Capillary hydraulic conductivity is decreased by nitric oxide synthase inhibition

Nitric oxide (NO) has been reported to modulate microvascular permeability to solutes in whole organs, venules, and cultured endothelial cell monolayers. NO derived from L-arginine via NO synthase activates soluble guanylate cyclase in vascular smooth muscle and endothelial cells. While the effects of NO on capillary water permeability have not been characterized, other activators of guanylate cyclase, such as sodium nitroprusside and atrial natriuretic peptide, increase capillary hydraulic conductivity (Lp). We hypothesized that inhibition of NO synthase with the arginine analogue, NG-monomethyl-L-arginine (L-NMMA), would decrease Lp from control levels. Lp was assessed in situ in single perfused frog mesenteric capillaries, first during control conditions (Lcontrolp) and then during superfusion (Ltestp) with either L-NMMA, NG-monomethyl-D-arginine (D-NMMA), a biologically inert enantiomer, or L-NMMA and L-arginine. Superfusion with 1 microM L-NMMA caused a decrease in Lp (Ltestp/Lcontrolp = 0.6 +/- 0.1, P < 0.001), whereas 1 microM D-NMMA was without effect on Lp (Ltestp/Lcontrolp = 1.0 +/- 0.2). The decrease in Lp by 1 microM L-NMMA was not only prevented by the presence of excess L-arginine (100 microM), but Lp increased from control (Ltestp/Lcontrolp = 1.4 +/- 0.2, P < 0.05). Furthermore, superfusion of L-arginine (100 microM) caused an increase in capillary Lp (Ltestp/Lcontrolp = 2.4 +/- 0.9, P < 0.05), whereas D-arginine had no effect on Lp (Ltestp/Lcontrolp = 1.2 +/- 0.3). The results of this study support our hypothesis that inhibition of NO synthase decreases capillary Lp in the intact circulation. In addition, L-arginine increases capillary Lp in our model.(ABSTRACT TRUNCATED AT 250 WORDS)