Differential effects of 1,25-dihydroxyvitamin D 3 upon intestinal vitamin D 3-dependent calbindin (a 28,000-dalton calcium binding protein) and its mRNA in D-replete and D-deficient chickens

Abstract

The effect of vitamin D 3 status upon the responsiveness of chick intestinal epithelium to exogenous 1,25-dihydroxyvitamin D 3 [1,25(OH) 2D 3]was studied. Intestinal calbindin [A recent consensus decision was made to redesignate the vitamin D-dependent calcium binding protein as “calbindin-D 28K” ( R. H. Wasserman (1985) in Vitamin D: Chemical, Biochemical, and Clinical Update (Norman, A. W., Schaefer, K., Grigoleit, H.-G., and Herrath, D. V., Eds.), pp. 321–322, de Gruyter, Berlin/New York) .]protein and intestinal calbindin mRNA were quantitated in birds which had been raised on a vitamin D 3-deplete (−D) or on a vitamin D 3-replete (+D) diet. 1,25(OH) 2D 3 stimulated intestinal calbindin mRNA levels in −D chickens in a proportional dose-dependent manner, when measured at both 12 and 48 h after administration of the hormone. A first increase was observed with 1,25(OH) 2D 3 concentrations between 0.065 and 0.65 nmol. The maximal stimulation achieved by 1,25(OH) 2D 3 (6.5–18 nmol) in−D tissue was approximately 10-fold over the calbindin mRNA levels present in vehicle-treated birds. The increase of calbindin mRNA in −D birds was associated with a similar dose-dependent increase in calbindin protein in 1,25(OH) 2D 3-treated −D birds after 12 or 48 h. In +D intestine, while exogenous 1,25(OH) 2D 3 also increased calbindin mRNA levels in a dose-dependent fashion, the maximal stimulation observed after 5 h (1.2- to 2-fold) was clearly less than that observed in −D intestine. In contrast to −D birds, intestinal calbindin levels in +D birds were decreased by administration of exogenous 1,25(OH) 2D 3. Administration of 32.5 to 65 nmol 1,25(OH) 2D 3 resulted in an approximately 1.8-fold repression compared to vehicle-treated birds. This differential responsiveness between +D and −D intestines with respect to 1,25(OH) 2D 3 was not explained either by differences in the uptake in the chromatin fractions of these tissues or by metabolism of radiolabeled 1,25(OH) 2D 3. Dietary withdrawal of vitamin D 3 led to a gradual decline in ambient intestinal calbindin levels, while intestinal sensitivity to 1,25(OH) 2D 3 was restored. These findings suggest that vitamin D 3 status regulates intestinal responsiveness to the seco-steroid 1,25(OH) 2D 3.