Diurnal variation of lung reactivity in normal and myopathic hamsters

In this study we measured the diurnal variation in lung reactivity in normal and myopathic hamsters. Lung reactivity to an intravenous bolus of 0.7 mg/kg acetylcholine (ACh) was measured as the change in peak airway pressure of anesthetized ventilated animals. In the normal hamsters, lung reactivity was 575% higher during the day (8 A.M., 12 P.M., and 4 P.M.) than during the night (p = 0.01). This increased reactivity was not associated with any changes in baseline pressures. The lung reactivity was correlated to body activity as measured on an electronic activity monitor over seven consecutive days. The hamster, being a nocturnal forager, gradually increased activity at about 6 P.M. and maintained intermittent activity until about 6 A.M. Sleep occurred between 6 A.M. and 6 P.M., and this was when the lung reactivity was greatest. In the myopathic hamsters, although the magnitude of the response to ACh was about 40% lower than that in normal animals, the lung reactivity during the daytime was still about 46% greater than that during the night (p = 0.007). The body activity records from the myopathic animals showed that these animals do not have a normal sleep pattern during the daytime; sleep is not continuous, showing intermittent periods of physical activity. Our results in the normal animals are consistent with observations in man, which show greater problems with airway obstruction and asthmatic attacks during the night. The results in the myopathic animals, which show a persistent diurnal variation of lung reactivity in the presence of an abnormal sleep pattern, lead to the speculation that the diurnal variation may be related to the light/dark pattern rather than to the rest/activity pattern.