Autoradiography of tobramycin uptake by the proximal and distal tubules of normal and endotoxin-treated rats

Marois

Kuehn

et al. 1987

Self Cite

Multiple factors may modify the pharmacokinetics of aminoglycosides and affect their nephrotoxic potential. In the present study, the influence of Escherichia coli pyelonephritis on the renal handling of [3H]tobramycin was investigated. The accumulation of [3H]tobramycin in proximal and distal tubules in both normal and infected rats was compared. Following induction of pyelonephritis, disturbed intrarenal localization of the drug was noted. Grain counts were affected in both proximal and distal tubules. Decreased labeling was observed at all time intervals in the proximal tubules. Electron microscopy showed that radioactivity was associated mostly with lysosomes in both normal and infected rats 1 and 24 h following the injection of the drug. We could detect significantly higher amounts of drug in the distal tubules of the pyelonephritic kidney than the normal levels at 10 min and 24 h postinjection. The drug did not seem to be associated with any particular organelle and was evenly distributed within the distal tubular cells. The present study shows that the transport of tobramycin within the infected nephron is disturbed. These data might shed some light on the influence of infection on the intrarenal pharmacology of aminoglycosides.To understand the mechanism of cellular accumulation as well as the cellular transport of aminoglycosides, several investigators have studied the intrarenal disposition of gentamicin by autoradiography (11,18,20). Coupled with electron microscopy, this technique has the unique advantage of allowing recognition of the presence of a labeled compound within tissue and individual cell organelles.The autoradiographic studies that have been done to date agree that the proximal tubule is the primary site of aminoglycoside accumulation. According to the results of these studies, aminoglycosides are generally believed to enter proximal tubule cells by pinocytosis at the luminal cell membrane, with subsequent fusion of endocytotic vacuoles with lysosomes (18,20).No one, however, has yet studied the transport of antibiotics in infected kidneys. On the basis of our previous data, which showed that the intrarenal concentrations of aminoglycosides were disturbed in pyelonephritis (4), we had reason to believe that the distribution of antibiotics, especially aminoglycosides, is disturbed in infected kidneys. tion of the left kidney with 0.1 ml of an inoculum containing 107 to 108 CFU of Escherichia coli Yale. The right kidney was infected by reflux of infected urine into the right ureter, rats being naturally prone to vesico-ureteral reflux. Six uninjected animals served as controls. The animals then had free access to standard rat chow and water. At 4 days after the induction of pyelonephritis, all infected and normal animals were anesthetized with pentobarbital (50 mg/kg of body weight). Polyethylene PE-20 catheters were placed in a jugular vein for intravenous infusions.Each rat was injected intravenously with 50 ,uCi (13 ,ug) of tritiated tobramycin (>2.0 Ci/mmol; 98% pure by thin-layer chrom...

Section: Resultsmentioning

confidence: 99%

Autoradiographic study of tobramycin uptake by proximal and distal tubules of normal and pyelonephritic rats

Marois

Kuehn

et al. 1987

Self Cite

“…In fact, a greater accumulation of drug is observed in the renal cortex and medulla of endotoxin-treated animals than in the kidneys of normal animals (4). How endotoxin interacts with aminoglycosides at the tubular level is unknown, but it increases the uptake of drugs in both the proximal and distal tubules (5). Endotoxin has been shown to disturb the hemodynamic status of the host (14), activate immunological and inflammatory processes (8), induce vasoconstriction (32), and act directly on organelles to induce cell injury (24).…”

mentioning

confidence: 99%

Influence of hydrocortisone succinate on intrarenal accumulation of gentamicin in endotoxemic rats

