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Altered expression of G proteins in thyroid gland adenomas obtained from hyperthyroid cats

Kimberly B. HammerDepartment of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104- 6010.

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David E. HoltDepartment of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104- 6010.

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Cynthia R. WardDepartment of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104- 6010.

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Abstract

Objective—To determine whether expression of G proteins (Gi and Gs) is altered in thyroid gland adenomas obtained from hyperthyroid cats.

Sample Population—Adenomatous thyroid glands obtained from 8 hyperthyroid cats and thyroid glands obtained from 4 age-matched euthyroid cats.

Procedure—Expression of Gi and Gs was quantified in enriched membrane preparations of thyroid gland tissue, using immunoblotting with Gi and Gs antibodies and toxin-catalyzed ADP-ribosylation.

Results—Expression of Gi was significantly reduced in thyroid gland adenomas from hyperthyroid cats, compared with normal thyroid gland tissue from euthyroid cats. Expression of Gs was similar between the 2 groups.

Conclusions and Clinical Relevance—A decrease in expression of Gi in adenomatous thyroid glands of cats may reduce the negative inhibition of the cAMP cascade in thyroid cells, leading to autonomous growth and hypersecretion of thyroxine. Understanding the molecular mechanisms for hyperthyroidism in cats may lead to better treatment or, ultimately, prevention of the disease. (Am J Vet Res 2000;61:874–879)

Abstract

Objective—To determine whether expression of G proteins (Gi and Gs) is altered in thyroid gland adenomas obtained from hyperthyroid cats.

Sample Population—Adenomatous thyroid glands obtained from 8 hyperthyroid cats and thyroid glands obtained from 4 age-matched euthyroid cats.

Procedure—Expression of Gi and Gs was quantified in enriched membrane preparations of thyroid gland tissue, using immunoblotting with Gi and Gs antibodies and toxin-catalyzed ADP-ribosylation.

Results—Expression of Gi was significantly reduced in thyroid gland adenomas from hyperthyroid cats, compared with normal thyroid gland tissue from euthyroid cats. Expression of Gs was similar between the 2 groups.

Conclusions and Clinical Relevance—A decrease in expression of Gi in adenomatous thyroid glands of cats may reduce the negative inhibition of the cAMP cascade in thyroid cells, leading to autonomous growth and hypersecretion of thyroxine. Understanding the molecular mechanisms for hyperthyroidism in cats may lead to better treatment or, ultimately, prevention of the disease. (Am J Vet Res 2000;61:874–879)