Localization and characterization of sodium transport along the renal tubule

A Long Affair with Renal Tubules

This essay provides a summary of my professional activities. My interest in renal physiology started as a medical student in Vienna, when I became acquainted with Homer Smith's essays on kidney function. After moving to the United States in 1951, I was fortunate to be mentored by Robert Pitts, in whose Department of Physiology at Cornell Medical College in New York I was given early independence, intellectual stimulation, and the opportunity to pursue experiments on single renal tubules. The problem of how the nephron manages its myriad of transport functions has never lost its fascination for me, and I am profoundly grateful to the many colleagues at Cornell Medical College and at Yale University School of Medicine who shared my passion for the kidney.

Effects of torasemide on renal haemodynamics and function in anaesthetized dogs

1. We examined the effects of torasemide (0.3 and 1 mg/kg i.v.) on renal haemodynamics and function employing renal clearance and stop-flow techniques in anaesthetized dogs and compared these with furosemide (1 and 3 mg/kg i.v.). 2. Torasemide and furosemide did not influence renal haemodynamics, in the renal clearance study, but caused a dose-related and significant increase in urine flow and urinary excretion of sodium and potassium. Torasemide and furosemide increased fractional excretion of sodium in the distal tubules with a relatively small increase in the fractional excretion of lithium (index of sodium excretion at the proximal tubules, FELi). The diuretic profile of torasemide was of long duration, compared with that of furosemide. 3. Torasemide and furosemide inhibited sodium reabsorption at the distal portion of the tubules in the stop-flow study. 4. It is suggested from these results, that the main diuretic site of action of torasemide is the ascending limb of the loop of Henlé.

Renal physiology of the pig: application of stop-flow

1. The stop-flow method in the pig, with modified kidneys, produced patterns for sodium, chloride, glucose and PAH that were similar to those obtained previously in other animals with simple kidneys. 2. Ethacrynic acid, under the conditions of the experiment, abolished distal sodium and chloride reabsorption in the pig. 3. We conclude that this method, viewed in perspective, could provide useful in situ information about the physiology of modified kidneys where the more difficult micropuncture and in vitro perfusion techniques are impractical.

Effect of atrial peptide on collecting duct function

1. The effects of synthetic rat atrial natriuretic peptides (ANP) on diffusional 22Na+, 36Cl- and tritiated water (THO) permeability of in vitro microperfused rat papillary collecting ducts and the effect in vivo of ANP on stop-flow sodium concentrations in the terminal segment of rabbit nephrons were studied. 2. The addition of 4 x 10(-8) or 4 x 10(-7) mol/l ANP to the medium or perfusion solution did not alter diffusional 22Na+ or 36Cl- permeability of microperfused rat papillary collecting ducts. 3. The basal diffusional THO permeability of papillary collecting ducts was not altered when 4 x 10(-7) mol/l ANP was present in the medium and did not inhibit the increment in diffusional THO permeability induced by vasopressin or reduce the permeability to water in a duct previously stimulated by vasopressin. 4. The administration of ANP (2 micrograms/kg bodyweight) to rabbits in water diuresis did not alter systemic blood pressure but induced a marked natriuresis and increases in urine flow and potassium excretion. This natriuresis was not associated with alterations in stop-flow sodium reabsorptive capacity or sodium permeability of the collecting tubules and ducts. 5. Previously reported in vivo clearance data suggest that ANP causes, at least in part, a natriuresis by altering sodium transport in the medullary collecting ducts. In this study, however, a direct effect could not be demonstrated and it is possible that the medulla needs to be functioning in its normal environment for such effects to be demonstrated.

Effect of atrial natriuretic peptide on collecting duct function evaluated by stop-flow in rabbits

1. The effect of a low dose of a synthetic atrial natriuretic peptide (ANP), rat atriopeptin II (23 amino acids), on stop-flow sodium concentrations was examined in rabbits in water diuresis. 2. Atrial natriuretic peptide (2 micrograms/kg body weight) was injected intravenously as a bolus either before or after the commencement of stop-flow. 3. Atrial natriuretic peptide induced a significant natriuresis within 2 min of injection. This natriuresis was associated with smaller increases in urine volume and potassium excretion. Atrial natriuretic peptide did not alter blood pressure. 4. Atrial natriuretic peptide did not significantly alter stop-flow sodium concentrations. 5. These findings indicate that ANP does not directly alter sodium transport across medullary collecting ducts. 6. It is proposed that ANP acts via a mediator to alter sodium movement across terminal segments of the nephron.

Excretion of sodium and methylglucamine diatrizoate after longtime unilateral ureteric stasis in the rabbit

The excretion of sodium and meglumine diatrizoate was examined following one or two weeks of unilateral ureteric occlusion. No difference between the two diatrizoate salts was found. A slow compensatory increase of the function of the intact kidney occurred, but after two weeks it was still insufficient at high blood concentration levels.

Effect of ouabain on renin secretion in anaesthetized dogs

1. Pentobarbitone anaesthetized dogs were used to study the effects on renin secretion of ureteral occlusion and partial aortic clamping before and after intrarenal arterial administration of ouabain.2. Arterial plasma renin activity (A renin) and renal venous minus arterial plasma renin activity (RV-A renin) were both increased by either ureteral occlusion during mannitol diuresis or partial aortic clamping to reduce renal perfusion pressure. Intrarenal arterial ouabain administration blunted or abolished the effects of these manoeuvres on A and RV-A renins.3. The observations are not consistent with the hypothesis that renin secretion is uniquely controlled by afferent arteriolar transmural pressure. Both ureteral occlusion and aortic clamping reduce this pressure and increase renin secretion, yet evidence presented herein suggests that ouabain, which also decreases this pressure, decreases renin secretion.4. The observations are consistent with the hypothesis that renin secretion is controlled by tubular fluid flow and/or composition in the region of macula densa cells. Possibly changes in flow and/or composition are detected as changes in macula densa intracellular sodium concentration.