Abstract
Calcium transport in the proximal duodenum was measured in male rats of various ages by the everted intestinal sac method. Calcium transport markedly and progressively diminished from 54 days to 384 days of age despite adequate intakes of vitamin D 3 (10 IU/day). Additionally, feeding low phosphorus and/or low calcium diets for 24 days did not result in an enhanced calcium transport in old (1 year) rats while showing the expected enhancement in young rats (24 days). The administration of 325 pmoles of either 1,25-dihydroxyvitamin D 3 or 1α-hydroxyvitamin D 3 daily increased intestinal calcium transport in both young and old rats. This response was accompanied by increased serum calcium in young rats and increased serum phosphorus in old rats. Administration of vitamin [1,2 3H]D 3 daily (10 IU) for 6 days orally and chromatography of the extracts of serum and intestine permitted the demonstration that the diminished calcium transport with age is positively correlated with diminished levels of 1,25-dihydroxy-[1,2 3H] D 3 in serum and intestinal mucosa. It appears that the decreased intestinal absorption with age is a result of a diminished formation of 1,25-dihydroxyvitamin D 3. The inability of aged rates to alter this condition under dietary depletion of calcium and/or phosphorus may play a significant role in the development of bone disease in the aged.
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