Calcium metabolism in normal and thyro-parathyroidectomized goats.

1. The effects of thyro-parathyroidectomy on calcium metabolism in the goat have been investigated using stable calcium balance techniques and the isotopes 45Ca, 47Ca and 85Sr. 2. Thyro-parathyroidectomized goats, whether receiving supplementary thyroxine or not, are in negative calcium balance, whereas normal or thyroidectomized animals are in positive balance. 3. Gastro-intestinal absorption of 45Ca is less in thyro-parathyroidectomized goats, whether receiving supplementary thyroxine or not, than in either normal goats or thyroidectomized goats receiving thyroxine supplements. 4. The rate of endogenous secretion of calcium into the gastro-intestinal tract is unchanged by either thyroidectomy or thyro-parathyroidectomy. Urinary excretion of calcium is also apparently unchanged. 5. The bone calcium accretion rate is reduced to approximately the same extent in thyroidectomized and thyro-parathyroidectomized goats. Thyroxine supplements restore the bone accretion rate of both groups of animals to normal or greater than normal levels. 6. The bone calcium resorption rate is greater in thyro-parathyroidectomized goats, whether receiving thyroxine supplements or not, than in either normal goats or thyroidectomized goats receiving thyroxine supplements.