Antigen-induced airway obstruction and the influence of vagus blockade

The role of vagus nerve on histamine- and acetylcholine-induced bronchoconstriction (experiments on cats)

During administration of highly concentrated acetyclcholine and histamine aerosol (20-40 min), different effects on tidal volume, respiratory rate, and bronchial tone could be demonstrated. Inhalation after vagotomy neither showed changes in respiratory rate nor in tidal volume. These results point out the importance of the nervus vagus in case of bronchoconstriction caused by mediators. It is discussed to which degree vagus activity is required for the direct effect of different mediators in living animals.

Role of vagus nerves and inhalative aerosols of acetylcholine and histamine on dynamic pulmonary elastance in anesthetized spontaneously breathing and artificially ventilated dog

The role of the vagus nerves on resting respiratory resistance (R1) and dynamic lung elastance (Edyn) and the mechanism of action of inhaled aerosol of histamine (Hist) and acetylcholine (ACH) were studied in anesthetized spontaneously breathing and artificially ventilated dogs. Observations were also extended to study the effect of electrical stimuli to cut ends of both vagi alone and during inhalation of aerosols. Bilateral cervical vagal blockade by local application of novocaine solution (2.5%) or bilateral vagotomy reduced resting R1 and Edyn and prevented increase of these parameters following inhalation of aerosols of Hist or ACH in spontaneously breathing dogs. However, the similar vagal blockade or vagotomy in artificially ventilated animals showed neither an influence on resting R1 and Edyn nor could it prevent their increase following the exposure to aerosol of Hist or ACH. Electrical stimuli to the peripheral cut ends of vagi induced slight increase in R1 and Edyn, but the effect on heart rate and systemic blood pressure was very strong. The combined effects of aerosol of Hist or ACH and electrical stimuli were additive. It is concluded that inhalation of aerosol of Hist or ACH produced two kinds of effects on respiration: (1) Increased respiratory rates with reduced tidal volume and with bronchoconstriction which were vagus-dependent (spontaneous breathing model), and (2) bronchoconstriction which was a direct response of smooth muscle without involving a reflex (artificial ventilation model).

[Proteolytic lung emphysema and obstructive airway disease (author's transl)]

Inhalation of papain by dogs produced morphological changes corresponding to a centrolobular emphysema. The papain inhalation also induced a purulent catarrhal bronchitis. However, the functional changes seen in chronic obstructive bronchitis were not observed. During papain inhalation an increased sensitivity of the bronchial systems develops corresponding to a tremendous increase in bronchospasm in response to Acetylcholine aerosol. The parenchymal lung tissue in dogs is more vulnerable in developing emphysema after papain exposure than is teh bronchial system in developing a chronic obstructive airway disease.

[The place of attack of beta-2 receptor stimulating bronchodilators. Fenoterol (Berotec) in allergic airway obstruction in dogs, hypersensitive to Ascaris suum]

On dogs sensitive against Ascaris suum extract an increase of the airway resistance can be caused by challenge alone on the upper part or the lower part of the airways by Ascaris suum extract. Fenoterol as beta 2-receptor stimulator is capable to decrease this reaction by deposition of this drug on the upper part as on the lower part of the airways. The effect of Fenoterol on the upper part of the airways is much stronger and lasts much longer than on the lower part of the airways or by intravenous route. A direct effect of the beta 2-receptor stimulator Fenoterol on the sensoric part of the reflex way of the reflex bronchoconstriction must be considered. It will be also discussed that the local application of Fenoterol on the upper part of the airways may influence also the reaction of the bronchial muscles in the lower part of the airways without a direct resorptive-systemic effect. The relationship of these findings for the clinical situation on man has to be investigated.

[Arterial plasma histamine concentration during inhalation of allergen and acetylcholine before and after vagotomy. V. Communication (author's transl)]

In allergic dogs ascaris extract (A.E.) inhalation and, to a less extent, acetylcholine inhalation cause a significant increase in the histamine concentration in the arterial plasma. A.E. and acetylcholine cause a similarly strong increase in Edyn. After bilateral vagotomy A.E. and acetylcholine inhalation entail only a minimal increase in Edyn. The increase in the arterial plasma histamine concentration is as strong as before vagotomy. The results support the assumption that both A.E. and acetylcholine act on the sensory receptors of the reflexway via a reflex mechanism. PO2a decreases as Edyn increases. However, after vagotomy PO2a still decreases significantly although Edyn changes hardly. A.E. and acetylcholine are assumed to have a direct effect on the non-vagus controlled peripheral airways. The peripheral airways are mainly responsible for changes in the arterial blood gases but show no effect on Edyn or airway resistance measurements.