A lysosomal study of cold-induced hyperthyroidism in the rat: comparison to human hyperthyroid tissue.
Prolonged exposure to cold in the adult rat is considered an acceptable model to study experimental hyperthyroidism. In our experiments adult rats were exposed to cold (1 degree to 4 degrees C) for various periods of time, after which their thyroid tissue and plasma were assayed for lysosomal enzyme activity. In additional animal experiments we examined the cold-exposed rats during propranolol treatment. After 2 weeks of exposure to cold, rat thyroid glands were hypertrophied and hypervascular. There was a significant increase in all three lysosomal enzymes measured in the rat thyroid tissue compared to age-matched controls. The percent of enzyme activity found in the various subcellular fractions did not change. The plasma triiodothyronine concentration increased slightly in the cold-exposed rats, whereas there was no change in thyroxine or lysosomal activity. Propranolol had no effect. In separate experiments human thyroid tissue from patients with diffuse toxic goiter or histologically normal thyroid tissue was examined. Similar to cold-exposed rat thyroid tissue, diffuse toxic goitrous tissue showed a twofold to threefold increase in lysosomal enzyme activity compared to control tissue. These data suggest that increased thyroidal lysosomal enzyme synthesis is one of the factors operative in the increased secretion of active thyroid hormones in Graves' disease.
D000818:Animals; D002402:Cathepsin D; D002403:Cathepsins / Q000378:metabolism; D002553:Cerebroside-Sulfatase / Q000378:metabolism; D003080:Cold Temperature; D004195:Disease Models, Animal; D005966:Glucuronidase / Q000378:metabolism; D006801:Humans; D006980:Hyperthyroidism / Q000201:enzymology* / Q000209:etiology; D008247:Lysosomes / Q000201:enzymology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats
D011433:Propranolol; D002553:Cerebroside-Sulfatase; D005966:Glucuronidase; D002403:Cathepsins; D002402:Cathepsin D