Regulation of Interleukin-6 (IL-6) production in bone marrow (BM)-derived stromal cells by neuropeptides, pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP), was examined. Both forms of PACAP, PACAP-27 and PACAP-38, as well as VIP significantly increased IL-6 production by rat BM-derived stromal cells at physiological concentrations ranging from 10(-10)-10(-8) M. The three related peptides (PACAP-27, -38, and VIP) stimulated the production of both cAMP and inositol 1,4,5-trisphosphate (IP3) in rat BM-derived stromal cells with similar 50% effective concentrations. The stimulatory potency of the three related peptides for the production of IL-6, cAMP, and IP3 was almost consistent, suggesting that the dual signaling transduction pathways may be involved in PACAP/VIP-induced IL-6 production in rat BM-derived stromal cells. The messenger RNA (mRNA) for the third subtype of PACAP receptor (PVR3) was found to be abundantly expressed in both BM-derived stromal cells and the BM tissue, whereas little of the mRNA for type 1 (PVR1) nor type 2 (PVR2) was detected. Furthermore, the mRNAs for PACAP and VIP were detected in the BM tissue, suggesting that both PACAP/VIP and PVR3 are synthesized in vivo in the BM. The results shown in this paper suggest that PACAP/VIP and their receptor play an important role in the IL-6 production and perhaps in the hematopoiesis in the BM.