The changes in pulmonary C-fiber activity and lung mechanics induced by vagal stimulation in rabbits

The effect of unilateral stimulation of the vagus nerve on pulmonary C-fiber activity, total lung resistance (R(L)) and dynamic lung compliance (Cdyn) was studied in anesthetized, artificially ventilated rabbits. Vagal stimulation (4-30 Hz) increased both pulmonary C-fiber activity and R(L) but decreased Cdyn, and these changes were frequency-dependent. Atropine (2 mg/kg) blocked the responses of pulmonary C-fiber, R(L) and Cdyn to vagal stimulation at 4-30 Hz. Stimulation of pulmonary C-fiber activity by the higher volume-induced lung inflation was not significantly altered by atropine (2 mg/kg). A selective SP antagonist [D-Pro2, D-Try(7,9)]-SP (0.5 mg/kg) inhibited bronchoconstrictor responses to vagal stimulation at 30 Hz but had no significant effect on those to the stimulation at 4-17 Hz. These results suggest that excitation of the rabbit pulmonary C-fiber activity by unilateral vagus nerve stimulation would occur as a result of the mechanical stimuli via a cholinergic neurotransmission and that during the stimulation at 30 Hz this excitation partly involves the local release of substance P (SP) to promote acetylcholine outflow.