A Transient Increase in Renal Clearance of Phosphate in Response to Continuous Infusion of Salmon Calcitonin in Rats

The effects of intravenous carrier-free salmon calcitonin on renal clearances of phosphate, calcium, magnesium, sodium and potassium were studied in male parathyroidectomized (PTX) and intact rats. Both natural and synthetic hormone, when infused at constant rates (0.005-0.5 MRC U/hr), produced a rapid increase (peaking at about 60-90min) in phosphate clearance. However, the maximal increase was transient in nature in PTX rats. In intact rats, the phosphaturic response was somewhat more pronounced and the decline after the peak was rather modest. When a large amount (4 MRC U) of calcitonin was given in divided doses, the second dose produced a lesser extent of phosphaturia in both intact and PTX rats. The phosphaturic response was accompanied by an increase in sodium and potassium clearances in PTX rats and by an increase in potassium clearance in intact rats. A fall in the apparent clearance values for calcium and magnesium occurred and was maintained throughout the infusion period of hormone in both intact and PTX rats In conclusion, PTX rats respond to the intravenous administration of salmon calcitonin with a transient phosphaturic response which is accompanied by parallel diuresis of sodium and potassium along with sustained retention of calcium and magnesium by the kidney.