Effect of parathyroid hormone activity on gentamicin nephrotoxicity

Dietary calcium (CA++) supplementation attenuates gentamicin nephrotoxicity in rats. It has been proposed that this protective effect results from the ability of Ca++ to interfere with gentamicin binding to renal cell membranes. However, calcium supplementation also suppresses parathyroid hormone (PTH) activity, which may affect gentamicin nephrotoxicity by altering renal brush border phospholipid composition or renal calcium handling. We therefore compared gentamicin nephrotoxicity in PTH-stimulated control rats and parathyroidectomized (PTX) rats. Although their pretreatment serum ionized calcium concentration was significantly higher (1.27 +/- 0.01 vs. 0.88 +/- 0.06 mmol/L; P less than 0.001), PTH-stimulated rats had higher peak renal cortical gentamicin concentrations (543 +/- 20 vs. 395 +/- 49 micrograms/gm; P less than 0.025) and serum creatinine concentrations (3.0 +/- 0.8 vs. 0.9 +/- 0.3 mg/dl; P less than 0.05). Structural injury and depression of renal cortical slice uptake of p-aminohippurate were also less severe in PTX rats. Gentamicin treatment also caused increased urinary Ca++ excretion in control rats (from 2.12 +/- 0.64 mumol/mg creatinine per day [pretreatment] to 16.86 +/- 2.07 mumol/mg creatinine per day; P less than 0.001) but not in PTX rats. Control rats ingesting chow containing a standard Ca++ content (1.2%) resembled PTX rats. These results indicate that PTH stimulation exacerbates gentamicin nephrotoxicity. Increased peak renal cortical gentamicin concentrations in PTH-stimulated rats may be caused by increased gentamicin transport across the brush border as a consequence of PTH-mediated alteration of plasma membrane phospholipid composition, turnover, or both.(ABSTRACT TRUNCATED AT 250 WORDS)