Central noradrenergic system modulates plasma interleukin-6 production by peripheral interleukin-1

The role of the central noradrenergic system in systemic interleukin-6 (IL-6) production induced by intravenously administered recombinant human interleukin-1 beta (IL-1 beta) was examined in rats. Pretreatment of rats intracerebroventricularly with 6-hydroxydopamine (6-OHDA, 100 or 200 mu g/rat) significantly attenuated the increase in plasma IL-6 levels caused by IL-1 beta (2 mu g/kg iv). A modest inhibition of the IL-1 beta-induced plasma IL-6 production was observed following pretreatment with prazosin (20 mu g/rat icv) but not after administration of idazoxan or propranolol. There were no significant increases in the IL-6 content in the hypothalamus, medulla oblongata, and cortex of the brain after intravenous IL-1 beta. Adrenalectomy produced an augmented plasma IL-6 response to intravenous IL-1 beta, whereas chemical sympathectomy with intraperitoneal injection of 6-OHDA (50 or 100 mg/kg) decreased the IL-lp-induced plasma IL-6 levels. Norepinephrine (NE), in the dose range 10(-6)-10(-4) M, significantly increased the IL-6 levels in the rat spleen lymphocyte culture media. At doses of 10(-9)-10(-7) M, NE enhanced the effect of IL-1 beta on the IL-6 release by spleen lymphocytes in a dose-dependent manner. These findings suggest that the plasma IL-6 response to intravenous IL-1 beta is partially mediated through the activation of the central noradrenergic system and a consequent increase in the sympathetic outflow to the peripheral tissues and that the NE released from the sympathetic terminals may function as a mediator and/or modulator to facilitate the synthesis/release of IL-6 in the sympathetic nerve-innervated organs.