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Research Article Free access | 10.1172/JCI109979

Role of Vitamin D Glucosiduronate in Calcium Homeostasis

Sreeramulu Nagubandi, Rajiv Kumar, James M. Londowski, R. A. Corradino, and Pamela S. Tietz

Endocrine Research Unit, Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55901

Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

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Endocrine Research Unit, Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55901

Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

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Endocrine Research Unit, Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55901

Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

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Endocrine Research Unit, Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55901

Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

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Endocrine Research Unit, Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55901

Department of Physical Biology/Section of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

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Published December 1, 1980 - More info

Published in Volume 66, Issue 6 on December 1, 1980
J Clin Invest. 1980;66(6):1274–1280. https://doi.org/10.1172/JCI109979.
© 1980 The American Society for Clinical Investigation
Published December 1, 1980 - Version history
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Abstract

Evidence has been presented suggesting the presence of vitamin D3 3β-glucosiduronate and 1,25-dihydroxyvitamin D3 glucosiduronate in rat bile. To evaluate the role of vitamin D glucosiduronates in calcium and phosphorus homeostasis, we synthesized vitamin D3 3β-glucosiduronate and tested its biological activity in calcium- and vitamin D-deficient rats. After the intravenous administration of vitamin D3 3β-glucosiduronate to rats maintained on a low calcium diet, there was an increase in duodenal calcium transport and an increase in serum calcium. Vitamin D3 3β-glucosiduronate, however, was less active than equimolar amounts of vitamin D3. At doses of less than 0.65-1 nmol per rat, the conjugate exhibited no activity. When vitamin D3 3β-glucosiduronate was administered to vitamin D-deficient rats, 25-hydroxyvitamin D was detected in the serum; the increase in serum 25-hydroxyvitamin D levels was less than that observed after the administration of an equimolar amount of vitamin D3. Vitamin D3 3β-glucosiduronate showed no detectable activity in the induction of calcium binding protein in chick embryonic duodena, a system in which no endogenous steroid β-glucuronidase activity is detectable. These data demonstrate that vitamin D3 3β-glucosiduronate is biologically active in vivo and that the observed activity is due to hydrolysis of the conjugate to vitamin D3. As vitamin D3 3β-glucosiduronate is excreted in the bile of rats, it is possible that this conjugate is reutilized in vivo after hydrolysis to free vitamin D3. These results suggest the existence of a mechanism for reutilization of the biliary products of vitamin D3.

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