AJP - Endocrinology and Metabolism, Vol 258, Issue 2 E377-E381, Copyright © 1990 by American Physiological Society
Elevated 1,25-dihydroxyvitamin D3 and intestinal calbindin-D9k in the toothless rat
M. F. Seifert, R. W. Gray and M. E. Bruns
Department of Anatomy, University of South Dakota School of Medicine, Vermillion 57069.
The toothless (tl) rat is a nonlethal osteopetrotic mutation characterized
by systemic skeletal sclerosis, growth plate morphology suggestive of
rickets, and morphological evidence of reduced osteoclastic bone
resorption. Vitamin D metabolites, serum calcium and phosphorus levels, and
the developmental appearance of vitamin D-dependent intestinal calcium
binding protein (calbindin-D9k) was studied in normal and mutant rats of tl
stock from 7 to 35 days of age. 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] was
found to be significantly elevated in mutant animals by 7 days of age (71
+/- 9 pM, tl/tl vs. 24 +/- 8 pM, +/?) and continued to increase to a peak
of 428 pM at the time of weaning. This was 240% higher than normals at this
period. The elevated levels of 1,25-(OH)2D3 stimulated a significant and
precocious appearance of intestinal calbindin-D9k in mutants, beginning by
14 days of age and reaching their peak levels at 21 days postpartum (25.6
+/- 1.7 micrograms/mg protein, tl/tl vs. 16.4 +/- 1.5 micrograms/mg
protein, +/?). The cause of the elevated circulating levels of 1,25-(OH)2D3
in tl rats is unknown but may be due to the low serum phosphorus levels
present in these animals.
