Changes in Renal Blood Flow and Possibly the Intrarenal Distribution of Blood during the Natriuresis Accompanying Saline Loading in the Dog*

The effects of combined renal vasodilatation and pressor agents on renal hemodynamics and the tubular reabsorption of sodium.

“…These observations strengthen the concept that it is the vasodilatation which results in diminished reabsorption of sodium and not some more direct effect of the infused agent on tubular transport (14). We have suggested previously that increased renal medullary blood flow may diminish the absolute reabsorption of sodium by the ascending limb of Henle's loop (4,5), and Leyssac has suggested that angiotensin may diminish proximal tubular reabsorption of sodium (15). Although the effects have not been entirely predictable, angiotensin does produce natriuresis under some conditions (16)(17)(18)(19).…”

“…To a large extent the present results are consistent with this view. In the presence of renal vasodilatation the infusion of angiotensin invariably was associated with natriuresis that in some cases was comparable to that associated with saline loading (2,5).…”

“…Since the report by De Wardener, Mills, Clapham, and Hayter (1), several other studies employing clearance techniques have demonstrated diminished net tubular reabsorption of sodium during saline loading in the dog (2)(3)(4)(5). In addition, Dirks, Cirksena, and Berliner have reported recently that fractional reabsorption in the proximal nephron of the dog may be diminished strikingly during saline loading (6).…”

“…However, such studies have not revealed mechanisms and pathways whereby expansion of the extracellular volume leads to diminished reabsorption of sodium. We recently suggested that increased renal blood flow, and perhaps increased medullary blood flow specifically, may be one factor that by way of intrarenal mechanisms contributes to diminished reabsorption of sodium during saline loading (5). Furthermore, natriuresis in the absence of salt loading accompanies increased renal blood flow when local vasodilatation is produced by a variety of agents (7)(8)(9)(10)(11)(12)(13), and we have observed that the unilateral natriuresis accompanying increased renal blood flow during the renal arterial infusion of acetylcholine is due in part to diminished net tubular reab-sorption of sodium (14).…”

Studies on the Mechanism of Sodium Excretion during Drug-induced Vasodilatation in the Dog

“…Direct micropuncture studies have shown that neither bradykinin nor prostaglandin E2 alters proximal tubular sodium reabsorption (2). Earley and Friedler (3) suggested that renal vasodilatation may cause a natriuresis as a consequence of the washout of the hypertonic medullary interstitium occurring in this setting. Furthermore, recent studies from this laboratory have suggested that medullary washout may preferentially depress sodium reabsorption in the more inner cortical nephrons (4).…”