RENAL VASOCONSTRICTION CAUSED BY SHORT-TERM CHOLESTEROL FEEDING IS CORRECTED BY THROMBOXANE ANTAGONIST OR PROBUCOL

Recent studies indicate that short-term cholesterol feeding causes vascular hyperreactivity and/or increased tone in certain vascular beds. The present study in rats examined the effect of 3 wk of cholesterol-supplemented diet (CSD) on renal hemodynamics. We tested the hypothesis that LDL oxidized in vivo is causally related to increased renal vascular tone by adding the antioxidant drug probucol to the CSD (CSD + P). Micropuncture of surface nephrons in the CSD rats demonstrated that single nephron glomeruiar filtration rate (SNGFR) and single nephron afferent plasma flow (QA) were markedly lower than in normal rats, whereas glomerular capillary pressure (PGC), afferent arteriolar resistance (RA), and single nephron filtration fraction (SNFF) were higher. In the CSD + P animals, almost all of these hemodynamic abnormalities were absent. TXB2 and PGE2 were increased in proximal tubule fluid and urine in the CSD rats, but normal in the CSD + P group. Infusion of a TXA2 receptor antagonist into the suprarenal aorta of CSD rats caused a rapid return to normal of RBF (renal blood flow), GFR (glomerular filtration rate), SNGFR, QA, RA, PGC, and Kf (ultrafiltration coefficient). Our observations demonstrate that cholesterol feeding leads to renal vasoconstriction, which appears to be mediated largely by increased TXA2 production. The fact that probucol prevented the hemodynamic abnormalities as well as the increased TX production is consistent with the hypothesis that LDL oxidized in vivo initiates events leading to TX mediated vasoconstriction.