Fig. 2
a Representative recording showing the effect of 10−6 M VIP on 10−6 M PE pre-contracted in the presence of l-NAME in EI rings (n = 6). b Representative recording showing the effect of 10−6 M VIP on 10−6 M PE pre-contracted in the presence of l-NAME in ED rings (n = 5). c In comparison to the EI control group, a treatment of the EI rings with 10−4 M l-NAME produced significantly smaller relaxation. d In comparison to the control ED group, similarly, treatment with 10−4 M l-NAME also diminished relaxation induced by VIP. Responses are expressed as percentage of the active tension originally generated by 10−6 M PE. Data were expressed as mean ± SE. *P < 0.05; **P < 0.01 versus control group