CONTRIBUTION OF INTESTINAL CALCIUM ABSORPTION TO 1,25-DIHYDROXYVITAMIN D₃-INDUCED CALCIUM ACTION IN THE TOTAL PARENTERAL NUTRITION RAT

Abstract

To investigate the contribution of intestinal calcium (Ca) absorption to 1,25-dihydroxyvitamin D₃ (1,25(OH) ₂D₃)-induced Ca action, we assessed parameters related to Ca metabolism after a single dosing of 1,25(OH)₂D ₃ in the total parenteral nutrition (TPN) solution or 5% D-mannitol (MAN) solution treatment with rats. Animals were divided into 6 groups (vehicle, 100 μg/kg p.o. and 25 μg/kg i.v.; n=8) in Experiment 1 and 8 groups (vehicle, 1, 10 and 100 μg/kg p.o.; n=6) in Experiment 2 at TPN or MAN solution treatment. In both experiments, the parameters related to Ca metabolisms, urinary Ca and urinary deoxypyridinoline on 0-24 hr or serum Ca, osteocalcin and parathyroid hormone at 24 hr were measured after 1,25(OH)₂D ₃ dosing. 1,25(OH)₂D₃-related increased urinary Ca or serum Ca were observed in both experiments. Decrease rates in change of urinary Ca in TPN solution treatment rats were 36.3% (100 μg/kg p.o.) or 47.1% (25 μg/kg i.v.) of MAN solution treatment rats in Experiment 1, and 29.0% (1 μg/kg), 56.2% (10 μg/kg) or 35.3% (100 μg/kg) of MAN solution treatment rats in Experiment 2. Decrease rates in change of serum Ca at 72 hr in TPN solution treatment rats were 57.3% (100 μg/kg p.o.) or 44.5% (25 μg/kg i.v.) of MAN solution treatment rats in Experiment 1, and were 57.0% (100 μg/kg) of MAN solution treatment rats in Experiment 2. There were no differences in the change of serum Ca in the 1,25(OH)₂D₃ 1 or 10-μg/kg group in Experiment 2. Our results suggest that differences in urinary Ca or serum Ca between MAN solution treatment rats and TPN solution treatment rats express the contribution of intestinal Ca absorption to 1,25(OH)₂D₃-induced Ca action in the conditions of the study.