摘要：Discriminatory uptake of calcium (Ca) and strontium (Sr) by the intestine that had been shown to become more strict with age was examined to get a more insight into the regulatory mechanisms in rats. Active transports of Ca and Sr at the small intestine (duodenum, proximal and distal jejunum, and ileum) were compared using the everted gut-sac procedure between young and adult rats aged 5 and 25 weeks old, respectively. The ratio of S/M (the ratio of 45Ca and 85Sr transported against the concentration gradient from mucosal to serosal sides) indicated that Ca is transported actively only in young rats, while Sr is transported non-actively at any sites of the intestine examined in both young and adult rats. The discriminatory ability for Ca and Sr at the intestine was compared between the two age groups with the Sr/Ca ratio obtained by the ligated-loop procedure. The ratio was about 1.0 at the duodenum in young rats, while it was shown to be 0.4-0.6 at the other sites in young rats and also at all sites of the intestine in adult rats, indicating that the discriminatory ability is lowered to half at the duodenum in young rats. Phospholipid composition of the duodenum brushborder membrane was compared between young and adult rats to examine the effect of its change on the discriminatory uptake of Ca and Sr. In young rats, phosphatidylcholine increased and phosphatidylethanolamine decreased in composition. These results suggest that changes in phospholipid composition in the duodenum brushborder membrane may explain the change with age in the discriminatory uptake of Ca and Sr at the intestine.
