Dietary salt, airway inflammation, and diffusion capacity in exercise-induced asthma.
OBJECTIVE
Recent studies have supported a role for dietary salt as a modifier of the severity of exercise-induced asthma. The main aim of this study was to demarcate a possible mechanism by which dietary salt modification may alter exercise-induced airway narrowing in asthmatic patients.


METHODS
Twenty-four patients participated in a randomized, double-blind crossover study. Subjects entered the study on their normal salt diet (NSD) and were then placed on either a low-salt diet (LSD) or high-salt diet (HSD) for 2 wk with a 1-wk washout period occurring between diets. Pre- and postexercise spirometry, pulmonary diffusion capacity (DLCO) and its subdivisions, and induced sputum were obtained on the NSD and at the end of each 2-wk treatment period (LSD and HSD).


RESULTS
FEV1 decreased by 7.9 +/- 2.8% on LSD, 18.3 +/- 4.0% on NSD, and 27.4 +/- 3.2% on HSD at 20 min postexercise. The NSD and HSD induced significant reductions (P < 0.05) in DLCO and its subdivisions. However, postexercise pulmonary capillary blood volume significantly increased (P < 0.05) by 6.3 and 9.6 mL on NSD and HSD, respectively, compared with baseline values, with no significant change (P > 0.05) being observed on LSD. Postexercise-induced sputum neutrophil and eosinophil differential cell counts and induced sputum supernatant concentration of eosinophil cationic protein, interleukin (IL)-1beta, IL-8, leukotriene (LT) C(4)-E(4), LTB(4), and prostaglandin D(2) were significantly elevated (P < 0.05) on NSD and HSD compared with LSD.


CONCLUSIONS
Our findings indicate that dietary salt loading enhances airway inflammation following exercise in asthmatic subjects, and that small salt-dependent changes in vascular volume and microvascular pressure might have substantial effects on airway function following exercise in the face of mediator-induced increased vascular permeability.
Mickleborough
Timothy D
TD
Human Performance and Exercise Biochemistry Laboratory, Department of Kinesiology, Indiana University, Bloomington, IN 47401, USA. tmickleb@indiana.edu
Lindley
Martin R
MR
Ray
Shahla
S
D000328:Adult; D001249:Asthma / Q000209:etiology* / Q000503:physiopathology; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007249:Inflammation / Q000209:etiology*; D018836:Inflammation Mediators / Q000032:analysis; D008297:Male; D012123:Pulmonary Ventilation; D017673:Sodium Chloride, Dietary / Q000627:therapeutic use*; D013183:Sputum; D014481:United States
D018836:Inflammation Mediators; D017673:Sodium Chloride, Dietary