THE EFFECT OF DIETARY VITAMIN-D METABOLITES AND ZINC ON NORMAL AND ECTOPIC BONE-FORMATION IN WEANLING RATS

The effect of dietary supplementation of rats with vitamin D metabolites and zinc was examined in selected bones and a short-term in vivo implant model. A 2x2x3 factorial design was utilized with two vitamin D metabolites (cholecalciferol-D3 or 1,25-dihydroxycholecalciferol-1,25(OH)2D3); two levels of dietary zinc (marginal-4.5, and adequate-10 ug/)g diet; and three time periods (11, 14 and 21 days after implantation). Seventy-two female weanling Long-Evans rats were fed their respective diets for three weeks before subcutaneous implantation with demineralized bone powder. The animals were injected intraperitoneally with Ca-45 (0.5uCi/g body weight) 14 h before sacrificing. The ectopic bone implants as well as the femurs, tibias, humeri, scapulas and mandibles were obtained 11, 14 and 21 days following implantation. Implants were fixed, sectioned and stained with toluidine blue The specific bones and the implants were analyzed for calcium, zinc and Ca-45. There was higher calcium concentration in the femurs of animals fed D3 compared to 1,25(OH)2D3. Activities of enzymes (alkaline phosphatase-marker for formation, and acid phosphatase-marker for resorption) were quantitated in the implants. Enzyme activities, mineral deposition and presence of osteoblasts and osteoclasts all provided definitive evidence that the implant system was mimicking the typical dynamic processes normally occurring in bone tissues. An interaction between the form of vitamin D (D3 VS 1,25(OH)2D3) and level of zinc fed to the rats was demonstrated in the implants; calcium and zinc concentrations were higher in the implants of rats fed D3 and adequate zinc than rats fed 1,25(OH)2D3 and adequate zinc. In summary, adequate dietary zinc concentration modulates the effects of vitamin D metabolites; also D3 form has a greater anabolic effect on integrity of the bone than 1,25(OH)2D3. Furthermore, femur appears to be more sensitive than the other bones tested to changes in calcium concentration due to the two forms of vitamin D.