Role of vitamin D for calcium (and phosphate) absorption in newborn piglets
1994
Harmeyer, J. (School of Veterinary Medicine, Hannover (Germany). Dept. of Physiology)
Newborn piglets with inherited calcitriol deficiency, which is due to an inborn error of renal conversion of 25OHD to 1,25(OH)2D3, transport calcium actively from the gut into blood. This mechanism disappears when the piglets are three to five weeks old at which age the piglets develop hypocalcemia, hypophosphatemia and rickets. Does early postnatal transport of calcium depend on calcitriol? Our experiments showed that these piglets already lacked renal l-hydroxylase activity at birth so that the circulating concentration of calcitriol in their plasma was only 1/3 that of normal control piglets and remained unchanged up to five to six weeks of age. This concentration was unrelated to the change in active calcium transport of the gut, which occurred at an age of three to five weeks. The binding affinity of the intestinal vitamin D receptor was also not different in piglets early post partum as compared to an age of five to six weeks. This excluded the possibility that calcitriol acted more efficiently on intestinal calcium transport in newborn piglets in the presence of low circulating concentrations of calcitriol. No indications were obtained from the results to suggest that active intestinal calcium transport in newborn piglets is mediated by calcitriol.
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