Effect of bombesin and substance P on the smooth muscle of the chicken crop

The effect of bombesin and of substance P was investigated in smooth muscle strips of the chicken crop. Bombesin in picomolar concentration (0.1×10^-12–5×10^-12mol/l) caused a concentration-related contraction of the muscle strips. Substance P in nanomolar concentration (0.1×10^-9–10×10^-9mol/l) was effective in the same manner. Tetrodotoxin (2×10^-7mol/l) did not influence the contraction responses to either bombesin or substance P. The excitatory effect of bombesin and of substance P did not follow activation of cholinergic receptors since their effect on the crop smooth muscle was not antagonized by atropine (10^-4mol/l) or by hexamethonium (10^-4mol/l). Strips stored for 24 hours in the Tyrode's solution at 4°C without a supply of oxygen maintained their full sensitivity to bombesin and to substance P. These results are consistent with a direct action of bombesin and substance P on the crop smooth muscle.