Mechanism of the phosphaturic action of acute intravenous injection of parathyroid extract in the dog

¹ Department of Pharmacology, University of British Columbia, Vancouver, Canada

In the fasted dog, the acute intravenous injection of parathyroid extract leads to an appreciable augmentation of the urinary excretion of endogenous phosphate only when the renal threshold for phosphate excretion is initially low and only when this procedure is accompanied by a corresponding elevation of the filtered phosphate load. In similar circumstances an increase in the glomerular filtration rate by means of abrupt expansion of the extracellular fluid also elicits phosphaturia. These phosphaturic responses may dwindle in spite of persistent elevation of the filtered phosphate load, the rising threshold for phosphate excretion being associated with apparent cellular phosphate depletion. In the parathyroidectomized dog, the acute intravenous injection of parathyroid extract is followed by a considerable transfer of phosphate out of the extracellular fluid compartment, whether or not a concomitant phosphaturia develops.