Experimental gentamicin nephrotoxicity: effect of streptozotocin-induced diabetes.

To determine the effect of diabetes mellitus on gentamicin nephrotoxicity we treated male F344 rats with streptozotocin 22 mg/kg (DM rats). DM rats were compared to controls (C) and nondiabetic rats ingesting the osmotic diuretic isosorbide administered to simulate glycosuric diuresis (C/I). Base-line C/I renal function and histology did not differ from C. However, in DM rats base-line inulin clearance (CIN) was 20% lower, and renal cortical slice uptake of p-aminohippurate was reduced compared to C and C/I. DM rats also had foci of renal tubular epithelial dysplasia not seen in C or C/I. Gentamicin was administered at 40 mg/kg-day to C and C/I and 32 mg/kg-day to DM rats to adjust for base-line CIN. Acute tubular necrosis, associated with depression of CIN and renal cortical p-aminohippurate and N-methylnicotinamide uptake, developed in all three groups. There were no differences between C and C/I. However, the degree of acute tubular necrosis and dysfunction was less in DM rats than C and C/I. Renal cortical gentamicin accumulation was also slower in DM than either C or C/I, and changes in renal cortical gentamicin over time followed a different pattern in DM rats. These results indicate that 1) attenuation of gentamicin injury in DM rats may be related to reduced accumulation of gentamicin by the renal cortex, 2) this reduced accumulation may be due to subtle baseline tubular injury mediated by streptozotocin or the diabetic state, and 3) osmotic diuresis does not account for attenuation of renal injury in DM.

cis-diamminedichloroplatinum(II) nephrotoxicity: tubular function after rescue with sodium diethyldithiocarbamate in rats.

Sodium diethyldithiocarbamate (DDTC) administered following cis-diamminedichloroplatinum(II) (DDP) has been reported to attenuate structural renal damage and elevation of blood urea nitrogen in rats. Since DDP damages primarily proximal tubular epithelium in this species, we compared proximal tubular function, glomerular function, and histology in male Sprague-Dawley rats treated with DDP followed by either DDTC or 0.9% NaCl solution (NS) rescue. Male Sprague-Dawley rats received a single i.p. injection of DDP (7.5 mg/kg)-mannitol (75 mg/kg)-NaCl (67.5 mg/kg). Forty-five min later, rats were given i.p. injections of either DDTC (750 mg/kg) dissolved in 0.5 ml of NS (DDP + DDTC group; ten rats) or 0.5 ml NS (DDP + NS group; nine rats); additional rats received either DDTC only (DDTC group; six rats) or no treatment (untreated control group; six rats). All groups were sacrificed 5 days later by ether anesthesia and exsanguination. Compared to the untreated control group, the DDTC group had slightly lower mean blood urea nitrogen at sacrifice [12.5 +/- 0.5 (S.E.) versus 15.4 +/- 0.8 mg/dl; p less than 0.025 by unpaired Student's t test]; there was no difference in serum creatinine. The DDP + DDTC group had no diarrhea and no presacrifice deaths in contrast to diarrhea and three presacrifice deaths in the DDP + NS group. Blood urea nitrogen was also lower in the DDP + DDTC group at sacrifice (187 +/- 30 versus 383 +/- 39 mg/dl; p less than 0.005). However, weight loss and serum creatinine were not different. Structural acute tubular necrosis was marked in both DDP groups but was less severe in the DDP + DDTC group than in the DDP + NS group. Proximal tubular function was indexed by the uptake of the organic base N-[14C]methyl nicotinamide (NMN) and the organic acid p-aminohippurate in renal cortical slices incubated 90 min in Cross and Taggart medium. NMN uptake (expressed as slice to medium ratio) was slightly lower in the DDTC group than in untreated controls (4.1 +/- 0.2 versus 5.0 +/- 0.2; p less than 0.025). Marked depression of p-aminohippurate and NMN uptake occurred in both DDP + DDTC and DDP + NS groups. There was no difference in NMN uptake, but depression of p-aminohippurate uptake was slightly less severe in the DDP + DDTC group (5.3 +/- 0.7 versus 3.1 +/- 0.3; p less than 0.005). We conclude that DDTC rescue attenuates structural DDP injury in this animal model. DDP-mediated proximal tubular dysfunction was only marginally attenuated by DDTC; glomerular filtration rate, as indexed by serum creatinine, was not protected. DDTC attenuation of DDP toxicity may be mediated in part via reducing volume depletion due to DDP-associated diarrhea.

Gentamicin nephrotoxicity. II. Definition of conditions necessary to induce acquired insensitivity.

Acquired insensitivity to the nephrotoxic effects of gentamicin develops in Fischer 344 rats after 10 to 14 days' treatment after development of histologic acute tubular necrosis in a setting of extensive histologic regeneration. To determine the relative importance of aminoglycoside exposure, necrosis, and regeneration in the induction of insensitivity, we examined the effect on gentamicin toxicity of prior non-aminoglycoside-mediated tubular necrosis, antecedent nonnecrotizing aminoglycoside exposure, and unilateral Nx-induced renal tubular hyperplasia. Pretreatment with potassium dichromate, which causes tubular necrosis in the same part of the renal cortex as gentamicin, reduced gentamicin-mediated elevation of Scr but had little effect on gentamicin-related tubular dysfunction or structural damage. Pretreatment with netilmicin, which does not cause tubular necrosis, increased the sensitivity of the kidney to gentamicin; toxicity occurred earlier and was more severe. Antecedent unilateral Nx had no demonstrable effect on susceptibility to gentamicin-associated dysfunction, but histologic renal tubular epithelial regeneration and recovery from dysfunction occurred earlier, These results suggest that necrosis and/or regeneration is the major prerequisite for development of gentamicin insensitivity and that the onset of insensitivity is temporally related to the appearance of necrosis and regeneration. However, non-aminoglycoside-mediated necrosis and regeneration fail to fully-re-create insensitivity, suggesting that exposure to gentamicin is also necessary.

Gentamicin nephrotoxicity. I. Degree and permanence of acquired insensitivity.

Insensitivity to the nephrotoxic effects of gentamicin develops in F344 rats during the course of gentamicin-mediated acute renal failure. Functional and structural recovery occur thereafter in spite of continued gentamicin administration. To determine the degree of insensitivity, we compared structural and functional recovery of rats treated continuously with gentamicin to rats in which gentamicin was stopped after 14 days, at the height of dysfunction. Continued treatment did not reduce the rate or ultimate degree of recovery of structure, CIn, or in vitro renal cortical PAH uptake; however, both the rate and degree of recovery of NMN uptake were reduced in continuously treated animals. Furthermore, doubling the dose of gentamicin during the recovery period overcame insensitivity, causing a second episode of acute renal failure. The permanence of insensitivity was examined by re-treating rats 6 months after recovery from gentamicin-mediated acute renal failure. There was no evidence of residual resistance to gentamicin nephrotoxicity in these animals. These results indicate that although gentamicin insensitivity is substantial, it is not complete, as indicated by low-grade, ongoing tubular toxicity to the organic base transport system and sensitivity to higher doses of gentamicin. Furthermore, insensitivity is a transient phenomenon.