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 (45)Ca, (47)Ca and (85)Sr.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 (45)Ca 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.