EFFECTS OF NITRIC OXIDE SYNTHASE INHIBITION IN LUNG FUNCTION DURING EXERCISE IN ASTHMATICS

Abstract

Upon cessation of exercise, pulmonary resistance (RL) and forced expired volume in one second (FEV1) significantly deteriorate in individuals with exercise-induced asthma. However, lung function during exercise is relatively well preserved. Nitric oxide (NO) is a known bronchodilator that might have a protective effect during exercise. METHODS We evaluated changes in RL during 20 min moderate intensity exercise in 17 subjects with FEV1 91% ± 16% predicted and a positive exercise challenge test (reduction in FEV1>15% after exercise breathing dry air). RL was assessed before, during, and up to 15 min after the 20-min exercise on two days; subjects were treated with a nebulized NO synthase inhibitor LNMMA (Ng-monomethyl-L-arginine, 50mg in 2mL saline) or saline in random order, double blinded. RESULTS LNMMA increased RL (81% ± 78% on LNMMA day vs 6.6% ± 28% on saline day, P < 0.01). A decline in RL early in exercise was not prevented by LNMMA, and post exercise increase in RL was similar on the two days (table). There was a slow rise in RL during exercise that was the same on the two days (0.061 ± 0.063 for saline, 0.078 ± 0.078 for LNMMA, units cmH2O/L/sec per min of exercise).TableCONCLUSIONS Our results suggest that NO might regulate baseline airway tone, but it is not further involved in the control of airway function during or after exercise. A dilator influence is present early in exercise, which might be related to mechanical effect of increased tidal volume or respiratory rate. Supported by NIH grants HL52230 and NIH RR-00585