A nitric oxide (NO) synthase (NOS) can be induced in both astrocytes and cerebral endothelial cells with a combination of interleukin-1 beta/interferon-gamma or lipopolysaccharide/interferon-gamma, respectively. Exogenous NO, either from the chemical donor spermine NONOate or from activated astrocytes, affected the expression of inducible NOS in cerebral endothelial cells. In cerebral endothelial cells pretreated with spermine NONOate the induction of NOS was reduced, as revealed by mRNA expression and nitrite accumulation. Cytokine-treated astrocytes generating NO and placed in close proximity to endothelial cells decreased the expression of NOS induced by cytokines in endothelial cells. In addition, it was apparent that cytokine-activated astrocytes released a factor(s) that initiated transcriptional induction of NOS in cerebral endothelium. This suggests that astrocytes activated by cytokines in vivo could influence expression of inducible NOS in cells of the adjacent microvasculature.