Stimulation of renal magnesium reabsorption by calcitonin in the rat

The effect of salmon synthetic calcitonin (CT) on the renal excretion of water and electrolytes was investigated in thyroparathyroidectomized (TPTX) nondiuretic rats. CT did not significantly alter the excretion of either H2O, Na, Ca, phosphate (P), or K, but consistently decreased both fractional and absolute excretion rates of Mg. This latter effect was probably the result of enhanced reabsorption by the loop of Henle. The excretion rates of P and K were either increased or decreased by CT administration; the Mg response on both the whole kidney and loop of Henle was always observed, however, irrespective of the P and K response. In other experiments, the decrease in Mg excretion was still observed when the fall in the filtered load of P and Ca secondary to CT administration was prevented by an appropriate infusion of Ca and P. It is concluded that 1) CT can alter K and P excretion rates but this influence can be prevented by maintaining the filtered load of Ca and P constant, and 2) CT exerts a marked stimulatory effect on Mg reabsorption, presumably by enhancing reabsorption by the thick ascending limb.