Interleukin-1 increases splenic blood flow by affecting the sympathetic vasoconstrictor tonus

The possibility that interleukin-1 (IL-1), a cytokine involved in immune and inflammatory mechanisms, can affect the blood flow of the spleen was considered because changes in spleen perfusion can affect immune cell recirculation, traffic, and homing. The results indicate that administration of a subpyrogenic dose of IL-1 induced a pronounced increase in splenic blood flow. This was not a general effect, because no change in blood flow of skeletal muscle was noticed. The studies also show that 1) the increase in splenic perfusion induced by IL-1 is to a large extent independent from the secondary induction of nitric oxide (NO), 2) the splenic blood flow in the rat is under sympathetic control, and 3) the effect of IL-1 on splenic blood flow is completely abrogated after surgical interruption of the splenic nerve, which is predominantly composed of sympathetic fibers. It is concluded that the IL-1-mediated increase in splenic blood flow is most likely based on the inhibition of the sympathetic vasoconstrictor tonus in the rat spleen. These results show that a cytokine released by activated immune cells can regulate the blood flow of a main lymphoid organ, the spleen, by affecting mechanisms under neural control.