Real-time profiling of kidney tubular fluid nitric oxide concentrations in vivo

Real-time profiling of kidney tubular fluid nitric oxide concentrations in vivo. Am J Physiol Renal Physiol 281: F189-F194, 2001.--To directly determine intratubular nitric oxide concentrations ([NO]) in vivo, we modified amperometric integrated electrodes (WPI P/N ISO-NOP007), which are highly sensitive to NO and not affected by ascorbic acid, nitrite, L-arginine, or dopamine. Although reactive lengths were as short as 5 [micro]m long, the electrode still responded rapidly. With the use of kidney surface fluid as the 'zero point,' the electrode tip was inserted into tubular segments along the track of a perforation made by a beveled glass pipette. The surface fluid zero point was usually stable as distal, late proximal, and early proximal tubule [NO] levels were measured sequentially in the same nephron. In eight normal rats, distal, late proximal, and early proximal [NO] concentrations were each ~110 nM. In contrast, in nine 5/6 nephrectomized rats 2 wk postsurgery, although [NO] also did not differ among distal, late proximal, and early proximal segments, levels were approximately fourfold higher than those in normal rats and were significantly reduced after [N.sup.G]-monomethyl-L-arginine administration. These are the first quantitative in vivo tubular fluid [NO] measurements and show a significant increase in tubular fluid [NO] after renal ablation. kidney tubules; in vivo nitric oxide measurements; remnant kidney