PHOSPHATE EXCRETION AND REABSORPTION IN THE CONSCIOUS DOG

¹ Department of Physiology, University of Leeds, Leeds LS2 9JT
² Department of Chemical Pathology, University of Leeds

When normal conscious dogs were given small doses of (NH₄)₂HPO₄ by stomach tube to increase their plasma PO₄, the rate of excretion of PO₄ increased without change in creatinine clearance. After eating meat, increased PO₄ excretion was accompanied by increase in both creatinine caearance and plasma PO₄. The calculated rate of tubular reabsorption of PO₄ did not change significantly after (NH₄)₂HPO₄ administration, but there was a significant increase in PO₄ reabsorption after meat; in comparison there was no change in SO₄ reabsorption. Similarly, administration of certain amino acids, which caused an increase in creatinine clearance, also caused a significant increase in PO₄ reabsorption. Administration of SO₄ with PO₄ had no significant effect on PO₄ reabsorption. It appears from the results, that PO₄ has an apparent tubular maximum rate of reabsorption (T_m) when plasma PO₄ alone is varied; but this T_m is not a real maximum because PO₄ reabsorption increases above this value after the administration of meat or amino acids, both of which cause an increase in glomerular filtration rate. There is no evidence to suggest that there is any inhibition of PO₄ reabsorption by SO₄ or amino acids.