Renal effects of porcine thyrocalcitonin (TCT) were evaluated in the dog. TCT (8 MRC U/kg/day) was given intramuscularly for 14 days to 7 control dogs and to 10 dogs that had been thyroparathyroidectomized. Renal clearance of phosphorus was measured from the third tothe sixth hr after TCT administration, corresponding to the period of peak biologic activity of TCT as judged from the decrease in serum calcium concentration. In the intact dogs, tubular reabsorption of phosphorus (TRP) decreased significantly during treatment with TCT, and returned toward normal after treatment was stopped. In the thyroparathyroidectomized dogs, TRP did not change appreciably with treatment. In separate studies in thyroparathyroidectomized dogs, TRP did not change significantly during the first 2 hr after the administration of TCT. It is concluded (a) that TCT does not directly influence the renal tubular transport of phosphorus, and (b) that, in the presenceof intact parathyroid glands, TCT increases urinary excretion of P probably through indirect stimulation of parathyroid secretion.
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