Inhibitory effect of PACAP-38 on acute neurogenic and non-neurogenic inflammatory processes in the rat

Inhibitory actions of pituitary adenylate cyclase activating polypeptide (PACAP) have been described on cellular/vascular inflammatory components, but there are few data concerning its role in neurogenic inflammation. In this study we measured PACAP-like immunoreactivity with radioimmunoassay in the rat plasma and showed a two-fold elevation in response to systemic stimulation of capsaicin-sensitive sensory nerves by resiniferatoxin, but not after local excitation of cutaneous afferents. Neurogenic plasma extravasation in the plantar skin induced by intraplantar capsaicin or resiniferatoxin, as well as carrageenan-induced paw edema were significantly diminished by intraperitoneal PACAP-38. In summary, these results demonstrate that PACAP is released from activated capsaicin-sensitive afferents into the systemic circulation. It diminishes acute pure neurogenic and mixed-type inflammatory reactions via inhibiting pro-inflammatory mediator release and/or by acting at post-junctional targets on the vascular endothelium.