CIRCADIAN VARIATION IN ADRENERGIC RESPONSES IN ASTHMATIC SUBJECTS

Circadian variations in adrenergic responsiveness might underlie nocturnal wheezing in asthma. Cardiovascular, airway and plasma cAMP responses to stepwise infusions of L-adrenaline [epinephrine] (0.01, 0.03 and 0.075 .mu.g/min per kg) at 4 h intervals over 24 h in 5 extrinsic asthmatic men were measured. Peak expiratory flow, blood pressure, heart rate and plasma cAMP showed a significant circadian variation with peak values at 1600 h and trough values at 0400 h. The .beta.2-adrenoceptor-mediated increases in peak flow and cAMP were similar at all times, but adrenergic responsiveness (measured by response/log dose of infused adrenaline) was greater at 0400 h than at 1600 h because of the lower baseline values at night. Blood pressure and heart rate responses to adrenaline infusions did not significantly differ over 24 h. Airway responses to inhaled adrenaline were studied on the 2nd day; the mean peak flow after adrenaline was similar at 1600 h to that at 0400 h and since the pretreatment values were lower at 0400 h, the magnitude of response to inhaled adrenaline was greater at night. There was evidently no significant circadian change in adrenergic responses in asthma and adrenoreceptor dysfunction is apparently not important in the pathogenesis of nocturnal asthma.