedure—Serum THAA were detected by use of a radiometric assay. Correlation and X 2 analyses were used to determine whether prevalence varied with breed, age, sex, or body weight. Only breeds for which ≥ 50 samples had been submitted were used for analysis of breed prevalence.

Results—Thyroid hormone autoantibodies were detected in 18,135 (6.3%) samples. The 10 breeds with the highest prevalence of THAA were the Pointer, English Setter, English Pointer, Skye Terrier, German Wirehaired Pointer, Old English Sheepdog, Boxer, Maltese, Kuvasz, and Petit Basset Griffon Vendeen. Prevalence was significantly correlated with body weight and was highest in dogs between 2 and 4 years old. Females were significantly more likely to have THAA than were males.

Conclusions and Clinical Relevance—Thyroid hormone autoantibodies may falsely increase measured triiodothyronine (T3) and thyroxine (T4) concentrations in dogs; results suggest that T3 concentration may be falsely increased in approximately 57 of 1,000 dogs with hypothyroidism and that T4 concentration may be falsely increased in approximately 17 of 1,000 dogs with hypothyroidism. Results also suggested that dogs of certain breeds were significantly more or less likely to have THAA than were dogs in general. (J Am Vet Med Assoc 2002;220:466–471)

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To compare effects of short-term administration of a soy diet with those of a soy-free diet on serum thyroid hormone concentrations in healthy adult cats.

Animals—18 healthy adult cats.

Procedure—Cats were randomly assigned to receive either a soy or soy-free diet for 3 months each in a crossover design. Assays included CBC, serum biochemical profile, thyroid hormone analysis, and measurement of urinary isoflavone concentrations.

Results—Genistein, a major soy isoflavone, was identified in the urine of 10 of 18 cats prior to dietary intervention. Compared with the soy-free diet, cats that received the soy diet had significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations. The T3/fT4 ratio was also significantly lower in cats that received the soy diet. Although the magnitudes of the increases were small (8% for T4 and 14% for fT4), these changes resulted in an increased proportion of cats (from 1/18 to 4/18) that had fT4 values greater than the upper limit of the laboratory reference range. There was no significant effect of diet on any other measured parameter.

Conclusions and Clinical Relevance—Short-term administration of dietary soy has a measurable although modest effect on thyroid hormone homeostasis in cats. Increase in T4 concentration relative to T3 concentration may result from inhibition of 5'-iodothyronine deiodinase or enhanced T3 clearance. Soy is a common dietary component that increases serum T4 concentration in cats. ( Am J Vet Res 2004; 65:586–591)

Full access
in American Journal of Veterinary Research

Abstract

In collaboration with the American College of Veterinary Pathologists

Open access
in Journal of the American Veterinary Medical Association