The effect of varying doses of purified human interleukin 1 (IL-1) on rectal temperature (Tr), hypothalamic corticotropin-releasing hormone (CRH), pituitary and plasma adrenocorticotropic hormone (ACTH), and plamsa corticosterone was examined in intact male rats at 24 degrees C; plasma ACTH and corticosterone responses were also studied in hypophysectomized rats. In addition, IL-1-induced changes in corticosterone concentration were investigated by means of adrenal organ cultures. Tr was measured with thermocouples. CRH and ACTH levels were determined by radioimmunoassay, and corticosterone by protein-binding assay. Intravenous administration of IL-1 (0.063-1.0 ng) resulted in hyperthermia, which began 20 min postinjection and continued for an additional 30 min. IL-1 at a dose of 0.5 ng resulted in no change in hypothalamic CRH, pituitary ACTH, or plasma ACTH levels compared with saline-treated rats. Plasma corticosterone was significantly (P less than 0.05) elevated 30 min after IL-1 administration and returned to control levels after 1 h. The higher dose of IL-1 (1.0 ng) did not affect hypothalamic CRH content, but pituitary ACTH began to rise at 15 min and was significantly (P less than 0.05) elevated 30 min after injection. Rats receiving this dose displayed elevated (P less than 0.05) plasma ACTH and corticosterone levels 30 and 60 min postinjection. No change in plasma corticosterone was observed in hypophysectomized rats administered either 1 ng of IL-1 or 1 microgram of recombinant IL-1 beta (rIL-1 beta); adrenal organ cultures treated with IL-1 (10(-11) M) responded similarly.(ABSTRACT TRUNCATED AT 250 WORDS)