Age-related differences in the hypocalcemic effect of calcitonin and calcium excretion in female rats

The effects of aging on the concentration of plasma calcium and urinary calcium excretion in response to human calcitonin (hCT) were investigated in rats. Old (23 months) and young (5 months) female rats were housed individually in metabolic cages. Daily urinary samples were collected over 3 days prior to the hCT injection, and at the 2nd and the 26th hr following the hCT injection. All rats were catheterized via the right jugular vein before a single intravenous injection of hCT (40 ng/kg). Blood samples were collected from the jugular catheter before and after the hCT injection. The basal level of urine flow and calcium excretions were greater in old than in young female rats. The hCT injection significantly decreased the plasma calcium concentration in young female rats, compared to old female rats at 10, 30, and 60 min after the injection. Two hrs after hCT injection, the urinary calcium concentration decreased greater (p less than 0.01) in young than in old female rats. These findings suggest that the reduction of the hypocalcemic and hypocalciuric effects of CT in female rats was age-associated.