Renal regulation of phosphate excretion in the pig

Young pigs of about 25 kg in weight were given supplements of Na2HPO4 either in their food or by intravenous infusion and the effects on urinary phosphate excretion were studied. The results obtained showed that the amount of inorganic phosphate excreted in the urine increased with increase in the amount of phosphate filtered at the glomerulus. A threshold value for phosphate excretion in these pigs occurred at a plasma concentration of 2-03 mmol/l. while over a wide range of filtered phosphate load (0-21-1-14 mmol/min) phosphate was reabsorbed at a mean maximum rate of 0-19 mmol/min. Parathyroidectomy did not alter the relationship between phosphate excretion and filtered phosphate load which suggests that in the pig adjustment of renal phosphate excretion in relation to filtered load is not dependent upon parathormone.