Abstract

This study was designed to test the hypothesis that the changes in natural killer (NK) cell activity in response to physical exercise were mediated by increased epinephrine concentrations. 8 healthy volunteers 1) exercised on a bicycle ergometer (60 min, 75 VO2max) and 2) on a later day were given epinephrine (EP) intravenously to obtain plasma EP concentrations comparable to those seen during exercise. Blood samples were collected in the basal state, during the last min. of exercise or EP infusion, and 2 h later. The NK cell activity (lysis/fixed number of mononuclear cells) increased during exercise and EP infusion and dropped below basal levels 2 h afterward. The increased NK cell activity during exercise and the EP infusion resulted from an increased concentration of NK (CD16+) cells in the peripheral blood. On the other hand, the decreased NL cell activity demonstrated 2 h after exercise and EP infusion did not simply reflect preferential removal of NK cells from the blood, because the proportion of CD16+ cells was normalized. On the basis of the finding that indomethacin abolished the suppressed NK cell activity in vitro and the demonstration of a twofold increase in the proportion of monocytes (CD14+ cells) 2 h after exercise and EP infusion, we suggest that, after stress, prostaglandins released by monocytes are responsible for downregulation of NK cell function. Our findings support the hypothesis that increased plasma EP during exercise causes a redistribution of mononuclear subpopulations. Verf.-Referat (gekuerzt)