VIP and constipation disorder: For inhibitory neurotransmitters, the levels of VIP (233.81 ± 5.26 ng/L) and ET (198.98 ± 4.36 ng/L) in the serum of constipation mice were increased compared with normal mice (VIP 207.16 ± 6.12 ng/L, ET 167.87 ± 4.57 ng/L).