INCREASE IN INTRACELLULAR CYCLIC-AMP MODULATES NITRIC-OXIDE PRODUCTION IN IFN-GAMMA-TREATED MACROPHAGES

Macrophages treated with IFN-gamma alone are stimulated to produce nit ric oxide. The level of nitric oxide production can be enhanced signif icantly when IFN-gamma treatment is combined with other agents (e.g., LPS, TNF-alpha, IL-2, etc.). We tested the hypothesis that cAMP plays a role in the IFN-gamma-induced activation of macrophages. Our experim ents indicate that factors that increase the concentration of cAMP in the murine macrophage cell line ANA-1 can also enhance IFN-gamma-induc ed production of nitric oxide. PGE, and cholera toxin increased the pr oduction of nitrite (an indicator of nitric oxide production) in IFN-g amma-treated ANA-1 macrophages by at least twofold. These factors prod uced no increase in nitric Oxide production in the absence of IFN-gamm a treatment. The increase in nitric oxide production corresponded to a n increase in the accumulation of nitric oxide synthase mRNA without a change in stability of mRNA: Dibutyryl cAMP and Sp-cAMPs (a selective activator of cAMP-dependent protein kinase I and II) also increased n itric oxide production in IFN-gamma-treated macrophages. However, at v ery high concentrations (i.e., >100 mu M), the stimulatory effect was decreased. These studies indicate that elevation of intracellular cAMP causes a dose-dependent, biphasic alteration of IFN-gamma-induced nit ric oxide production in murine macrophages. Moreover, they suggest tha t agents that affect nitric oxide synthesis may do so via modulation o f the cAMP second messenger system.