Endocrinology, Vol 124, 565-572, Copyright © 1989 by Endocrine Society

ARTICLES

Bone mineral homeostasis in spontaneously diabetic BB rats. I. Abnormal vitamin D metabolism and impaired active intestinal calcium absorption

BL Nyomba, J Verhaeghe, M Thomasset, W Lissens and R Bouillon
Department of Obstetrics and Gynecology, Katholieke Universiteit Leuven, Belgium.

Calcium homeostasis was investigated in male BB rats with a diabetes duration of 3-4 weeks and compared with that in nondiabetic littermates either fed ad libitum or receiving selective semistarvation or an oral Ca supplement to obtain additional weight-matched and Ca intake-matched control groups. Diabetic rats had markedly increased food and Ca intake, so that their net Ca balance remained positive despite a 13- fold increase in urinary Ca excretion and a disappearance of active duodenal Ca absorption. Decreased duodenal Ca uptake correlated with decreased 1,25-(OH)2D3 levels (89 +/- 15 vs. 160 +/- 13 pg/ml in nondiabetic rats), decreased duodenal 9K Ca-binding protein concentrations (10 +/- 1 vs. 21 +/- 2 micrograms/mg protein), and decreased number of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-binding sites in duodenum, although the binding affinity was above normal. Nondiabetic Ca-supplemented rats exhibited a similar response: decreased 1,25-(OH)2D3 (95 +/- 8 pg/ml) and 9K Ca-binding protein (7 +/- 0.5 micrograms/mg protein) concentrations, decreased active duodenal Ca uptake, increased urinary Ca excretion, and a normal net Ca balance. Plasma vitamin D-binding protein levels were decreased by 62% in diabetic rats, due to a marked decrease in production rate, while the plasma half-time remained normal. The free 1,25-(OH)2D3 index was highest in diabetic rats, suggesting partial vitamin D resistance at the duodenal level. In semistarved rats, 1,25-(OH)2D3 levels and active Ca uptake remained normal, and the free 1,25-(OH)2D3 index was increased, together with suppressed vitamin D-binding protein levels. These studies indicate that nutritional abnormalities may contribute to but cannot totally explain the disturbances in vitamin D metabolism, transport, or action at the intestinal level.

This article has been cited by other articles:

				L. L. Lipscombe, S. A. Jamal, G. L. Booth, and G. A. Hawker The Risk of Hip Fractures in Older Individuals With Diabetes: A population-based study Diabetes Care, April 1, 2007; 30(4): 835 - 841. [Abstract] [Full Text] [PDF]

				M. Inaba, H. Morii, T. Katsumata, H. Goto, E. Ishimura, T. Kawagishi, M. Kamao, T. Okano, and Y. Nishizawa Hyperparathyroidism Is Augmented by Ovariectomy in Nagase Analbuminemic Rats J. Nutr., June 1, 2000; 130(6): 1543 - 1547. [Abstract] [Full Text]