EFFECT OF RADIOCONTRAST AGENTS ON INTRARENAL NITRIC-OXIDE (NO) AND NOSYNTHASE ACTIVITY

Background/Aims: Contrast media (CM) induce a biphasic renal hemodynam ic response, with late prominent cortical vasoconstriction and marked outer medullary vasodilation. The objective of the study was to explor e a possible role for altered nitric oxide (NO) production or bioavail ability in these hemodynamic responses. Methods: We explored the impac t of CM (sodium iothalamate) upon rat renal NO synthase (NOS) activity (citrulline recovery) and NO (using a NO electrode). Results: The cor tical NOS activity following CM was 11.5 +/- 1.0 versus 13.8 +/- 1.1 n mol/gww/min (gww = gram wet weight) in controls (p = 0.16, NS). In rat s pretreated with the nonselective endothelin antagonist bosentan, CM reduced the cortical NOS activity to 8.5 +/- 1.2 nmol/gww/min (p < 0.0 05 vs. controls). Cortial NO readings declined over 30 min following C M by 13 +/- 8% (p < 0.05, Anova), in parallel with the decline in cort ical blood flow. The outer medullary NOS activity was not affected by CM (5.2 +/- 1.5 vs. 5.5 +/- 1.3) nmol/gww/min in controls) or bosentan . Nevertheless, the outer medullary NO reading increased by 36 +/- 23% (p < 0.05), with a concomitant increase in regional blood flow. Concl usion: In the cortex, CM might reduce the NOS activity tan effect blun ted by endothelin release). This may potentiate the effect of endothel in to induce regional vasoconstriction. In the outer medulla, the vaso dilatory response to CM does not seem to be mediated by enhanced NOS a ctivity and might reflect increased local NO bioavailability as the re sult of regional hypoxia.