Abstract
Bronchial hyperreactivity to nonspecific bronchoconstrictor stimuli is one of the diagnostic features of asthma. In the present investigation we attempted to determine whether various bronchoactive agents act on bronchoconstriction induced by vagosympathetic nerve stimulation.
We anesthetized 32 young mongrel dogs, weighing 7 to 10kg, with sodium pentobarbital (25mg/kg), paralyzed the respiratory muscles with succinylcholine, and ventilated the lungs through a tracheal cannula at a constant tidal volume (150-250ml) and a frequency of 16/min. Catheters were inserted into the left femoral artery and vein, and measurement of systemic arterial blood pressure (Psyst) and transfusion or infusion of drugs were conducted, respectively. The pressure transducer catheter was connected to the orifice of the tracheal cannula to monitor tracheal pressure (Ptr). The right side vagosympathetic nerve was isolated at the level of thyroid cartilage. We stimulated the cervical vagosympathetic nerve electrically with 5-25V from a square-wave stimulator (ME-6052); pulse duration was lms and the frequencies were 30shocks/s.
1) Percent change of Ptr showed a maked increase by increasing stimulation voltage and reached a plateau at 15 V.
2) Percent change of Ptr induced by vagosympathetic nerve stimulation showed a marked increase 5min after intravenous infusion of neostigmine bromide, and thereafter it showed a gradual decrease and returned to the control level after 75min.
3) Percent change of Ptr induced by vagosympathetic nerve stimulation showed a significant increase with continuous infusion of PGF2α, serotonin, histamine, Tx B2, LT C4 and LT D4.
4) Percent change of Ptr induced by vagosympathetic nerve stimulation showed a significant decrease with continuous infusion of isoproterenol, PGE2, 6-keto PGF1α and aminophylline.
5) Percent change of Ptr induced by vagosympathetic nerve stimulation ahowed a marked increase after pretreatment with propranolol dose-dependently, and reached a plateau at the dose of 600μg/kg.
6) Percent change of Ptr induced by vagosympathetic nerve stimulation showed a significant increase after pretreatment with propranolol and showed a significant decrease after pretreatment with phenoxybenzamine.
The above results suggest that bronchoconstrictor responses induced by vagosympathetic nerve stimulation were modulated by various vasoactive substances.
