Nitric oxide generation by isolated descending vasa recta

Nitric oxide (NO) generation by the outer medullary descending vasa recta ( OMDVR) was measured with the fluorescent dye 4,5-diaminofluoroscein (DAF-2) during 30-min incubations. Addition of 0.1 or 1.0 mM L-arginine to the inc ubation buffer increased the DAF-2 signal by 8.7 and 13.6% (P = 0.08 and P< 0.05), respectively. Compared with L-arginine alone (0.1 mM), bradykinin ( BK; 1 x 10(-7) M) enhanced the DAF-2 signal by 11.1% (P< 0.05). The NO synt hase inhibitor N-omega-nitro-L-arginine methyl ester (0.1 mM) reversed the BK-stimulated NO generation as measured with either DAF-2 or by the oxidati on of Fe2+ hemoglobin. Using 1 mM 4-hydroxy-2,2,6,6- tetramethylpiperidine- 1-oxyl (tempol), a cell-permeant superoxide dismutase mimetic, we tested wh ether reduction of superoxide anion increases intracellular NO. Tempol incr eased DAF-2 fluorescence by 12 and 23.3%, respectively, over BK-stimulated or control vessels. Tempol also vasodilated ANG II (1 x 10(-8) M)-preconstr icted OMDVR (P, 0.05). We conclude that NO generation by isolated OMDVR can be increased by L-arginine, that the endothelium-dependent vasodilator BK enhances NO production, and that NO consumption by superoxide plays a role in the determination of cellular NO concentrations.