EFFECTS OF EXOGENOUS NOREPINEPHRINE ON VENTILATORY MECHANICS IN RAT

  • 1 January 1978
    • journal article
    • research article
    • Vol. 207  (2) , 381-387
Abstract
The effects of i.v. administration of norepinephrine on ventilatory mechanics were assessed in the anesthetized, spontaneously breathing rat. Pulmonary resistance, dynamic compliance and functional residual capacity remained unchanged during a 10-min infusion period. After paralysis, repetition of the norepinephrine infusion caused an increase in static deflation recoil pressure at lung volumes above the tidal range but maximum expiratory flow rates at corresponding lung volumes were not increased indicating an elevation in the resistance of upstream airways. Flow rate responses to low density gas breathing were not enhanced by norepinephrine suggesting peripheral airways narrowing as the cause of the increased upstream resistance. Isoproterenol protected animals against serotonin-induced bronchoconstriction whereas norepinephrine augmented the response to serotonin. In intact rats norepinephrine increases the flow-resistive properties of peripheral airways, does not measureably alter the caliber of central airways and possesses no discernible bronchodilator activity. The effects of norepinephrine on small airways appear to be secondary to changes in pulmonary hemodynamics rather than the result of direct stimulation of .alpha.-adrenoceptors in airway smooth muscle.