Early enhancement of fluid transport in rabbit proximal straight tubules after loss of contralateral renal excretory function.

Abstract

A B S T R A C T To assess the renal functional adaptation to reduced excretory capacity, we studied whole kidney and single nephron function in anesthetized volume-replete rabbits after unilateral (left kidney) nephrectomy (UNX), ureteral obstruction (UO), or ureteroperitoneostomy (UP). At 24 h, despite the absence of measurable hypertrophy of the contralateral (right) kidney, these procedures significantly increased p-aminohippurate clearance (45-54%) and inulin clearance (CIN) (64-110%) compared with sham-operated control animals. In each group, whole kidney sodium reabsorption increased in proportion to the rise in CINTo determine whether the intrinsic transport capacity of proximal tubule segments is altered by these maneuvers, we measured fluid volume reabsorption rate (Jv) in isolated superficial proximal straight tubule (PST) segments perfused in vitro, comparing each control tubule (obtained by biopsy of the left kidney immediately before an experimental maneuver) with a corresponding tubule segment obtained 24

Glomerular and tubular adaptive responses to acute nephron loss in the rat. Effect of prostaglandin synthesis inhibition.

“…Our reabsorptive data obtained in surface proximal convoluted tubules by in vivo micropuncture techniques in the rat are in agreement with those results recently obtained in isolated, superficial proximal straight tubular segments perfused in vitro 24 h after unilateral nephrectomy in the rabbit (25), in which fluid volume reabsorption rate was demonstrated to be increased and closely related to GFR. However, they are in marked contrast to previous micropuncture studies (28) (13).…”

“…The results from our in vivo micropuncture studies provide evidence that a hyperfunctioning response can be observed in remnant nephrons 24 h after Nx; this response is not dependent on established hypertrophy but depends on enhanced production of vasodilatory prostaglandin. Although there has been controversy as to whether the nephrons ofthe remnant kidney possess the capacity to acutely augment GFR in response to a significant loss of functional renal mass, recent studies in volume replete animals have demonstrated that such kidneys do have a striking capacity to compensate, within 24 h of the loss of renal mass and excretory function, by increasing GFR (25). This increment was ascribed to an increase in RPF (25), a consequence of altered vascular resistances, but resistance changes were not addressed in that study.…”

“…Although there has been controversy as to whether the nephrons ofthe remnant kidney possess the capacity to acutely augment GFR in response to a significant loss of functional renal mass, recent studies in volume replete animals have demonstrated that such kidneys do have a striking capacity to compensate, within 24 h of the loss of renal mass and excretory function, by increasing GFR (25). This increment was ascribed to an increase in RPF (25), a consequence of altered vascular resistances, but resistance changes were not addressed in that study. The present data obtained in free-flow micropuncture studies confirm that acute Nx results in a hyperfiltering state.…”

Load dependence of proximal tubular fluid and bicarbonate reabsorption in the remnant kidney of the Munich-Wistar rat.

“…In most studies, fractional fluid and bicarbonate reabsorption in the proximal tubule have been reduced, as compared to control (3,5,8,9,12 (5,6,8,9). An increase in proximal fluid reabsorption in the isolated perfused nephron of the rabbit remnant kidney has also been observed (13)(14)(15). Because this increase in reabsorption was present even under controlled perfusion rates in the isolated nephron, the results were interpreted to indicate that a memory effect existed and that the intrinsic reabsorptive capacity was augmented (14).…”

“…Fluid reabsorption in the proximal tubule has been measured in the residual nephrons ofthe remnant kidney both under freeflow micropuncture conditions (3,5,6,8,9), and in isolated perfused proximal tubule preparations (13)(14)(15). With two exceptions (3,9), these studies have all demonstrated that the absolute rate of fluid reabsorption in the proximal tubule is increased as compared with control in the remnant kidney.…”