[Seasonal changes in the thrombocyte aggregation activity of rats]

The seasonal variations of platelet functional activity were studied in normal rats and those under stress. A decrease of intensity of ADP-induced platelet aggregation was shown in autumn-winter season. In rats under stress the seasonal fluctuations of aggregation activity were fless obvious. The analysis of data on seasonal rhythms of hormones determining internal mechanisms of circannual biorhythms and their influences on platelet aggregation activity suggested that the decrease fo platelet aggregation activity in autumn-winter period was due to an increasing amount of thyroid hormones.