Leu‐enkephalin induced by IL‐2 administration mediates analgesic effect of IL‐2

&NA; Interleukin‐2 (IL‐2) was found to have an analgesic effect in both central and peripheral nervous systems. This effect is related to opioid receptors and mediated mainly by IL‐2 directly binding to opioid receptors. Using radioimmunoassay, the content of Leu‐enkephalin (LEK) in some nuclei were measured at intervals after the injection of IL‐2 into the lateral ventricle of rats. Levels of LEK increased in both paraventricular hypothalamic nucleus (PVN) and locus ceruleus (LOC) after IL‐2 admistration, suggesting that the analgesic effect of IL‐2 is also related to the change of LEK in PVN and LOC induced by IL‐2 administration.