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Abstract

Objective

To document circulating total thyroxine (T4) and triiodothyronine (T3) responses after administration of thyrotropin (thyroid-stimulating hormone [TSH]) to hyperthyroid and healthy cats and assess the value of these responses as an additional diagnostic test for hyperthyroidism.

Design

Prospective case series.

Animals

21 healthy and 40 hyperthyroid cats.

Procedure

Serum total T4 and T3 concentrations were measured by radioimmunoassay before and 6 hours after administration of 0.5 IU of bovine TSH/kg of body weight.

Results

In healthy cats, serum total T4 concentration increased after administration of TSH (mean ± SD, 114.0 ± 36.4 nmol/L) representing a mean increment 3 times baseline concentration (mean ± SD, 33.7 ± 7.6 nmol/L). In hyperthyroid cats, the relative increase in serum total T4 concentration was significantly (P < 0.001) different; baseline values (mean ± SD, 236.2 ± 146.0 nmol/L) increased minimally after TSH administration (mean ± SD, 308.1 ± 178.9 nmol/L). There was a significant negative correlation (r s = −0.366) between relative increase in serum total T4 concentration after TSH administration and baseline concentration in hyperthyroid cats. In 3 cats with equivocal baseline serum total T4 concentration the T4 response to TSH administration was indistinguishable from that in healthy cats. Serum total T3 response to TSH administration was significantly (P < 0.001) lower in hyperthyroid, compared with healthy, cats but the T3 response in healthy cats was more variable than that for T4.

Conclusions

Thyrotoxic cats with high baseline serum total T4 concentration have a limited T4 response to TSH stimulation. Hyperthyroid cats with equivocal baseline serum total T4 concentrations have T4 responses after TSH stimulation similar to those of healthy cats. Measurement of serum total T3 concentration provides no additional information.

Clinical Relevance

The TSH response test is of limited value in diagnosing hyperthyroidism in cats. (Am J Vet Res 1996;57:987–991)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To assess selenium (Se) status of cats in 4 regions of the world and to compare results for Se status with reported incidence of hyperthyroidism in cats in those regions.

Animals—50 cats (30 from 2 regions with an allegedly high incidence of hyperthyroidism and 20 from 2 regions in which the disease is less commonly reported).

Procedure—Hematologic samples (heparinized whole blood, plasma, and RBC fractions) were obtained from 43 healthy euthyroid cats and 7 hyperthyroid cats. Plasma concentration of Se and activity of glutathione peroxidase (GPX) in whole blood and plasma were determined.

Results—Plasma concentration of Se and GPX activity in whole blood or plasma did not differ significantly among cats from the 4 regions. However, cats had a plasma concentration of Se that was approximately 10 times the concentration reported in rats and humans. The GPX activity in whole blood or plasma in cats generally was higher than values reported in rats or humans.

Conclusions and Clinical Relevance—Cats have higher Se concentrations in plasma, compared with values for other species. However, Se status alone does not appear to affect the incidence of hyperthyroidism in cats. High Se concentrations may have implications for health of cats if such concentrations are influenced by the amount of that micronutrient included in diets. (Am J Vet Res 2001;62:934–937)

Full access
in American Journal of Veterinary Research