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recent study 14 compared echocardiographic examinations of hyperthyroid and euthyroid cats and revealed differences in right-heart and pulmonary arterial hemodynamics, with no evidence of PH. Notably, this was a retrospective study, with the limitation
In cats, hyperthyroidism is most commonly caused by autonomously functioning thyroid gland adenomas 1–3 and is clinically and histologically similar to toxic nodular goiter in humans. 1 In elderly humans, a mild to moderate lifetime deficiency
,20,33–38 In veterinary medicine, it has been used in lameness evaluations to detect ligamentous, osseous, muscular, articular, and neurologic injuries in horses, cats, dogs, and raccoons. 3,4,18,19,39–43 Hyperthyroidism is a multisystemic disease defined as
Hyperthyroidism is the most common endocrinopathy in cats, and it affects a large percentage of middle-aged to older animals. Since its recognition as a clinical entity approximately 30 years ago, it has been diagnosed with increasing frequency
Various methods for treating cats with hyperthyroidism have been described, 1,2 with the most common medical treatments involving administration of methimazole or radioactive iodine. Although several reports on the effects of treatment of
some forms of vasculitis, myeloperoxidase-specific ANCAs result in various combinations of rapidly progressive glomerular and pulmonary diseases. Anti-neutrophil cytoplasmic autoantibodies also develop in a subset of humans with hyperthyroidism. These
Abstract
Objective—To determine whether the increasing prevalence of feline hyperthyroidism is the result of aging of the cat population and whether consumption of canned foods at various times throughout life is associated with increased risk of hyperthyroidism.
Design—Retrospective and case-control studies.
Study Population—Medical records of 169,576 cats, including 3,570 cats with hyperthyroidism, evaluated at 9 veterinary school hospitals during a 20-year period, and 109 cats with hyperthyroidism (cases) and 173 cats without hyperthyroidism (controls).
Procedure—Age-adjusted hospital prevalence of hyperthyroidism was calculated by use of Veterinary Medical Database records. On the basis of owners' questionnaire responses, logistic regression was used to evaluate associations between consumption of canned food and development of hyperthyroidism.
Results—Age-specific hospital prevalence of feline hyperthyroidism increased significantly from 1978 to 1997. Overall, consumption of pop-top canned (vs dry) food at various times throughout life and each additional year of age were associated with greater risk of developing hyperthyroidism. In female cats, increased risk was associated with consumption of food packaged in pop-top cans or in combinations of pop-top and non-pop-top cans. In male cats, increased risk was associated with consumption of food packaged in pop-top cans and age.
Conclusions and Clinical Relevance—These findings suggest that the increasing prevalence of feline hyperthyroidism is not solely the result of aging of the cat population and that canned foods may play a role. (J Am Vet Med Assoc 2004;224:879–886)
Abstract
Objective—To identify within guanosine triphosphate–binding proteins (G proteins) the subset of inhibitory G proteins (Gi) that have decreased expression in adenomatous thyroid glands obtained from hyperthyroid cats.
Sample Population—Adenomatous thyroid glands obtained from 5 hyperthyroid cats and normal thyroid glands obtained from 3 age-matched euthyroid cats.
Procedure—Expression of Gi1, Gi2, and Gi3 in enriched membrane preparations from thyroid glands was quantified by use of immunoblotting with Gi subtype-specific antibodies.
Results—Expression of Gi2 was significantly decreased in tissues of hyperthyroid glands, compared with expression in normal thyroid tissue. Expression of Gi1 and Gi3 was not significantly different between normal thyroid tissues and tissues from hyperthyroid glands.
Conclusions and Clinical Relevance—A decrease in Gi2 expression decreases inhibition of adenylyl cyclase and allows a relative increase in stimulatory G protein expression. This results in increased amounts of cAMP and subsequent unregulated mitogenesis and hormone production in hyperthyroid cells. Decreased Gi2 expression may explain excessive growth and function of the thyroid gland in cats with hyperthyroidism. (Am J Vet Res 2005;66:1478–1482)
Abstract
Objective—To identify dietary and environmental risk factors for hyperthyroidism in cats.
Design—Case-control study.
Animals—100 cats with hyperthyroidism and 163 control cats.
Procedure—Medical records were examined, and owners completed a mailed questionnaire. Data collected included information regarding demographic variables, environmental exposures, and diet, including preferred flavors of canned cat food.
Results—Case cats were significantly less likely to have been born recently than control cats. Housing; exposure to fertilizers, herbicides, or plant pesticides; regular use of flea products; and presence of a smoker in the home were not significantly associated with an increased risk of disease, but cats that preferred fish or liver and giblets flavors of canned cat food had an increased risk.
Conclusions and Clinical Relevance—Results suggest that cats that prefer to eat certain flavors of canned cat food may have a significantly increased risk of hyperthyroidism. (J Am Vet Med Assoc 2000; 217:853–856)
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)
