ACTH RESPONSE INDUCED IN CAPSAICIN-DESENSITIZED RATS BY INTRAVENOUS-INJECTION OF INTERLEUKIN-1 OR PROSTAGLANDIN-E

1. We investigated whether afferent nerves are involved in the develop ment of adrenocorticotrophic hormone (ACTH) responses induced either b y systemic administration of interleukin-1 beta (IL-1 beta) and prosta glandin E(2), or by psychological stress. The capsaicin desensitizatio n method was used to impair afferent C fibres and we compared the ACTH responses between capsaicin desensitized and vehicle pretreated contr ol rats. 2. The present results showed that the capsaicin desensitized rats had significantly smaller increases in plasma ACTH than the cont rol rats in response to intravenous injection of IL-1 beta or prostagl andin E(2). 3. There were no significant differences between the capsa icin desensitized and control rats in the ACTH responses induced by ca ge switch stress. 4. The capsaicin desensitized rats responded to intr avenous injection of corticotrophin releasing factor (CRF) with a grea ter increase in the plasma level of ACTH than the control rats, indica ting that capsaicin pretreatment resulted in augmentation of pituitary gland sensitivity to CRF. 5. These results suggest that afferent neur ons play an important role in the ACTH responses induced by systemic i njection of IL-1 beta or prostaglandin E(2).