Central administration of interleukin-1 beta increases norepinephrine turnover in the spleen

We have previously shown that intracerebroventricular (ICV) injection of interleukin-1 beta (IL-1 beta) suppressed splenic macrophage function. Sympathetic noradrenergic innervation of the spleen was implicated as a mediator of this IL-1 beta signal as surgical sympathectomy ablated the macrophage suppression. In this study, we have determined whether ICV administration of IL-1 beta has an effect on sympathetic outflow and norepinephrine (NE) turnover in the spleen. Adult male rats were injected with 5 ng of IL-1 or saline, and NE turnover in the spleen was determined using the rate of decline of NE content in the spleen after synthesis inhibition. The splenic NE turnover rate was increased significantly from 69.52 ng/g/h in saline-treated animals to 111.05 ng/g/h in IL-1-treated animals. In addition, serum corticosterone and ACTH were significantly elevated in IL-1 beta-treated animals 4 h postinjection. These data indicate that central administration of IL-1 beta increases both sympathetic outflow to the spleen and activates the hypothalamic-pituitary-adrenal axis during the period when IL-1 beta induces immunosuppression.