In vivo Intestinal Transport of Calcium and Water from Solutions Recycled through Healed Gut Loops in Dogs

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Abstract
An in vivo study was made of the dynamic changes of Ca, and water concentrations in solutions recycled through healed jejunal gut loops of healthy adult dogs. When the solution contained no Ca, Ca moved into the gut lumen regardless of the osmolarity of the initial solution, until the calcium concentration in the lumen reached 2 to 3 mEq/liter. Above this concentration Ca was absorbed. The rate of Ca absorption increased with increasing Ca concentrations in the lumen. Net Ca absorption was inversely proportional to the average rate of water absorption. Because water was absorbed more rapidly than Ca, the concentration of the latter always rose with an increasing rate throughout the course of the experiment. Hypotonicity caused slight, if any, change in Ca or water absorption rates. Hypertonicity altered water absorption markedly; there was a movement of water into the lumen until the osmolarity of the contents approached 385 ± 12 milliosmoles/liter. During this interval of 2.2 ± 0.2 hours Ca absorption was significantly slowed. In all instances, when osmotic equilibrium had been obtained, Ca and water absorption proceeded at the usual rates. These studies suggested that under physiological conditions, net Ca transfer is in one direction — from gut lumen to blood.