ALTERED PLATELET-FUNCTION ASSOCIATED WITH THE BRONCHIAL HYPERRESPONSIVENESS ACCOMPANYING NOCTURNAL ASTHMA

Background: Nocturnal awakening is a common feature of bronchial asthm a, and vet the mechanisms underlying this phenomenon are poorly unders tood. We investigated whether nocturnal awakening is associated with c hanges in platelet function with the use of a variety of markers of pl atelet activation. Methods: Ten patients with a history of nocturnal a sthma and 10 age- and sex-matched healthy control subjects were studie d at 10:00 PM, 4:00 AM, and 10:00 AM on 2 consecutive days. The follow ing parameters were tested: forced expiratory volume in 1 second (FEV1 ), log dose of methacholine inducing a 20% fall in FEV1, platelet coun t and volume, platelet aggregation induced by collagen or activating f actor, and plasma and intraplatelet levels of beta-thromboglobulin and platelet factor 4. Results: We have demonstrated that altered platele t function and platelet activation occurs at 4:00 AM in patients with nocturnal asthma and is associated with the maximum increases in bronc hial reactivity. Such changes were not observed in 10 control subjects . Platelet dysfunction has been detected as a reduced aggregatory resp onse of platelets to collagen and platelet activating factor such that up to 5 times more platelet activating factor and 1.5 times more coll agen were required to elicit a threshold aggregatory response in asthm atic subjects when compared with control subjects; this difference was evident at all time points tested. Furthermore, at 4:00 AM there were significantly lower levels of intraplatelet beta-thromboglobulin corr esponding to the maximum reduction in peak expiratory flow and to the maximal increase in bronchial responses to inhaled methacholine. Concl usions: These results suggest that platelet activation accompanies noc turnal asthma and further suggest that platelets may play a role in th is common clinical condition.