The present study determined the plasma ACTH and corticosterone responses of the rat to acute local inflammation induced by the im injection of a small volume of turpentine. In response to tissue injury, ACTH and corticosterone concentrations rose rapidly, peaked at 1 h, and returned toward basal values by 3 h after turpentine injection. As acute inflammation developed, plasma interleukin-6 bioactivity increased significantly, and ACTH and corticosterone levels exhibited a secondary rise. These secondary responses were maximum 6-12 h after turpentine administration, persisted for 20-28 h, and were statistically significant regardless of the normal circadian variations in ACTH and corticosterone secretion. Injection of neutralizing anti-CRF antiserum 7 h after turpentine produced a complete reversal, whereas antiarginine vasopressin (anti-AVP) caused a partial (approximately 40%) inhibition, of inflammation-induced ACTH secretion. The cyclooxygenase inhibitor, ibuprofen (10 mg/kg, iv), like CRF antiserum, rapidly and completely reversed turpentine-induced ACTH secretion. In contrast, the nitric oxide synthase inhibitor, Nw-nitro-L-arginine methyl ester (30 mg/kg, iv), produced a significant enhancement of the ACTH response within 30 min of its injection. Measurement of plasma interleukin-6 bioactivity and fever showed that neither anti-CRF, anti-AVP, ibuprofen, nor Nw-nitro-L-arginine methyl ester acutely influenced the local inflammatory process itself, suggesting that these agents interacted directly with the hypothalamo-pituitary-adrenal axis. These data demonstrate that the ACTH response to local inflammation is mediated by synergistic actions of CRF and AVP, and that both stimulatory (PGs) and inhibitory (nitric oxide) intermediates regulate this response.