Hypercholesterolemia Aggravates Radiocontrast Nephrotoxicity: Protective Role of L-arginine

It is well known that the radiocontrast-induced ARF depends on risk factors often associated with compromised renal circulation. Since studies have shown that endothelium-dependent vasodilation is impaired in hypercholesterolemia (HC), we studied the effect of radiocontrast (RC) administration (6 ml/kg body wt, via femoral artery) in salt-depleted rats that were kept on a normal cholesterol (NC) or HC diet (4% cholesterol and 1% cholic acid). Inulin clearance (CIn, ml/min/100 g body wt), renal blood flow (RBF; electromagnetic flowmeter, ml/min/100 g body wt), and fractional excretions of sodium, potassium and water (FENa, FEK and FEH2O, respectively), cholesterol (mg/dl), and albumin (g/dl) were measured 24 hours after radiocontrast administration. The administration of RC to HC rats (RCHC) resulted in lower values of CIn compared with NC rats (RCNC) and control rats: 0.36 +/- 0.085 versus 0.76 +/- 0.13 (RCNC; P < 0.01), versus 0.84 +/- 0.03 (control HC; P < 0.01), versus 0.87 +/- 0.06 (control NC; P < 0.01). Hypercholesterolemia per se did not alter renal function, and control HC versus control NC was not significant. Renal blood flow was significantly lower in the RCHC when compared to RCNC (4.3 +/- 0.3 vs. 6.1 +/- 0.3; P < 0.001) and to control animals (control HC 8.2 +/- 0.3; P < 0.001), and control NC 7.5 +/- 0.33 (P < 0.001). To study the role of nitric oxide (NO), HC rats were treated with an infusion of L-arginine or D-arginine (150 mg via femoral artery) in a 50 mg bolus before RC administration and the remaining dose continuously for a period of one hour. The administration of L-arginine to RCHC rats resulted in significantly higher CIn (0.86 +/- 0.1; P < 0.001) when compared to the untreated rats (RCHC). D-arginine did not show a significant difference in CIn (0.49 +/- 0.08). There was a considerable difference between D-arginine RCHC and L-arginine RCHC (P < 0.05). The RBF fall was prevented by L-arginine in RCHC (8.4 +/- 0.23 vs. 4.3 +/- 0.3; P < 0.001), but it was not prevented by D-arginine (5.1 +/- 0.57; P < 0.001). Our data suggest that hypercholesterolemia aggravates nephrotoxicity, which is attenuated by L-arginine but not by D-arginine administration, suggesting that nitric oxide plays a significant role in this model of acute renal failure.