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

This article discusses the establishment of a method to induce congenital hypothyroidism in guinea pigs, entailing different experimental conditions. It aims to evaluate the similarity of induced developmental abnormalities to those found in horses with natural congenital hypothyroidism.

Methodology

The researchers used 35 female guinea pigs and their offspring for the study. They divided these guinea pigs into control and test groups, where the test groups were subjected to the following treatments:

• Low-iodine diet before and during gestation period
• Subcutaneous injection of 100 or 200 microcurie (radioactivity unit) of radioactive iodine 131, on the 40th day of gestation
• Continuous supply of 0.1% propylthiouracil (PTU), an antithyroid drug, in drinking water, starting from either the 3rd or the 40th day of gestation

These methods were evaluated based on certain parameters such as gestation duration, litter size, proportion of stillborn pups etc. Postmortem examinations were performed and selected tissues were examined histologically (microscopic anatomy).

Results

Among the experimentation groups, it was observed that:

• Pups from dams receiving low-iodine diet or radioactive iodine injection showed mild thyroid gland changes, but no grossly or radiographically noticeable lesions of hypothyroidism were observed.
• Pups from dams receiving PTU were often stillborn, had enlarged thyroid glands characterized by variably sized follicles and incomplete coats. They also displayed skeletal dysgenesis that could be detected using radiography.

Conclusion

The findings indicate potential similarities between the induced developmental abnormalities in guinea pigs and the natural occurrences in horses with congenital hypothyroidism. Thus, the methods developed for inducing congenital hypothyroidism in guinea pigs may prove to be useful in the study of naturally occurring congenital hypothyroidism in horses.