title: Smokers lack morning increase in platelet sensitivity to nitric oxide.
abstract: This study investigated whether a circadian variation is present in the sensitivity of platelets to nitric oxide (NO) and, if so, if long-term smoking modifies it. Blood samples were taken at 0:00, 6:00, 9:00, 12:00, and 18:00 from 14 nonsmokers and 10 smokers. Dose-response curves for platelet aggregation by collagen were constructed in both the presence and absence of 1.0 micro M of NOR-3, a NO donor. The antiaggregation properties of NOR-3 were quantified by the half maximal concentration (EC50) ratio in the presence of NOR-3 to that in its absence. Platelet aggregation showed a monophasic circadian rhythm, with the lowest levels at 6:00 and the highest at 18:00 in both groups. However, there was a significant (p < 0.01) upward shifting of platelet aggregation in the smokers. A circadian variation in sensitivity to NOR-3 also was demonstrated in the nonsmokers. The sensitivity was lowest at 6:00 (1.68 +/- 0.19), increased significantly at 9:00 (2.58 +/- 0.26; p < 0.01), and remained high at 12:00 (2.47 +/- 0.21; p < 0.05). In smokers, however, a circadian variation in platelet sensitivity to NOR-3 was not found. Furthermore, the sensitivity was significantly lower at 9:00 and 12:00 in smokers (1.94 +/- 0.26 and 1.76 +/- 0.13, respectively; p < 0.05 for both) than in nonsmokers. Thus, long-term smoking impairs the normal morning increase in platelet sensitivity to NO, making platelets in smokers more thrombogenic during the hazardous hours.
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D004837:Epinephrine / Q000097:blood; D006801:Humans; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009638:Norepinephrine / Q000097:blood; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D012907:Smoking / Q000097:blood*
chemical_list: D020030:Nitric Oxide Donors; D009569:Nitric Oxide; D009638:Norepinephrine; D004837:Epinephrine