The Relation between the Urinary Excretion of Inorganic Phosphate and Sodium

Abstract

1. The relation between the urinary excretion of inorganic phosphate and sodium was studied in anaesthetized dogs subjected to acute unilateral increases of ureteral back-pressure while receiving infusions of iso-osmotic sodium chloride. Under these circumstances modest increases of ureteral back-pressure, + 14 to +23 cmH 20, were associated with relatively small changes ofglomerular filtration rate from control values ( -12,7 to +8·2%).2. Increased ureteral back-pressure caused closely proportionate decreases of urinary phosphate and sodium excretion regardless of whether glomerular filtration rate increased, decreased or remained unchanged. When glomerular filtration rate increased or remained stable, the decreases of phosphate and sodium excretion were attributable to closely proportionate increases of tubular reabsorption of sodium and of phosphate. The increased tubular reabsorption of phosphate may be causally related to the increased tubular reabsorption of sodium.The urinary excretion of inorganic phosphate (UpV) increases when the excretion of sodium is increased by the i.v, administration of iso-osmolal NaCI ('saline') in amounts that cause expansion of extracellular fluid volume (ECFV) (Frick, 1968;Massry, Coburn & Kleeman, 1969;Suki, Martinez-Maldonado, Rouse & Terry, 1969). The phosphaturia has been attributed mainly to decreased tubular reabsorption of P (Frick, 1968;Massry et al., 1969;Suki et al., 1969) which parallels the decreased tubular reabsorption of Na (Massry et al., 1969). It is uncertain whether the decreased tubular reabsorption of phosphate (Tp) is secondary to the decreased reabsorption of sodium (TNJ, or whether both events are coincidental but independent effects of ECFV expansion. The present study set out to consider whether Tp and TNa might also exhibit parallel behaviour in the opposite direction, that is, whether increases of TNa might be accompanied by increases of Tp.Moderate increases of ureteral back-pressure (approx. 2~cmH 20) usually cause decreases

Effects of Ethacrynic Acid and Frusemide on Urinary Phosphate in the Dog

“…Data from the literature suggest that there is a correlation in the renal handling of sodium and phosphate in the proximal tubule during different experimental conditions (Massry, Coburn & Kleeman, 1969;Suki, Martinez-Maldonado, Rouse & Terry, 1969;Agus, Puschett, Senesky & Goldberg, 1971 ;Fulop & Brazeau, 1971 ;Puschett, Agus, Senesky & Goldberg, 1972). However, the final changes in the urine indicate a dissociation in the distal tubule (Agus et al, 1971 ;Maesaka et al, 1973).…”