Effect of thoracic cava obstruction on response of proximal tubule sodium reabsorption to saline infusion.

Abstract

We have recently demonstrated that in the normal dog infusion of isotonic or hypertonic saline results in marked depression of sodium reabsorption in the proximal tubule (1). This depression is independent of the effect of saline infusion on filtration rate and is not blocked by reduction of filtration rate. Such depression in proximal tubule reabsorption appears to account for the diuresis known, from the studies of De Wardener, Mills, Clapham, and Hayter (2, 3) and others (4-7), to occur after saline infusion.The present micropuncture study was undertaken to evaluate the possibility that sodium retention in states associated with edema formation might be related to failure of the normal decrease in proximal tubule sodium reabsorption to occur in response to salt loading. Reabsorption in the proximal tubule was evaluated by micropuncture techniques before and after acute partial obstruction of the thoracic, inferior vena cava. Results indicate that the depression of proximal tubule sodium reabsorption that follows saline loading can be prevented and reversed by thoracic cava obstruction. This effect is independent of change in filtration rate or renal venous pressure. MethodsStudies were performed on male and female mongrel dogs weighing 10 to 25 kg. Dogs were rapidly anesthetized by intravenous injection of 25 mg per kg sodium

Increased sodium reabsorption in the proximal and distal tubule of caval dogs

“…Although many factors have been implicated as responsible for sodium retention in the caval dog, it is clear from the experiments of other investigators that the increase in tubular sodium reabsorption cannot be totally explained on the basis of alterations in renal hemodynamics, renal vein pressure, or renal innervation (2,4,11). In the present experiments GFR and ERPF tended to be lower in caval dogs compared with normals during water and hypotonic NaCl diuresis.…”

“…Moreover, it has been demonstrated that either acute or chronic constriction of the thoracic inferior vena cava inhibits or retards the natriuresis usually seen with salt loading (2,3). Micropuncture experiments of Cirksena, Dirks, and Berliner (4) suggest that sodium retention in the caval dog is mediated by an increased fractional sodium reabsorption along the proximal tubule. The possibility that sodium reabsorption is also increased at more distal sites of the nephron has not been explored.…”

Effects of Acute Volume Expansion and Altered Hemodynamics on Renal Tubular Function in Chronic Caval Dogs

“…Dogs with partial, chronic constriction of the thoracic inferior vena cava (chronic caval dog) develop salt and water retention, edema and ascites, and usually respond to acute saline loading with only, at best, a feeble natriuretic response (3,4). It has generally been felt that the minimal sodium excretion observed in chronic caval dogs under conditions of acute saline loading is due to maintenance of sodium reabsorption in the proximal tubule (5).…”

“…The micropuncture experiments which demonstrated that the failure of caval dogs to excrete sodium in response to acute volume expansion was due to maintenance of fractional sodium reabsorption in the proximal tubule were carried out in dogs with acute rather than chronic constriction of the thoracic vena cava (5). Under these conditions, the major changes in systemic hemodynamics, and severe depression of GFR which occurred could easily have explained the observed data.…”

Effect of hypotonic expansion on sodium, water, and urea excretion in late pregnancy: the influence of posture on these results

“…For instance, the natriuresis which follows volume loading of the dog is largely due to a prompt decrease in the tubular reabsorption of sodium which is independent of mineralocorticoid activity (3)(4)(5)(6). In this same species production of experimental salt retention is accompanied by ablation of the tubular natriuretic response (7,8). These tubular natriuretic factors may be operative in normal man and of importance in the sodium homeostasis of patients with chronic renal disease (9, 10).…”