THE ROLE OF VITAMIN-D IN CHORIOALLANTOIC MEMBRANE CALCIUM-TRANSPORT

1,25-Dihydroxyvitamin D-3 (1,25-(OH)(2)D-3) is essential for tt!e transport of eggshell calcium to the embryo across the chorioallantoic membrane (CAM). CAM contains the vitamin D receptor that increases following 1,25-(OH)(2)D-3 injection into embryos at day 10 of incubation. Further, a single injection of 100 ng of 1,25-(OH)(2)D-3 into vitamin D-deficient quail eggs at day 10 of incubation resulted in a significant increase in both body and yolk calcium. This is accompanied by an increase in carbonic anhydrase from low levels in deficiency to normal levels. Acetazolamide (AZ). a specific carbonic anhydrase inhibitor injected into the quail embryos, caused hypocalcemia and hyperphosphatemia. This is similar to the hypocalcemia and hyperphosphatemia found in vitamin D-deficient embryos. These results suggest that one mechanism of action of vitamin D in the mobilization of eggshell calcium is the activation of carbonic anhydrase that acidifies the calcium carbonate shell.