Macrophage-induced nitric oxide and prostanoid dependent relaxation of arterial smooth muscles

We have studied mechanisms of vasodilation induced by supernatant fluid of rat macrophages (Mø), using an arterial bioassay preparation. The cells emigrated by an intraperitoneal injection of thioglycollate were 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 demonstrated Wright's esterase staining and phagocytosis of acetylated low-density lipoprotein. The bioassay preparation was made of dog isolated femoral arteries with and without the endothelium. The supernatant of macrophages cultured in the L-arginine-free RPMI 1640 caused a significant reduction of the precontraction in the bioassay rings, being approximately 51.6-66.7% of sodium nitroprusside (SNP) induced maximum vasodilation in each ring. The supernatant of macrophages cultured in the RPMI 1640 containing 2.0 mM L-arginine produced a significantly smaller relaxation (approximately 32.3-33.3%). The Mø-induced vasodilation was significantly inhibited by the coculture of the macrophages with 1 microM dexamethasone, 10 microM cycloheximide, 50 microM N omega-nitro-L-arginine methyl ester (L-NAME), 10 microM indomethacin, or 10 microM aspirin. The L-NAME-induced inhibition was significantly reversed by an additional treatment with 100 microM L-arginine. The coculture with both L-NAME and indomethacin caused a reduction of the Mø-induced vasodilation (approximately 12.5-13.4%) similar to reductions produced by dexamethasone (approximately 10.8-12.1%) and cycloheximide (approximately 11.4-12.4%). Coculture with 10 micrograms/mL bacterial lipopolysaccharide caused a slight facilitation of the Mø-induced vasodilation (approximately 78.2-79.6%). These findings suggest that supernatant fluid of rat exuded macrophages cultured with low concentrations of L-arginine causes an endogenous nitric oxide (NO) and vasodilative prostaglandin dependent relaxation of arterial smooth muscles.