THE EFFECT OF HIGH OR LOW DIETARY CALCIUM ON BONE AND CALCIUM HOMEOSTASIS IN YOUNG MALE-RATS

Young male rats (100 g body weight) were fed diets containing varying amounts of calcium. Body weight and bone development were studied toge ther with various endocrine parameters, including blood levels of Ca2, calcitonin, parathyroid hormone, vitamin D, and gastrin, and the ent erochromaffin-like (ECL) cell-related parameters gastric mucosal histi dine decarboxylase activity and histamine concentration. A diet contai ning 0.5% calcium resulted in optimum body weight gain and bone develo pment. A lower calcium intake impaired body weight gain and bone devel opment. The impairment was manifested in reduced bone calcium content whereas the size of the bones was unaffected. The net absorption of ca lcium seemed to be proportional to the calcium intake. A low calcium d iet (0.03%) raised the circulating levels of 1,25(OH)2D and parathyroi d hormone and lowered 25(OH)D3 and Ca2+, whereas a high calcium diet ( 5.46%) raised calcitonin, Ca2+, 25(OH)D3, and 1,25(OH)2D. In addition, the low calcium diet lowered the circulating gastrin concentration an d the histidine decarboxylase activity and histamine content of the EC L cells in the gastric mucosa. A high calcium diet raised the circulat ing gastrin concentration, but the rise was not associated with an inc rease in the histidine decarboxylase activity and histamine content.