Sex Differences during the Development of Vitamin D Deficiency in the Rat: Serum Parathyroid Hormone, Calcitonin, Calcium, and Phosphorus*

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Abstract
Male and female Holtzman rats were raised from weaning on a vitamin D-deficient diet (−D). Control (+D) animals were raised on the same diet and orally given 70 IU vitamin D3 twice each week. Serum Ca levels fell at the same rate in −D males and females. In contrast, serum parathyroid hormone increased more rapidly in males than females, but reached the same maximal level in both sexes. There were no sex differences in serum Ca or parathyroid hormone in the +D group. Serum calcitonin increased with age in all groups. This increase began at an earlier age in females than in males in both +D and −D animals. In both sexes, the increase occurred several weeks earlier in +D than in -D animals, and within each of these groups, males had higher phosphate levels than females. Female rats exhibited greater longevity on the -D diet than their male counterparts. Results of this study document prominent sex differences in the endocrine regulation of Ca homeostasis that were revealed during the development of vitamin D deficiency in the rat.