Disturbances in pulmonary mechanics during serotonin perfusion

The effect of i.v. perfused serotonin (75 microgram.kg-1.min-1) on bronchomotor tone was assessed in dogs by mechanical studies, with the result in an increase in total lung resistance. The increased residual volume (RV), closing capacity (CC) and slope of phase III (nitrogen single-breath washout) as well as the reduction of the helium response at low lung volumes suggest a peripheral action of the drug. Because of the large increase in total lung resistance and the decreased dead space (VD), bronchoconstriction of large airways must also be present. Vagal tone inhibition is incomplete whether by volume history or bilateral vagotomy and could be limited mainly to a segment which is situated between the equal pressure point and the most peripheral airways: maximal flows during partial expiratory flow-volume manoeuvres (PEFV) are lower than during maximal expiratory flow-volume manoeuvres (MEFV) and the volume of isoflow is higher in PEFV than in MEFV manoeuvers, suggesting that full inspiration reduces the bronchoconstriction induced by serotonin. On the other hand, the bilateral vagotomy did not reverse CC, RV, slope of phase III or VD back to control values. Isoproterenol i.v. injection improved all physiological measurements almost to the level of control values: beta-adrenergic stimulating drugs seem to inhibit completely serotonin induced bronchospasm, at all levels of the bronchial tree.