Effect of thyroid hormone on the vitamin D metabolism and bone pathology of adult female wistar rats

Abstract

1. 1. Groups of young and mature female Wistar rats were made thyrotoxic by subcutaneous injections of T 4 or T 3. Plasma and femurs were analysed for chemical parameters as indices of altered bone pathology. 2. 2. Thyrotoxic animals showed a significant decrease in the level of albumin in plasma and an increase in alkaline phosphatase. Electrophoresis of alkaline phosphatase suggested an increase in bone type isoenzyme. 3. 3. Young and mature rats treated with T 3 showed changes in bone analysis with a significant rise in the water content and a decrease in calcium. 4. 4. Young thyrotoxic rats had the same plasma 25-hydroxyvitamin D (25[OH]D) as controls and there was no change in the in vivo conversion of vitamin D to 25(OH)D. However, mature rats treated with T 3 had a slightly but significantly lower in vivo conversion of 25(OH)D to more polar derivatives. 5. 5. These results give little support to the suggestions that thyroid induced changes in bone are due to a direct effect on vitamin D metabolism.