Tachykinins do not cause plasma leakage in the rabbit trachea

The aim of this study was to determine if neuropeptides mediate increases in airway microvascular leakage in the rabbit. New Zealand white rabbits were anaesthetised and challenged with either capsaicin (50 mg/kg s.c. or i.p.) or substance P (10(-3) or 10(-4) nebulised or 1 microgram/kg i.v.) or vagally stimulated with a range of pulse trains (5-15 Hz, 5-15 V, 0.2-2 msec). Microvascular leakage was assessed using the Evans blue dye technique. A further two groups of rabbits were challenged with nebulised metabisulphite (100 mg) or phosphate buffered saline to serve as positive and negative controls. Challenge with capsaicin, substance P or vagal stimulation did not significantly increase tracheal or bronchial Evans blue concentrations above negative control levels. We conclude that neuropeptides do not mediate increases in microvascular leakage in the major airways of the rabbit.