Lipopolysaccharide (LPS) is known to modulate macrophage responses during sepsis including cytokine release, phagocytosis and proliferation. Although agents that elevate cyclic AMP reverse LPS-induced macrophage functions, it is not known whether LPS itself modulates cAMP and whether LPS-induced decreases in proliferation are modulated via a cyclic AMP-dependent pathway. Murine macrophages (ATCC RAW 264.7) were treated with LPS in the presence or absence of inhibitors of prostaglandin signaling, protein kinases, calmodulin, G_i proteins, NF-B translocation or transcription/translation. LPS effects on Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) phosphorylation and the expression of relevant adenylyl cyclase isoforms was measured. LPS caused a significant dose (5-10,000 ng/ml)- and time (1-8 hr)-dependent increase in forskolin-stimulated adenylyl cyclase (AC) activity which was abrogated by pretreatment with SN50 (an NF-B inhibitor), actinomycin D, or cycloheximide, indicating that the effect is mediated via NF-B-dependent transcription and new protein synthesis. Furthermore, LPS decreased the phosphorylation state of CaM kinase II and pretreatment with a calmodulin (CaM) antagonist attenuated the LPS-induced sensitization of AC. LPS, cAMP or protein kinase A activation each independently decreased macrophage proliferation. However, inhibition of NF-B had no effect on LPS-induced decreased proliferation indicating that LPS-induced decreased macrophage proliferation can proceed via PKA-independent signaling pathways. Taken together, these findings indicate that LPS induces sensitization of adenylyl cyclase activity by attenuating the stimulatory effect of calmodulin and the inhibitory effect of CaM kinase II on isoforms of adenylyl cyclase that are calcium/calmodulin sensitive.