Changes in erythrocyte deformability during day and possible role of melatonin

Objectives. The deformability of erythrocytes is their ability to change shape in order to pass through the capillaries. Th is is necessary for quality of microcirculation and sufficient delivery of oxygen to the tissues. Th e aim of our study was to investigate the possible spontaneous changes in the erythrocyte deformability during day and evaluation of the possible direct effects of melatonin (hormone involved in regulation of biorhythms) on the erythrocyte deformability. Methods. Samples of capillary blood were taken from 12 healthy volunteers in the morning (8:00) and early in the evening (16:30). Determination of erythrocyte deformability was done based on the measurement of their filtrability. It was measured immediately aft er the sample collection and 2-hour lasting incubation without or with melatonin (2000 μmol/L). Results. Erythrocyte deformability was significantly lower in the morning (filtrability index: 0.68±0.01 morning vs. 0.71±0.01 early evening, p<0.05). Th e incubation of blood samples with melatonin did not have impact on deformability. Conclusions. We suggest the presence of diurnal changes in erythrocyte deformability with worse values in the morning that may contribute to higher risk of ischemic attacks in the morning hours. Direct in vitro effect of melatonin on deformability was not observed, but possible in vivo effects cannot be excluded.