Adaptations in the calcium and phosphorus metabolism of sheep in response to an intravenous infusion of Ca.

1. The effect on calcium and phosphorus metabolism of a high rate of Ca infused directly into the blood of Ca -deficient wethers, already receiving an adequate Ca intake, has been studied by a combination of balance and radioisotope techniques. 2. The rate of Ca retention, which was already high, increased only slightly during the infusion before it reached a maximum. The surplus Ca was compensated for by a decrease in the rate of absorption and an increase in the rate of urinary Ca excretion. 3. These findings support the theory that at maximum retention the rate of Ca absorption becomes regulated according to the rate at which Ca can be stored in bone. 4. results suggest that the decreased absorption was due to a decrease in the rate of active absorption and that the low rate remaining was due to diffusion. 5. The rate of P retention was increased by the Ca infusion, possibly as a result of the increased Ca retention.