The thromboxane A2 (TXA2) mimetic U44069 has been demonstrated to reduce the GFR and filtration fraction of the normal isolated perfused rat kidney markedly, suggesting a predominant constriction of preglomerular vessels. To assess this possibility directly, effects of U44069 on the renal microvessels of the isolated perfused hydronephrotic kidney were examined. At 10-6 mol/L, U44069 elicited a 27 ± 2% decrease in afferent arteriolar (AA) diameter (from 18.8 ± 0.3 to 13.7 ± 0.3 μm, P < 0.001). In contrast, efferent arteriolar (EA) diameter decreased by only 9 ± 1% (from 16.4 ± 0.5 to 15.0 ± 0.5 μm, P < 0.001). These effects on both AA and EA were completely reversed by the TXA2 receptor antagonist SQ29548. The calcium antagonist diltiazem reversed U44069-induced AA constriction by 83 ± 5%. The U44069-induced EA constriction was insensitive to the vasodilator action of diltiazem at concentrations from 10-8 to 10-6 mol/L, but at 10-5 mol/L, diltiazem increased the EA diameter significantly, albeit modestly. Nifedipine also reversed the U44069-induced AA constriction (81 ± 7%), but failed to inhibit the EA constriction at concentrations from 10-9 to 10-6 mol/L. These findings constitute the first direct evidence that a TXA2 agonist preferentially constricts the afferent arteriole. Furthermore, the ability of both the calcium antagonist and SQ29548 to reverse the renal microvascular actions of TXA2 agonists suggests a potential utility of these agents in ameliorating TXA2-induced renal hemodynamic abnormalities.
|Number of pages||7|
|Journal||Journal of the American Society of Nephrology|
|Publication status||Published - 1997 Jan 1|
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