Use of Radiophosphorus in Studies of Glomerular Permeability of Plasma Inorganic Phosphate

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Abstract
When single tracer doses of P32, with or without carrier were intraven. injected into dogs, the specific activity of the urinary inorganic phosphate was found to be as much as 32% above that of the specific activity of the corresponding plasma inorganic phosphate. This difference usually disappeared within 25 min. When the specific activity of the plasma inorganic phosphate was caused to rise, fall or remain constant, the differences in specific activity between urine and plasma inorganic phosphate were markedly altered or entirely abolished. When a small amt. of radioactive plasma from an apparently equilibrated dog was given to a second dog, differences in specific activity of urine and plasma inorganic phosphate were of the same order of magnitude as in animals receiving untreated P32. It is concluded that the greatest part of these differences may be explained on the basis of a lag which exists between the time inorganic phosphate is filtered by the glomerulus and the time at which it reaches the bladder for collection. The evidence suggests that the majority of the inorganic phosphate of plasma exists in a simple, filterable state.