Evaluation of experimental methods to induce congenital hypothyroidism in guinea pigs for use in the study of congenital hypothyroidism in horses

Geneviève H. D'Amours Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.
Present address is the Animal Health Unit, Life and Environmental Sciences Animal Resources Centre, Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4.

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Susan M. Taylor Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.

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Ernest D. Olfert Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.
Animal Resources Centre, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.

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Elemir Simko Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.

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Andrew L. Allen Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5B4.

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Abstract

Objective—To develop a method to reliably induce congenital hypothyroidism in guinea pigs (Cavia porcellus) and assess similarities between the resultant developmental abnormalities and those described in horses with congenital hypothyroidism.

Animals—35 female guinea pigs and their offspring.

Procedure—Guinea pigs were allocated to control groups or groups treated with a low-iodine diet before and throughout gestation; an SC injection of 100 or 200 µCi of radioactive iodine 131 (131I) on day 40 of gestation; or 0.1% propylthiouracil (PTU) continuously in the drinking water, beginning day 3 or 40 of gestation. In all groups, assessments included gestation duration, litter size, proportion of stillborn pups, and laboratory analyses in live pups and dams; postmortem examinations were performed on all pups and dams and selected tissues were examined histologically.

Results—Compared with control animals, pups from dams receiving a low-iodine diet or 131I SC had mild changes in their thyroid glands but no grossly or radiographically detectable lesions of hypothyroidism. Pups from dams receiving PTU were often stillborn (24/27 pups) and had enlarged thyroid glands (characterized by large, variably sized follicles of tall columnar epithelium and little or no colloid), an incomplete coat, and radiographically detectable skeletal dysgenesis.

Conclusions and Clinical Relevance—Many of the lesions detected in guinea pig pups from the experimentally treated dams were similar to those described in foals with congenital hypothyroidism. Experimental induction of congenital hypothyroidism in guinea pigs may be useful for the study of naturally occurring congenital hypothyroidism in horses. (Am J Vet Res 2004;65:1251–1258)

Abstract

Objective—To develop a method to reliably induce congenital hypothyroidism in guinea pigs (Cavia porcellus) and assess similarities between the resultant developmental abnormalities and those described in horses with congenital hypothyroidism.

Animals—35 female guinea pigs and their offspring.

Procedure—Guinea pigs were allocated to control groups or groups treated with a low-iodine diet before and throughout gestation; an SC injection of 100 or 200 µCi of radioactive iodine 131 (131I) on day 40 of gestation; or 0.1% propylthiouracil (PTU) continuously in the drinking water, beginning day 3 or 40 of gestation. In all groups, assessments included gestation duration, litter size, proportion of stillborn pups, and laboratory analyses in live pups and dams; postmortem examinations were performed on all pups and dams and selected tissues were examined histologically.

Results—Compared with control animals, pups from dams receiving a low-iodine diet or 131I SC had mild changes in their thyroid glands but no grossly or radiographically detectable lesions of hypothyroidism. Pups from dams receiving PTU were often stillborn (24/27 pups) and had enlarged thyroid glands (characterized by large, variably sized follicles of tall columnar epithelium and little or no colloid), an incomplete coat, and radiographically detectable skeletal dysgenesis.

Conclusions and Clinical Relevance—Many of the lesions detected in guinea pig pups from the experimentally treated dams were similar to those described in foals with congenital hypothyroidism. Experimental induction of congenital hypothyroidism in guinea pigs may be useful for the study of naturally occurring congenital hypothyroidism in horses. (Am J Vet Res 2004;65:1251–1258)

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