The nitric oxide pathway is amplified in venular vs arteriolar cultured rat mesenteric endothelial cells

To determine if there are differences in nitric oxide activity between pre- and postcapillary microvessels, we studied cultured rat mesenteric arterio lar and venular endothelial cells (RMAEC, RMVEC). We measured expression of endothelial nitric oxide synthase (eNOS), the activity of eNOS, and L-argi nine transport in live RMAEC and RMVEC and the L-arginine content of RMAEC and RMVEC lysates. The abundance of eNOS was significantly greater in RMVEC vs RMAEC; this was also true for freshly harvested, pooled microvessels. B aseline NOS activity was higher in RMVEC than in RMAEC. N-G-Monomethyl-L-ar ginine (L-NMA; 5 mM) inhibited NOS activity by similar to 70-80% in both RM AEC and RMVEC, indicating that metabolism of L-arginine is largely via NOS. Intracellular L-arginine levels were higher in RMVEC vs RMAEC and well abo ve the eNOS K-m in both cell types. L-Arginine levels increased with L-NMA in both RMAEC and RMVEC, presumably due to reduced substrate utilization. S ince L-arginine transport was not higher in RMVEC vs RMAEC, this may reflec t higher intracellular arginine synthesis. A higher intrinsic level of base line NO production in the postcapillary microvascular endothelium may refle ct both the contribution of venular derived NO to control of arteriolar ton e and a key role of venular-derived NO in local thrombosis Control. (C) 200 1 Academic Press.