Exercise refractoriness after histamine inhalation in asthmatic subjects

Area of Science:

• Respiratory Medicine
• Pulmonary Physiology
• Allergy and Immunology

Background:

• Asthma is characterized by airway hyperresponsiveness to various stimuli.
• Exercise and histamine inhalation are known triggers of bronchoconstriction in individuals with asthma.
• Repeated exposure to these stimuli can lead to reduced airway narrowing, suggesting the involvement of inhibitory mechanisms.

Purpose of the Study:

• To investigate whether prior exposure to exercise or histamine affects the subsequent bronchoconstrictive response to the alternate stimulus in asthmatic subjects.
• To determine the directionality of any cross-refractoriness between exercise and histamine challenges.

Main Methods:

• Eight asthmatic subjects with exercise-induced bronchoconstriction participated in four study days.
• Each day involved two challenges separated by one hour: two exercise challenges, two histamine challenges, or sequential histamine and exercise challenges in either order.
• Lung function, specifically the forced expiratory volume in one second (FEV1) and provocative concentration (PC20) for histamine, was measured.

Main Results:

• Repeated exercise challenges significantly reduced subsequent bronchoconstriction (p<0.005).
• Repeated histamine challenges also significantly reduced airway responsiveness (p<0.005).
• Prior histamine inhalation attenuated exercise-induced bronchoconstriction (p<0.005), but prior exercise did not alter the response to histamine (p<0.5).

Conclusions:

• Histamine inhalation can induce a refractory state against subsequent exercise challenge in asthma, likely via released inhibitory mediators.
• Exercise-induced refractoriness does not extend to histamine challenge, suggesting a unidirectional inhibitory pathway.
• These findings highlight differential mechanisms underlying airway refractoriness to various stimuli in asthma.