EFFECTS OF L-CARNITINE ON THE RENAL TUBULAR TRANSPORT OF CEPHALORIDINE

It has been demonstrated recently that cephaloridine (Cld) inhibits th e tubular reabsorption of filtered carnitine (Cam) in the rabbit kidne y. This interaction has suggested that the limited net cell-to-luminal fluid movement of Cld following its secretory transport across the an tiluminal membrane might result from a balance of active Cld reabsorpt ion by a Cam carrier at the brush border approximately equal to its se cretion into the tubular fluid, rather than the previously proposed lu minal membrane block, Studies were done to determine the effects of L- Carn, 750 mg/kg, i.v. on the tubular secretion and cortical concentrat ions of Cld, infused i.v. at a dose of 28 mg/kg (Carn:Cld molar ratio = 70:1). The fractional excretions of Cld during three consecutive per iods of 10 min each, one before and two following the bolus infusion o f Carn, were (means +/- SEM): 1.18 +/- 0.14, 1.20 +/- 0.14, and 1.16 /- 0.11, respectively (N = 6 each; differences NS). Cortex-to-serum co ncentration ratios of Cld in control and Cam-treated rabbits were 10.4 3 +/- 0.32 and 10.16 +/- 0.86, respectively (NS). The data provide evi dence against the reabsorptive transport of Cld by a Cam carrier, and do not support a model of balanced secretion and reabsorption as the c ause of limited clearance despite significant secretory transport of C ld into the tubular cell.