Effect of 1,25-dihydroxyvitamin D3 on intestinal calcium absorption in strontium-fed rats. |
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Authors: | H J Armbrecht R H Wasserman M E Bruns |
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Institution: | 1. Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853 U.S.A.;2. Department of Pathology, University of Virginia Medical Center, Charlottesville, Virginia 22901 U.S.A. |
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Abstract: | These studies investigated the initial stimulation of intestinal calcium absorption in the rat by 1,25-dihydroxyvitamin D3. To produce a functional vitamin D3-deficiency, rats were fed a diet containing 2.4% strontium. After 10 days on the diet, intestinal calcium uptake, as measured by everted gut sacs, was significantly depressed. Strontium-fed rats were dosed orally with 1,25-dihydroxyvitamin D3, and changes in intestinal calcium uptake, intestinal alkaline phosphatase activity, and intestinal calcium-binding protein were measured as a function of time after dose. Calcium uptake was significantly increased in the proximal 2.5 cm of the duodenum at 4 h and along the whole duodenum by 7 h. Intestinal alkaline phosphatase activity, measured in a Triton extract of the mucosal homogenate and in isolated brush border complexes, was also increased by 7 h. Using both gel electrophoresis and immunodiffusion against a specific antiserum, an increase in intestinal calcium-binding protein was detected in intestinal supernate at 4 h after dosing. Almost no calcium-binding protein was detectable in strontium-fed rats dosed with propylene glycol only. These time studies are consistent with a role for both alkaline phosphatase and calcium-binding protein in the 1,25-dihydroxyvitamin D3-stimulated uptake of calcium by the intestine. In addition, the usefulness of strontium feeding for producing a functional vitamin D3 deficiency in rats is demonstrated. |
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