Circadian variation of white blood cell aggregation and free radical indices in men with ischaemic heart disease

The fibrinolytic activity of blood has a circadian variation with increased thrombotic tendency in the morning. This may be a contributory factor to the circadian variation in the time of onset of thrombotic events. However, there has recently been increasing interest to the role of the white blood cells (WBC)and free radicals (FRs) in thrombosis. We have previously reported a circadian variation in WBC aggregation and FR status in normal volunteers. No one has yet studied possible circadian variations in these parameters in patients with stable ischaemic heart disease (IHD).

Ten men with stable IHD had blood samples collected at four-hourly intervals from midday until midday the following day. The patients were ambulant until midnight at which time they went to bed and remained in bed until 0800 h. The following were measured on each sample: WBC aggregation, malondialdehvde (MDA) which is a product of lipid peroxidation by FRs; the FR scavengers, plasma thiol (PSH), red cell glutathione (GSH) and superoxide dismutase (SOD) which are all altered in the presence of increased FR activity. WBC aggregation and PSH had significant circadian variations, P < 0·015 and P<0·001 respectively. The WBC aggregation peak was at 1200 h and trough at 1600 h, the PSH peak was at midnight and the trough at 0400 h.

WBC behaviour and FR status influence the flow properties of blood. The largest rise in WBC aggregation occurredfrom 0800 h to 1200 h; such an increase in aggregation could predispose to microcirculatory occlusion. The level of the scavenger PSH was lowest at 0400 h; at this time FR products, as measured by MDA in the IHD patients, did not fall. This is in contrast to normal volunteers. This combination of low level of plasma scavenger and a relatively raised MDA level may predispose to thrombosis at this time.