Electron-microscopic evaluation of the effect of 1,25-Dihydroxyvitamin D3 and Zinc on tibial metaphyses of growing rats

Bone modeling and skeletal consolidation probably result from a complex sequence of hormonal changes in interaction with nutritionai factors. Peak bone mass, about half of which is accumulated during the adolescent growth spurt, determines the risk of osteoporosis and associated fractures in later life. 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the biologically active hormonal metabolite of vitamin D, is to effect calcium and phosphate homeostasis to ensure the deposition of bone mineral via its regulating intestinal calcium and phosphate absorption. The presence of 1,25(OH)2D3 receptor (VDR) in certain bone cells such as osteoblasts and osteocytes suggests that 1,25(OH)2D3 may elicit a direct stimulatory effect on bone formation. On the other hand, zinc, an essential trace element, plays an important role in bone formation and mineralization. Specially, the gene sequence for VDR was determined and shown to have two zinc fingers at the site of interaction with DNA. Zinc supplementation was reported to be able to enhance the effects of 1,25(OH)2D3 on bone in tissue culture. To clarify the effects of 1,25(OH)2D3 and zinc on bone in vivo, twenty-four 5-week-old male Wistar rats were devided into 4 groups randomly as follows：control group was fed on a standard diet and orally administered olive oil 3 times each week; the experimental groups were fed on 50%-low-zinc diet (Zn-VD+group), standard diet (VD+group) and 150%-high-zinc diet (Zn+VD+group) respectively, and orally administered 10ng/100g body weight lα-OH-D3 3 times each week, which was dissolved in olive oil. 1α-OH-D3 is a synthetic analogue, which seems to be rapidly converted to 1,25(OH)2D3 in vivo. After 4 weeks of feeding, the rats were sacrificed and their tibias were removed. The experimental range was from childhood to ebrly adulthood of rats. Specimens of tibial metaphyses were prepared and then observed by electron microscopy. 1. Scanning electron microscopy (SEM) findings：Compared with the control group, the VD+group showed more collagen fibers and fewer calcareous microdepositions on the surface of bone matrix. There were no obviously different SEM findings observed between the Zn+VD+ group and the VD+group when compared with the control group, except that calcareous microdepositions were more often seen in the Zn+VD+group than those in the VD+group. In the Zn-VD+group, collagen fibers were irregularly-alignmented and calcareous microdepositions were less frequently seen than those in any other