High Calcium in the Diet and Vitamin D Inhibit a Bone Matrix Degrading Enzyme $\beta$-Glucuronidase Activity

A lysosomal and matrix degrading enzyme $\beta$-glucuronidase activity was measured in BALS/c mice fed high and low Ca in combination with the i.p. adminstration of calcium-regulating hormones including parathyoid hormone(PTH), calcitonin(CT) and cholecalciferol(Vit D). After feeding experimental diets for five weeks, mice were sacrificed by cervical dislocation and the enzyme was fluometrically measured at 440nm. $\beta$-Glucuronidase activity was inhibited by high calcium in the diet. in addition, vitamin D also inhibited the enzyme activity in the serum regardless of the level of dietary calcium. In contrast, PTH has shown to stimulate the enzyme at all the levels of dietary calcium. Calcitonin, and inhibitor of PTH action for bone resorption, revealed to curb PTH effect in this enzyme, whereas CT stimulated the action of vitamin D in the serum. The above results led us to conclude that osteoclastic bone resorption and senile osteoporosis may be reduced by adequate dietary calcium and vitamin D.