NG-monomethyl L-arginine inhibits endothelium-derived relaxing factor-stimulated cyclic GMP accumulation in cocultures of endothelial and vascular smooth muscle cells by an action specific to the endothelial cell.
The effect of NG-monomethyl L-arginine (LNMMA), an analogue of L-arginine (a proposed precursor of endothelium-derived relaxing factor [EDRF]), on EDRF release from bovine pulmonary artery endothelial cells was investigated using endothelial cell-vascular smooth muscle cocultures and a superfused column containing endothelial cells grown on microcarrier beads. Cocultures were stimulated with control buffer, ATP, bradykinin, melittin, A23187, or nitroprusside in the presence and absence of varying concentrations of LNMMA (30-300 microM). LNMMA caused significant, concentration-dependent decreases in cyclic GMP accumulation in response to the endothelium-dependent dilators bradykinin, ATP, melittin, and A23187 but had no effect on control or nitroprusside-stimulated cocultures. The inhibitory effect of LNMMA on cyclic GMP accumulation was partially reversed by treatment with L-arginine, but was unaffected by D-arginine. To determine the specific site of action of LNMMA, endothelial cells on microcarrier beads were placed in a column and superfused with buffer. The effluent from the column was collected in 30-second (1.5-ml) fractions into 2-cm2 monolayer wells of vascular smooth muscle cells before and after addition of agonists (bradykinin, A23187) to the column inflow. The cyclic GMP content of each well of smooth muscle cells was determined as an index of EDRF activity. LNMMA superfused through the endothelial cell column inhibited cyclic GMP accumulation in vascular smooth muscle cells induced by bradykinin and A23187. LNMMA introduced into the effluent from the endothelial cell column had no effect on smooth muscle cyclic GMP levels. We conclude that LNMMA is an effective, specific inhibitor of EDRF production or release, and its action is specific to the endothelial cell.