Purpose: The aim of the present study was to assess the effects of two 30-min consecutive exercise bouts on a treadmill at 80% VO2 separated by a 4-h rest interval, on blood cell counts and the production of tissue factor, cytokines, and eicosanoids in lipopolysaccharide (LPS)-stimulated blood. Methods: Blood samples were taken from eight endurance athletes (mean +/- SD: age, 23.4 +/- 1.6 yr; [latin capital V with dot above]O2, 66.0 +/- 6.4 L/minkg, both immediately before and after each exercise bout. Cell counts were performed, and the heparinized blood was subjected to LPS-stimulation for 2 h. Results: There was a significant rise in white blood cell counts after the first exercise bout (81%, P < 0.001), increasing to 123% (P < 0.001) after the second bout. After the first and second runs, the tissue factor activity in LPS-stimulated monocytes was enhanced by 70% (not significant) and almost 200% (P = 0.012), respectively, compared with baseline values. The high monocyte responsiveness after the second bout remained undiminished 2 h later. Similarly, the interleukin (IL)-8 production had risen 70% (P = 0.022) after the first run and 100% (P = 0.005) after the second run, relative to baseline values. IL-6 or leukotriene B4 levels did not change significantly. The rise in LPS-induced thromboxane B2 was 80% (P = 0.024) after the first run and 63% after the second run (P = 0.071, not significant). VO2 correlated negatively with the concentration of granulocytes immediately after the second exercise bout (R = 0.864, P = 0.006). Conclusions: The results of this study are evidence that two physical exercise bouts separated by a 4-h rest are associated with an enhanced propensity of the blood cells to generate tissue factor activity and some proinflammatory products compared with one exercise bout.
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