Mechanisms of the defect in glomerular ultrafiltration associated with gentamicin administration
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Abstract:
Micropuncture studies were performed in three groups of Munich-Wistar rats: eight normal hydropenic controls (group I) and two groups (eight rats each) which were treated with gentamicin in doses of either 4 or 40 mg/kg/day for ten days (groups II and III, respectively). Following gentamicin administration, values for single nephron (SN) GFR were reduced markedly, from the control mean of 31 +/- 0.7 (SEM) nl/min to 22.4 +/- 1.5 and 20.5 +/- 0.9 for groups II and III, respectively. Declines in whole kidney GFR paralleled these falls in SNGFR. The primary cause of the reduction in SNGFR was a marked decline in glomerular capillary ultrafiltration coefficient, Kf, in both gentamicin treatment groups. None of the other determinants of glomerular ultrafiltration were significantly affected in the low dose group (group II). In the high dose group (group III), however, mean values for initial glomerular plasma flow rate and mean transglomerular hydraulic pressure difference were significantly lower than in the control group, accounting for the somewhat greater decline in SNGFR observed in group III. Electron microscopic examination of kidney tissue from rats treated with both doses of gentamicin revealed no obvious abnormalities of the glomerular capillary wall, whereas the previously described morphologic aberrations of proximal convoluted tubule cells were readily demonstrable.
Insights
Gentamicin reduces kidney function by decreasing single nephron glomerular filtration rate (SNGFR). This nephrotoxicity is primarily due to a lower ultrafiltration coefficient (Kf), with high doses also affecting plasma flow and pressure.
Area of Science:
- Nephrology
- Pharmacology
- Toxicology
Background:
- Gentamicin is a widely used antibiotic with known nephrotoxic potential.
- Understanding the precise mechanisms of gentamicin-induced kidney damage is crucial for patient safety.
Purpose of the Study:
- To investigate the functional and morphological effects of gentamicin on rat kidneys.
- To determine the primary cause of reduced single nephron glomerular filtration rate (SNGFR) following gentamicin administration.
Main Methods:
- Micropuncture studies were conducted on Munich-Wistar rats divided into control and two gentamicin-treated groups (4 mg/kg/day and 40 mg/kg/day for 10 days).
- Measurements included single nephron glomerular filtration rate (SNGFR), glomerular capillary ultrafiltration coefficient (Kf), glomerular plasma flow rate, and transglomerular hydraulic pressure.
- Kidney tissue was examined using electron microscopy.
Main Results:
- Gentamicin administration significantly reduced SNGFR in both treatment groups.
- The primary cause of SNGFR reduction was a marked decline in the glomerular capillary ultrafiltration coefficient (Kf).
- High-dose gentamicin also decreased glomerular plasma flow rate and transglomerular hydraulic pressure, while electron microscopy showed proximal convoluted tubule cell abnormalities but no glomerular capillary wall changes.
Conclusions:
- Gentamicin induces nephrotoxicity by reducing SNGFR, mainly through decreased Kf.
- High gentamicin doses exacerbate kidney injury by additionally impacting glomerular hemodynamics.
- Morphological damage is evident in proximal tubules, not the glomerular capillary wall.