Relationship between Intrarenal Hydrostatic Pressure and Hemodynamically Induced Changes in Sodium Excretion

Abstract

Deep intrarenal venous pressure was used as an index of renal capillary pressure to test the proposal that physically induced changes in sodium reabsorption may be mediated by changes in Starling forces across the capillary. Renal vasodilatation produced natriuresis associated with immediate increases in intrarenal venous pressure. Increased arterial pressure was accompanied by further natriuresis and initially increased intrarenal pressure in vasodilated kidneys. Plasma load was always accompanied by increased intrarenal venous pressure. Saline loading usually increased intrarenal venous pressure, and restoration of plasma protein concentration during saline loading reduced, but did not abolish, natriuresis. This continued natriuresis was associated with reduced renal vascular resistance and increased intrarenal venous pressure, demonstrating that continued natriuresis after restoring plasma oncotic pressure during saline loading could relate to increased capillary hydrostatic pressure. Intrarenal venous pressure did not relate to isolated changes in urine flow, arterial pressure, or renal blood flow. These observations support the hypothesis that changes in peritubular capillary hydrostatic pressure initiate changes in tubular sodium reabsorption as a result of changes in capillary uptake.

Effects of hematocrit on renal hemodynamics and sodium excretion in hydropenic and volume-expanded dogs

“…The observations of de Wardener, Mills, Clapham, and Hayter (16), that natriuresis during saline infusion can be dissociated from the rate of glomerular filtration and mineralocorticoid activity, have led to investigations attempting to define further these additional natriuretic mechanisms. Recent studies have demonstrated the roles of renal perfusion pressure (11,13,14), renal vascular resistance (11,26) plasma protein concentration (11,26), and plasma sodium concentration (27,28) in the natriuretic response to volume expansion. In the present study we examined the effect of increasing the hematocrit to normal values during sustained volume expansion with either saline or plasma.…”

Effects of Dietary Sodium and of Acute Saline Infusion on the Interrelationship between Dopamine Excretion and Adrenergic Activity in Man

“…These changes in renal hemodynamics occur, at least in part, as a result of a direct action of dopamine on the renal vasculature (36), and, as they may be selectively attenuated by haloperidol and chlorpromazine, they are probably mediated by specific dopamine receptors in the kidney (9,10). Whereas changes in renal vasodilatation may be linked to the increase in sodium excretion by virtue of a decrease in colloid oncotic pressure and an increase in hydrostatic pressure in peritubular capillaries such that the tubular reabsorption of sodium is decreased (37)(38)(39), a direct effect of dopamine on tubular transport of sodium may also occur. The observation of a decrease in the tubular reabsorption of sodium which could not be explained in terms of events in the peritubular capillary has led to postulation of the existence of a natriuretic substance or substances (40).…”

Pressure Control of Sodium Reabsorption and Intercellular Backflux across Proximal Kidney Tubule

“…The available data on the effect of peritubular pressure changes in mammalian kidneys do not lend themselves to comparison. Pressure or flux values were estimated only indirectly (10,12,13), and the effects of only small increments of PPT tested.…”