AJP - Endocrinology and Metabolism, Vol 265, Issue 2 E215-E223, Copyright © 1993 by American Physiological Society
Increased clearance of 1,25(OH)2D3 and tissue-specific responsiveness to 1,25(OH)2D3 in diabetic rats
J. Verhaeghe, A. M. Suiker, R. Van Bree, E. Van Herck, I. Jans, W. J. Visser, M. Thomasset, K. Allewaert and R. Bouillon
Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, Belgium.
The kinetics of 1,25-dihydroxyvitamin D3 [1,25(OH)2-D3] and the in vivo
response to 1,25(OH)2D3 (7.5, 15, and 30 ng/100 g body wt), infused or
injected subcutaneously for 12-14 days, were studied in male spontaneously
diabetic and control BB rats. In control rats, increasing doses of
1,25(OH)2D3 produced parallel increases in plasma 1,25(OH)2D3 and calcium,
urinary calcium, duodenal CaBP9K, and renal CaBP28K. 1,25-(OH)2D3 at 30
ng/100 g markedly raised plasma osteocalcin and osteoblast/osteoid surfaces
in the tibial metaphysis, but inhibited bone mineralization rate. In
diabetic rats, plasma 1,25-(OH)2D3 concentrations were decreased, and the
rise of plasma 1,25(OH)2D3 during 1,25(OH)2D3 infusion was blunted, but the
free 1,25(OH)2D3 index remained normal or above normal. Diabetic rats had
an increased metabolic clearance rate of 1,25-(OH)2D3 (0.38 +/- 0.015 vs.
0.24 +/- 0.007 ml.min-1.kg-1), with no further increase in
1,25(OH)2D3-infused diabetic rats; their relative production rate of
1,25(OH)2D3 was unchanged. The responses of plasma and urinary calcium,
duodenal CaBP9K, and renal CaBP28K to infused 1,25(OH)2D3 were normal, as
was duodenal calcium absorption in 1,25(OH)2D3-injected diabetic rats.
However, the virtual absence of osteoblasts/osteoid in trabecular bone was
unaltered in diabetic rats infused with 30 ng/100 g 1,25(OH)2D3, with only
minimal increase of their low plasma osteocalcin levels. 1,25(OH)2D3
treatment therefore cannot be expected to reverse diabetic osteopenia.
