Wd. Franke et al., EFFECTS OF ALPHA(1)-RECEPTOR BLOCKADE ON THE CARDIOVASCULAR AND THERMOREGULATORY RESPONSES TO SEVERE EXERCISE IN THE HEAT, Journal of Sports Medicine and Physical Fitness, 33(2), 1993, pp. 146-151
Up to an internal temperature of 38-degrees-C, nonacral skin blood flo
w increases with mild exercise in a warm environment. While this appea
rs to be due predominately to an active vasodilator system and not to
altered vasoconstrictor activity, it is uncertain if more intense exer
cise affects this vasodilator response. Consequently, six fit (VO2pk =
62.8 +/- 2.2 ml . kg-1 . min-1, xBAR +/- SEM) college aged men perfor
med 30 min bouts of cycle ergometry exercise at 70% VO2pk in a hot env
ironment (35-degrees-C, 55% rh) while under the influence of either an
alpha1-receptor blocker (prazosin, PRAZ) or a placebo (CTL). Resting
rectal temperature (T(re)) was lower (p = 0.002) and heart rate (HR) h
igher (p = 0.018) during PRAZ. Neither resting nor exercise forearm bl
ood flow (FBF, plethysmography) and forearm vascular conductance (FVC)
differed between PRAZ and CTL. Exercise T(re) and mean skin temperatu
re (T(sk)BAR) did not differ significantly between treatments, rising
to 38.7 and 36.4-degrees-C, respectively, by the 30th min of exercise.
Exercise HR was 4 beats . min-1 higher (p = 0.016) with PRAZ. Mean ar
terial pressure (MAP) did not differ significantly between drug treatm
ents, As FBF, FVC, T(re), T(sk) and MAP were similar between treatment
s while only HR was significantly affected by PRAZ, it appears that al
pha1-receptor blockade does not alter the thermoregulatory responses t
o severe exercise in the heat. However, the elevated HR in the presenc
e of a stable MAP suggests that central venous return may have been at
tenuated during PRAZ.