Vitamin D deficiency in rats with normal serum calcium concentrations.

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Abstract
Rats were raised after weaning on a vitamin D-deficient diet which used whole wheat and casein as the major protein source. For at least the 1st year of life, plasma Ca concentrations of these rats were the same as those of vitamin D-replete rats and the rate of growth was normal for at least 6 mo. The following evidence establishes the vitamin D deficiency of the rats (both male and female) on this diet: plasma levels of 1,25-dihydroxycholecalciferol (1,25-dihydroxyvitamin D3) became undetectable after 6 wk on the diet; by 4 mo. of age, the epiphyseal growth plates of the tibia were significantly enlarged and disorganized; when subjected to fracture in a dynamic torsion machine, the femur showed marked weakening as indicated by stress analysis; and isolated kidney cells from the deficient rats showed a 3-fold increase in 25-hydroxyvitamin D 1-hydroxylase activity. When mother rats were placed on the vitamin D-deficient diet during lactation, plasma Ca values in the pups decreased and remained low throughout life and there was a stunted body growth pattern. Hypocalcemia is evidently not a necessary manifestation of vitamin D deficiency; the onset of vitamin D deficiency during neonatal life apparently influences the Ca homeostatic system and the normocalcemic, vitamin D-deficient animal evidently provides an experimental model in which the effects of vitamin D deficiency can be studied independently of hypocalcemia.