VIRAL-INFECTION POTENTIATES THE INCREASE IN AIRWAY BLOOD-FLOW PRODUCED BY SUBSTANCE-P

We examined the effect of respiratory tract infection with Sendai viru s on the responsiveness of airway blood flow to substance P (SP) in ra ts. Pathogen-free rats were inoculated with either Sendai virus suspen sion or sterile viral growth medium into each nostril. Five days later , we measured airway and esophageal blood flows before and immediately after injection of SP or histamine into the left ventricle of rats in both groups using a modification of the reference-sample microsphere technique. Viral infection potentiated the increase in airway blood fl ow evoked by SP but not by histamine. We also examined the effect of n eutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE) on the SP-induced increase in airway blood flow. Both phosphoramidon (NEP inhibitor) and captopril (ACE inhibitor) potentiated the increase in airway blood flow produced by SP in pathogen-free rats. In the presenc e of both peptidase inhibitors, a submaximal dose of SP increased bloo d flow to a similar level in infected and pathogen-free rats. Thus dec reased activity of both ACE and NEP may be involved in the exaggerated increase in airway blood flow evoked by SP in virus-infected rats.