Sphingosine‐1‐phosphate (S1P) attenuation of acute inflammatory response versus reactive oxygen generation in rat microvessels

Abstract

S1P activates Rac1, stabilizes peripheral actin and modulates permeability responses in intact microvessels. Previous results indicate that S1P (1 μM) inhibits 65% of the peak Lp response to bradykinin (Bk; 10 nM) in rat mesenteric microvessels. In contrast to the protective action of Rac1 above, activated Rac1 also regulates reactive oxygen species (ROS) generation via NADPH oxidase. Further, ROS may mediate Rac1 induced loss of cell‐cell adhesion in endothelium and could increase permeability. Thus we hypothesized that ROS scavenging could enhance S1P dependent permeability inhibition. To test this idea we perfused rat mesenteric microvessels with the ROS scavenger N‐(2‐Mercaptopropionyl)glycine (MPG; 500 μM), and compared the Lp response to Bk (10 nM) in the presence of MPG versus the presence of MPG and S1P (1 μM). The attenuation of the Bk response with S1P in the presence of MPG (to 0.32 ± 0.07, n=8) was not different from the level of attenuation seen in the absence of MPG indicating that ROS generation by S1P does not contribute to vessel Lp increase under these conditions. MPG (w/o S1P) enhanced the Bk response near 2‐fold, suggesting that a low level of ROS present in the tissue decreases the NO‐dependent Bk response via NO destruction. The results are consistent with the hypothesis that S1P acts predominantly though Rac1 activation to strengthen cell‐cell adhesion. Supp NIH HL28607.