Alteration in bone metabolism with increasing age: effects of zinc and vitamin D3 in aged rats.

The alteration in bone metabolism with increasing age was investigated in the femoral diaphysis of male rats. Calcium content was highest in the bone from 3-week-old rats (491 +/- 13 mg/g bone ash), falling gradually with aged to 357 +/- 7 and 306 +/- 9 mg/g bone ash in 28- and 52-week-old rats, respectively. Bone zinc content increased until rats were 3 weeks of age, and thereafter remained constant. Deoxyribonucleic acid (DNA) content was highest in the bone from 1-week-old rats, and it decreased markedly with increasing age. Alkaline phosphatase and acid phosphatase activities increased up to 3 weeks, then subsequently declined with age. Thus, the retardation of bone metabolism was induced by ageing. When zinc sulfate (5.0, 10.0 and 20.0 mg Zn/kg body weight) was administered orally for 3 d to 28-week-old rats, alkaline phosphatase activity and calcium content in the femoral diaphysis was elevated markedly by all doses. The oral administration of vitamin D3 (2.0 and 20 micrograms/kg) for 3 d in 28-week-old rats did not produce an appreciable increase in bone alkaline phosphatase activity or calcium content, while 1,25-dihydroxyvitamin D3 (1.5 micrograms/kg) caused a significant increase in those biochemical indices. These results indicate that zinc and 1,25-dihydroxyvitamin D3 play a role as activators in bone metabolism of ageing rats.