DILATATION OF CEREBRAL ARTERIOLES IN RESPONSE TO LIPOPOLYSACCHARIDE IN-VIVO

Background and Purpose Bacterial lipopolysaccharide can increase nitric oxide (NO) production by expression of an inducible form of NO synthase. Bacterial infections of the central nervous system dilate cerebral vessels and increase blood flow. We hypothesized that topical application of bacte rial lipopolysaccharide would increase production of NO, causing dilatation of cerebral arterioles. Methods Cranial windows were implanted in anesthetized rabbits. Windows were flushed with artificial cerebrospinal fluid, artificial cerebrospinal fluid with lipopolysaccharide, or artificial cerebrospinal fluid with lipopolysaccharide and N-G monomethyl-L-arginine (an inhibitor of NO synthase) for 4 hours. Other rabbits received either dexamethasone or indomethacin intravenously 1 hour before lipopolysaccharide treatment of cranial windows. Results Application of lipopolysaccharide in cranial windows produced marked, progressive vasodilatation, with diameter increased by 58+/-7% (mean+/-SEM) after 4 hours. The cerebral vasodilator response was inhibited by N-G-monomethyl-L-arginine, dexamethasone, or indomethacin. Excess L-arginine reversed the inhibitory effect of N-G-monomethyl-L-arginine. Conclusions Inhibition of lipopolysaccharide-induced di latation of cerebral arterioles by N-G-monomethyl-L-arginine and dexamethasone suggests that a portion of the vasodilatation was mediated by inducible NO synthase. Indomethacin also inhibited lipopolysaccharide-induced vasodilatation. These findings suggest an important role for both nitric oxide and cyclooxygenase products in lipopolysaccharide-induced cerebral arteriolar dilatation in vivo.