Regulation of plasma calcium and phosphate in calcitonin-infused rats

The effects of long-term constant infusion of moderate doses (2-32 ng/h) of salmon calcitonin (sCT) on plasma Ca (and its radionuclide super(45)Ca), P sub(i), Mg, and on endogenous rat CT (rCT) metabolism were investigated in the rat. Daily variations were included. The results are consistent with a transitory loss of the daily variations for Ca and P sub(i) (day 7) and the later (day 14) spontaneous recovery of some variations in these parameters, although the individuals remain unsynchronized. We suggest that rCT acts, through its own circadian variation, as an internal synchronizer for some circadian functions(s) of Ca metabolism under physiological conditions and that this role is suppressed in the sCT-infused animal.