Fig. 2
From: Role of vasoactive intestinal peptide in osteoarthritis
Positive role of VIP in osteoarthritis pathogenesis. VIP is released into OA knee joints and subsequent accumulation of VIP in the joint down-regulates the VPAC receptor. Up-regulation of VIP increases the production of pro-inflammatory cytokines which in turn sensitizes afferent nerve fibres leading to the vascular dysfunction and degenerative changes in OA [37, 38, 40]