Maintenance of muscarinic tone after vagotomy in the lung periphery

We developed a method for maintaining muscarinic tone in a small region of the lung periphery after vagotomy. A fiber-optic bronchoscope was wedged in a segmental airway of anesthetized male mongrel dogs and was used to deliver aerosols of distilled water (0.1 ml), neostigmine (0.022 mg), atropine (0.1 mg), and histamine (1.5 X 10(-4) mg). Measurements of resistance through the collateral system (Rcs) were used to monitor responses to these agents. Rcs increased 37.0 +/- 5.0% (mean +/- SE) after the administration of neostigmine and remained elevated for at least 50 min. The administration of neostigmine in vagotomized animals or in those where the obstructed lung segment was pretreated with atropine resulted in a small increase in Rcs that lasted only 2 min. When bilateral vagotomy was performed 10 min after neostigmine administration Rcs remained elevated for at least another 80 min. However, Rcs returned to baseline when atropine was administered 20 min after vagotomy, but increased when histamine was administered 50 min after atropine. We conclude that after neostigmine administration, parasympathetic tone, dependent on mediators released from the vagus nerve, can be maintained in the lung periphery after vagotomy.