Journal of Applied Physiology, Vol 58, Issue 3 899-906, Copyright © 1985 by American Physiological Society
Effect of beta-adrenoceptor blockade on thermoregulation during prolonged exercise
N. F. Gordon, P. E. Kruger, J. P. Van Rensburg, A. Van der Linde, A. J. Kielblock and J. F. Cilliers
The effect of clinically used equipotent doses of nonselective (beta 1/beta
2; propranolol) and selective (beta 1; atenolol) beta-adrenoceptor blockers
on thermoregulation was studied during prolonged exercise in the heat. Oral
propranolol (160 mg/day), atenolol (100 mg/day) or matching placebo were
taken for 6 days each by 11 healthy young adult caucasian males. Subjects
participated in 2 h of block-stepping at a work rate of 54 W in an
environmental chamber with a temperature of 33.2 +/- 0.3 degree C dry bulb
and 31.7 /+- 0.3 degree C wet bulb, 2 h after ingestion of the final dose
of each drug. Both active agents produced similar marked (P less than
0.001) increases in subjective perception of effort, the mechanism of which
was not immediately evident from changes in serum electrolytes, blood
glucose, blood lactate, or ventilatory parameters. Propranolol did,
however, cause a greater rise in serum K+ than placebo (P less than 0.02)
and atenolol (P = NS) after exercise. Although rectal and mean skin
temperatures were insignificantly altered by beta-adrenoceptor blockade, an
increased total sweat production was noted with propranolol (P less than
0.01 vs. placebo) and to a lesser degree atenolol (P = NS vs. placebo)
therapy. Analysis of the time course of sweat production showed the
propranolol-mediated enhancement of sweating to ensue largely during the
initial hour of block-stepping and to be transient in nature. The
scientific and clinical implications of this observation will be dependent
upon the precise underlying mechanism, a factor not identified by the
present study.
