NONCHOLINERGIC, NONADRENERGIC BRONCHODILATION IN THE CAT

Publisher Summary This chapter focuses on noncholinergic, nonadrenergic bronchodilation in the cat. The study described in the chapter investigated the possibility of a purine being the neural transmitter with an in vivo version of the isolated smooth muscle preparation. Cats were anesthetized with chloralose–urethane and were intubated, paralyzed, and artificially ventilated. The tone of the smooth muscle was assessed by the measurement of pulmonary resistance with a forced oscillation technique. The animals were then treated with atropine and propranolol. The cats were bronchoconstricted with serotonin which elevated airway tone, such that pulmonary resistance increased five- to tenfold. Stimulation of the parasympathetic branch of the vagus nerve resulted in reproducible bronchodilation. Adenosine (AD) or ATP in logarithmically increasing concentrations were then either injected or aerosolized into the cat. However, neither purine had a discernable effect on pulmonary resistance. Quinidine or aminophylline were then infused until the bronchodilation induced by electrical stimulation appeared to be blocked. Both agents blocked the effects of electrical stimulation, with quinidine blocking at a total dose of 30 mg/kg and aminophylline blocking at 70 mg/kg. However, not only were these dose levels in the toxic range but the results were also consistent with the known deterious effects that both agents have on neural transmission.