Abstract des Autors

Up to an internal temperature of 38 deg C, nonacral skin blood flow increases with mild exercise in a warm environment. While this appears to be due predominately to an active vasodilator system and not to altered vasoconstrictor activity, it is uncertain if more intense exercise affects this vasodilator response. Consequently, six fit college aged men performed 30 min bouts of cycle ergometry exercise at 70% VO2pk in a hot environment (35 deg C, 55% rh) while under the influence of either an alpha 1-receptor blocker (prazosin, PRAZ) or a placebo (CTL). Resting rectal temperature (Tre) was lower and heart rate (HR) higher during PRAZ. Neither resting nor exercise forearm blood flow (FBF, plethysmography) and forearm vascular conducance (FVC) differed between PRAZ and CTL. Exercise Tre and mean skin temperature (Tsk) did not differ significantly between treatments. Exercise HR was 4 beats/min higher with PRAZ. Mean arterial pressure (MAP) did not differ significantly between drug treatments. As FBF, FVC, Tre, Tsk and MAP were similar between treatments while only HR was significantly affected by PRAZ, it appears that alpha1-receptor blockade does not alter the thermoregulatory responses to severe exercise in the heat. However, the elevated HR in the presence of a stable MAP suggests that central venous return may have been attenuated during PRAZ. Verf.-Referat