Beauchamp

1987

Self Cite

Gentamicin is a commonly used antibiotic in the treatment of gram-negative infections including septicemia and pyelonephritis. Bacterial endotoxin is liberated during antibiotic therapy and may lead to endotoxemic shock. Steroids such as hydrocortisone are generally recommended in the treatment of endotoxemic shock. There are very limited data on the influence of endotoxin or corticosteroids on the pharmacology of antibiotics, especially aminoglycosides, which are nephrotoxic. We studied the influence of both Escherichia coli endotoxin and hydrocortisone succinate on the renal uptake of gentamicin in rats. Animals were injected intravenously with endotoxin (0.25 mg/kg) and/or hydrocortisone (25 mg/kg) plus gentamicin (10 mg/kg). Gentamicin levels in the serum and renal parenchyma as well as renal function and histology were evaluated. Both endotoxin and hydrocortisone given alone increased the concentration of gentamicin in the renal cortex (P < 0.05). Normal values in serum were observed in all groups at most time intervals. When administered together, endotoxin and hydrocortisone did not potentiate each other. The combination of endotoxin and hydrocortisone gave significantly higher levels of gentamicin than endotoxin or hydrocortisone alone when endotoxin was injected 3 h before hydrocortisone (P < 0.05). Blood pressure and cardiac frequency were normal when gentamicin was given. Endotoxin alone slightly decreased the glomerular filtration rate, and hydrocortisone alone slightly modified renal plasma flow. The combination of both drugs did not significantly affect renal function. No histological lesion was noted on light microscopy in animals receiving endotoxin. Competitive or synergistic activity of endotoxin, gentamicin, and hydrocortisone at the cellular level, especially on membranes or lysosomes, might explain in part our observation on the renal uptake of gentamicin. By increasing the total amount of drug within the kidney, endotoxin and hydrocortisone might increase the risk of nephrotoxicity associated with aminoglycosides.Previous studies done in our laboratory revealed that the intrarenal distribution of gentamicin is disturbed in experimental pyelonephritis owing to Escherichia coli (7). Pyelonephritic kidneys were also shown to be more susceptible to the nephrotoxic potential of gentamicin than normal kidneys (3). The mechanism by which infection of the kidney influences the intrarenal pharmacology and the nephrotoxic potential of gentamicin is not known. Endotoxin is liberated during antibiotic therapy (29), and it may disturb the intrarenal pharmacokinetics of gentamicin (4). In fact, a greater accumulation of drug is observed in the renal cortex and medulla of endotoxin-treated animals than in the kidneys of normal animals (4). How endotoxin interacts with aminoglycosides at the tubular level is unknown, but it increases the uptake of drugs in both the proximal and distal tubules (5). Endotoxin has been shown to disturb the hemodynamic status of the host (14)

“…Studies from our laboratory revealed increased uptake of aminoglycosides in kidneys of animals suffering from pyelonephritis or receiving endotoxin (1)(2)(3). Synergistic toxicity of endotoxin and tobramycin was also seen in rabbit proximal tubular cells grown in primary cultures (V. Joly, M. G. Bergeron, G. Friedlander, Y. Bergeron, C. Amiel, and C. Carbon, Program Abstr.…”

mentioning

confidence: 99%

Influence of indomethacin on the intrarenal uptake of gentamicin in endotoxemic rats

Tardif

et al. 1989

Self Cite

Gentamicin is a commonly used antibiotic for the treatment of gram-negative-bacterial infections. Bacterial endotoxin is liberated during antibiotic therapy, and we have shown that endotoxemic animals accumulate more aminoglycosides in their renal parenchyma than normal animals. Vasoactive mediators, such as prostaglandins and thromboxanes, are released after endotoxin and are involved in inflammation. Indomethacin, a nonsteroidal anti-inflammatory drug known to inhibit the synthesis of these hormones, was infused intravenously as a bolus (3.0 mg/kg) or as a bolus followed by a continuous infusion (0.75 mg/kg per h) to rats given gentamicin. Levels of gentamicin in serum and kidney were increased 2 h post-antibiotic treatment in the endotoxemic animals. Renal function was not significantly disturbed. Indomethacin given as a bolus failed to correct the disturbed intrarenal pharmacokinetics of gentamicin induced by endotoxin. However, a bolus followed by continuous infusion of indomethacin resulted in low cortical and high papillary levels of antibiotic. These changes were correlated with the inhibition of prostaglandin synthesis from the kidney. These observations suggest an important role for prostaglandins in the interaction among endotoxin, aminoglycosides, and the kidney. Specific inhibitors of arachidonic acid metabolites should be investigated to further understand the mechanisms of this interaction.Several observations indicate a relationship between endotoxemia and impairment of renal function (5, 9). Studies from our laboratory revealed increased uptake of aminoglycosides in kidneys of animals suffering from pyelonephritis or receiving endotoxin (1-3). Synergistic toxicity of endotoxin and tobramycin was also seen in rabbit proximal tubular cells grown in primary cultures (V. Joly, M. G. Bergeron, G. Friedlander, Y. Bergeron, C. Amiel, and C. Carbon, Program Abstr. 28th Intersci. Conf. Antimicrob. Agents Chemother., abstr. no. 291, 1988). Endotoxin is known to disturb the hemodynamic status of the host, activate immunological and inflammatory processes, and act directly on organelles to induce cell injury. In response to endotoxin, vasoactive mediators such as prostaglandins and thromboxanes are released from blood cells and tissues and are responsible for inflammation and vasoconstriction-vasodilation cycles with subsequent lung, heart, and kidney injury (7).The aim of the present study was to evaluate a possible indirect influence of endotoxin upon the intrarenal uptake of gentamicin by blocking the liberation of prostaglandins with the use of indomethacin. Indomethacin is a nonsteroidal anti-inflammatory drug which is known to neutralize the enzyme cyclooxygenase, which catalyzes the catabolism of arachidonic acid into prostaglandins, thromboxanes, and prostacyclins. Indomethacin has also been shown in some experimental studies to improve circulatory status and survival (6).(These data were presented in part at the 26th Interscience Conference on Antimicrobial Agents and Chemotherapy, New Orleans, La....