The role of vitamin D metabolites in hypercalcemia of Zucker fa/fa rats.

In order to investigate mineral and vitamin D metabolism in obese rats with hyperinsulinemia, plasma calcium and vitamin D metabolites were measured in Zucker fa/fa rats. Body weight, plasma insulin, and calcium in fa/fa rats were significantly increased compared to their lean littermates (p less than 0.01). However, no significant difference in plasma 25-hydroxyvitamin D (25(OH)D), 24,25-dihydroxyvitamin D, 1,25-dihydroxyvitamin D (1,25(OH)2D) or the ratio of 1,25(OH)2D to 25(OH)D was observed between fa/fa rats and their lean littermates. The hypercalcemia in the rats with hyperinsulinemia, therefore, might be caused by other calcium-regulating hormones or some factors other than 1,25(OH)2D. In addition, the hyperinsulinemia associated with obesity may not produce the accelerated conversion from 25(OH)D into 1,25(OH)2D.