Anti-asthma drugs and capsaicine-induced microvascular effects in lower airways.

Substance P, capsaicine and bicervical vagal stimulation may increase microvascular permeability to macromolecules in lower airways. In previous studies techniques were employed that could have adversely affected the microvasculature. An atraumatic method of exposing the guinea-pig trachea to constant concentrations of drugs followed by quantitation of the blood-pool (in vivo 99Tcm-labelled erythrocytes) and extravasated macromolecules (Fitc.-dextran) has now been developed. Capsaicine produced marked extravasation of Fitc.-dextran while substance P in the concentration tested merely had vasodilator properties. Pretreatment with lidocaine, the beta-receptor agonist, terbutaline, or the adenosine non-blocking xanthine, enprofylline, inhibited the capsaicine induced inflammatory response.