High
calcium leads to the secretion of
calcitonin, and the administration of
1,25-dihydroxyvitamin D3 leads to a decreased transcription of the
calcitonin gene. We now report the effect of chronic
hypercalcemia,
hypocalcemia, and
vitamin D deficiency on
calcitonin gene expression in vivo in the rat.
Hypercalcemia was created by
calcium infusions for 6 h, a high-
calcium diet given to weanling rats for 3 weeks, and the
transplantation of the
Walker carcinosarcoma 256 cell line. Despite serum
calcium as high as 22 mg/dl, there was no difference in
calcitonin mRNA levels among these rats. The control genes studied, actin and
somatostatin, which is specific for C cells in the thyroparathyroid tissue, also did not differ among the different groups of rats. Injected 1,25-(OH)2D3 decreased
calcitonin mRNA levels at 6 h, as previously reported.
Hypocalcemia, created by feeding diets deficient in
calcium and
vitamin D to weanling rats for 3 weeks, had no effect on
calcitonin mRNA levels, in contrast to the large increases in PTH
mRNA levels. These results demonstrate that
calcitonin gene expression in vivo in the rat is regulated by administered 1,25-(OH)2D3 but not by changes in serum
calcium.