THE EFFECT OF PARATHYROID EXTRACT ON RENAL TUBULAR CALCIUM REABSORPTION IN THE DOG*

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Abstract
Filtered calcium and sodium excretion were carefully controlled. In eight of nine clearance experiments, calcium excretion during administration of parathyroid extract decreased significantly despite increased or unchanged filtered calcium and sodium excretion. Increased filtered calcium resulted from increased plasma calcium concentration, increased glomerular filtration rate, or both. Decreased calcium excretion was observed over wide ranges of control calcium excretion, filtered calcium, and sodium excretion. Stop-flow studies show that when parathyroid activity is present, there is a marked fall in urinary calcium concentration at a distal site, whereas there is little or no fall in concentration in its absence. It is concluded that parathyroid extract directly enhances tubular calcium reabsorption, and that this effect is exerted, at least in part, at a distal site.