Changes in Response to Calcitonin Following Prolonged Administration to Intact Rats

Summary

The responses of intact rats to prolonged administration of CT, as measured by different parameters, were of variable duration. CT promoted an increase in body weight and bone mass (humerus) of approximately 1% per week above control values, and this effect was undiminished up to 90 days. Similarly the hypophosphatemic response to CT persisted for 90 days, while the hypocalcemic effect was not observed after 42 days. The decrease in plasma acid phosphatase levels was the most transient effect of CT, which was not obtained beyond 7 days. These findings are consistent with a compensatory hyperparathyroidism. The persistence of the hypophosphatemia and growth-stimulating effect may result from a concerted action of CT and PTH, while the disappearance of hypocalcemia and depression of acid phosphatase activity could be the result of antagonistic effects of the hormones.