Relationship between pulmonary embolism, airway obstruction and hypersensitivity of the airways in dogs: influence of partial vagus nerve blockade

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).

[Effects of acetylcholine- and histamine inhalations also of hypoxia on the arterial plasma-histamine concentration (experiments on dogs). III. Communication (author's transl)]

Inhalation of acetylcholine causes increased histamine concentration in the arterial plasma. This increase is smaller than that following allergen inhalation. The increase in Edyn following ACH inhalation may be related to the histamine released to only a very limited extent. Comparison of the effects of histamine inhalation and allergen inhalation on Edyn and plasma histamine concentration leads to the assumption that sensory receptors are located nearer to the surface of the mucosa than that of the mast cells. Hypoxemia is followed by a slight increase in the arterial plasma histamine concentration. The increase in Edyn corresponds to that caused by allergen inhalation although the increase in Edyn and that in the plasma histamine are much smaller.