Changes Due to Age in the Hypocalcemic and Hypophosphatemic Effects of Salmon Calcitonin in Growing Rats 1

Summary

These studies have compared the hypocalcemic and hypophosphatemic effects of salmon calcitonin (SCT) in male rats between the ages of 37 and 138 days. In addition, the ability of SCT to increase the rate of disappearance of ³²P (injected 1 hr prior to SCT) was also compared for these ages. SCT was administered subcutaneously at a constant dosage of 0.6 MRC mU/g body weight. Previously reported changes in the hypocalcemic effect of porcine thyrocalcitonin (PCT) with age were confirmed by these studies with SCT; namely a decrease in both the depth of the hypocalcemia produced and its duration. In contrast, changes with age in the hypophosphatemic effect of SCT were: (a) a delay in the time after hormone injection at which the maximum hypophosphatemia was produced; and (b) a delay in the time of recovery from the single injection. At all ages, the effect of SCT on plasma ³²P disappearance rates mirrored those on stable phosphate. It is suggested that these studies add further evidence that the hypocalcemia and hypophosphatemia produced by SCT are the reflection of different physiological responses; and that the effect of SCT on phosphate is to produce a rapid movement of this ion from plasma, in contrast to its inhibition of calcium entry into plasma.

Technical supervision of these experiments by Mrs. Dorothy Raneri is acknowledged. Also thanks are given to Mrs. Blanche Holloway for her technical assistance. The advice of Dr. J. J. B. Anderson in the performance of these experiments is appreciated.