MACROPHAGE-INDUCED NITRIC-OXIDE AND PROSTANOID DEPENDENT RELAXATION OF ARTERIAL SMOOTH MUSCLES

We have studied mechanisms of vasodilation induced by supernatant flui d of rat macrophages (Mo), using an arterial bioassay preparation. The cells emigrated by an intraperitoneal injection of thioglycollate wer e isolated and cultured for 12 h in RPMI 1640 medium with and without 2.0 mM L-arginine. More than 98% of the isolated cells clearly demonst rated Wright's esterase staining and phagocytosis of acetylated low-de nsity lipoprotein. The bioassay preparation was made of dog isolated f emoral arteries with and without the endothelium. The supernatant of m acrophages cultured in the L-arginine-free RPMI 1640 caused a signific ant reduction of the precontraction in the bioassay rings, being appro ximately 51.6-66.7% of sodium nitroprusside (SNP) induced maximum vaso dilation in each ring. The supernatant of macrophages cultured in the RPMI 1640 containing 2.0 mM L-arginine produced a significantly smalle r relaxation (similar to 32.3-33.3%). The Mo-induced vasodilation was significantly inhibited by the coculture of the macrophages with 1 mu M dexamethasone, 10 mu M cycloheximide, 50 mu M N-omega-nitro-L-argini ne methyl ester (L-NAME), 10 mu M indomethacin, or 10 mu M aspirin. Th e L-NAME-induced inhibition was significantly reversed by an additiona l treatment with 100 mu M L-arginine. The coculture with both L-NAME a nd indomethacin caused a reduction of the Mo-induced vasodilation (sim ilar to 12.5-13.4%) similar to reductions produced by dexamethasone (s imilar to 10.8-12.1%) and cycloheximide (similar to 11.4-12.4%). Cocul ture with 10 mu g/mL. bacterial lipopolysaccharide caused a slight fac ilitation of the Mo-induced vasodilation (similar to 78.2-79.6%). Thes e findings suggest that supernatant fluid of rat exuded macrophages cu ltured with low concentrations of L-arginine causes an endogenous nitr ic oxide (NO) and vasodilative prostaglandin dependent relaxation of a rterial smooth muscles.