A study was carried out to investigate whether an imbalance in the autonomic nervous system or release of histamine, or both, is responsible for the nocturnal increase in airflow obstruction in asthmatic children. The study comprised 18 children with allergic asthma, nine with (group 1) and nine without (group 2) nocturnal airflow obstruction, and an age matched control group. All drugs were withheld for three days before and during the study. On day 4 each child was admitted to hospital and a series of measurements was made every four hours for 24 hours. These included measurements of the forced expiratory volume in one second (FEV1), heart rate and sinus arrhythmia gap from an electrocardiogram (an indirect measure of parasympathetic activity) and urine sampling for determination of catecholamine and N'-methylhistamine concentrations (measures of sympathetic activity and histamine release respectively). Urinary N'-methylhistamine excretion was significantly higher over the 24 hours in children in group 1 than in children in group 2, and overnight values were also significantly higher in children in group 1 than those in group 2. Mean (SEM) values (mumol/mol creatinine) were 154.6 (11.2) in group 1 and 110 (11.2) in group 2 for 2400-0400 hours samples and 139.2 (13.1) and 101.2 (10.6) 0400-0800 hours samples. There was no evidence of decreased sympathetic or increased parasympathetic activity in association with the nocturnal airflow obstruction; noradrenaline concentrations were increased in group 1. These observations indicate that nocturnal airflow obstruction is associated with increased release of histamine overnight.
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