INHIBITION OF NITRIC-OXIDE SYNTHESIS INCREASES VENULAR PERMEABILITY AND ALTERS ENDOTHELIAL ACTIN CYTOSKELETON

Inhibition of nitric oxide (NO) synthesis using N-G-nitro-L-arginine m ethyl eater (L-NAME) or N-G-monomethyl-L-arginine (L-NMMA) increases v enular permeability in the rat mesentery (I. Kurose, R. Wolf, M. B. Gr isham, T. Y. Aw, R. D. Specian, and D. N. Granger. Circ. Res. 76. 30-3 9, 1995), but the cellular mechanisms of this response are not known. This study was performed to determine whether such venular leaks are a ssociated with changes in the endothelial actin cytoskeleton. In anest hetized Sprague-Dawley rats, the microvasculature of a mesenteric wind ow was perfused with buffered saline, with or without 10(-5) M L-NAME, L-NMMA, or the inactive enantiomer N-G-nitro-D-arginine methyl ester for 3 or 30 min. FITC-albumin was added to the perfusate for the last 3 min, The vasculature was perfusion fixed, stained for filamentous ac tin and for mast cells, and viewed microscopically. In control prepara tions, venules showed few FITC-albumin leaks and the endothelial actin cytoskeleton consisted of a peripheral rim along the cell-cell juncti ons. Preparations treated with L-NAME or L-NMMA showed significantly m ore leakage, the actin rims in leaky venules were discontinuous, and s hort, randomly oriented fibers appeared within the cells. In nonleaky venules, the peripheral actin rims sometimes contained small, equally spaced discontinuities not seen in control preparations. Although a ma st cell stabilizer was used, 27-70% of the mast cells were degranulate d in the presence of L-NMMA. Thus inhibition of NO synthesis alters th e endothelial cytoskeleton and increases albumin leakage from mesenter ic venules, either directly or indirectly via the involvement of mast cells.