Leakage responses to l-NAME differ with the fluorescent dye used to label albumin

Nitric oxide synthase (NOS) inhibitors have been reported to increase as well as to decrease microvascular transport of macromolecules in a variety of models. This study was performed to determine whether the influence of NOS inhibition on albumin leakage was dependent on the fluorescent dyes used to label albumin. Albumin leakage was assessed in rat mesenteric venules during control conditions and after exposure to the NOS inhibitor N G-nitro-l-arginine methyl ester (l-NAME). Albumin was labeled with any one of four dyes: FITC, sulforhodamine 101 [Texas Red (TR)], dichlorotriazinyl aminofluorescein (DTAF), or Oregon Green 514 (OG). Superfusion withl-NAME (10−4 M) was accompanied by an increase in leakage of FITC-labeled albumin ( n = 12) but not of albumin labeled with DTAF ( n = 10), TR ( n = 10), or OG ( n = 4). In vessels perfused with both FITC- and TR-labeled albumin ( n = 12), superfusion with l-NAME increased leakage of FITC- but not TR-labeled albumin. In conclusion, albumin leakage responses tol-NAME differ among various fluorescent dyes. Therefore, caution is advised in comparison of albumin leakage results that utilize different fluorescent dyes.

Microvascular transport is associated with TNF plasma levels and protein synthesis in postischemic muscle

To better understand the mechanisms of ischemia-reperfusion (I/R) injury, we tested the hypothesis that protein synthesis is involved in the production of tumor necrosis factor (TNF) and in the microvascular transport changes in I/R. To evaluate the hypothesis, we inhibited protein synthesis with topically applied actinomycin D (AMD), measured I/R-induced changes in microvascular transport, and bioassayed the venous plasma levels of TNF. The rat cremaster muscle I/R model consisted of 4 h of ischemia followed by 2 h of reperfusion. Changes in transport were determined by integrated optical intensity (IOI) using FITC-Dextran 150 as tracer. Animals were separated into four groups: 1) control (C), 2) control treated with AMD (C + AMD), 3) I/R, and 4) I/R treated with AMD (I/R + AMD). The mean (±SE) maximal IOI in C and C + AMD were 3.0 ± 1.0 and 3.7 ± 0.7 units, respectively. I/R elevated mean maximal IOI to 21.8 ± 1.9 units ( P < 0.05 vs. C, C + AMD, I/R + AMD). Treatment with AMD reduced the I/R-induced mean maximal IOI to 9.7 ± 2.0 units ( P< 0.05 vs. I/R). In I/R group, plasma TNF levels increased (relative to preischemia baseline) immediately after the release of the vascular occlusion to 250 pg/ml and reached a peak value of 342 pg/ml at 60 min of reperfusion. In the I/R + AMD group, AMD reduced TNF increase to 44 pg/ml. The C and C + AMD groups showed no differences in TNF values during the 6 h of observation. We conclude that protein synthesis and TNF generation are at least partially involved in I/R-induced changes in microvascular transport.