Effect of beta-adrenoceptor blockade on thermoregulation during prolonged exercise

Abstract

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.

Effect of Beta-Adrenoceptor Blockade and Calcium Antagonism, Alone and in Combination, on Thermoregulation During Prolonged Exercise*

“…In agreement with earlier investigations, beta1 -selective and nonselective beta-adrenoceptor blockade did not alter the rectal temperature rise during exercise in this study (5,9). In contrast, both propranolol and its combination with nifedipine, but not atenolol or its combination with nifedipine, accentuated sweat production.…”

“…by alleviating certain side effects (13). However, despite the increasing participation of many of these same patients in endurance training programs (8,17,19) coupled with the potential detrimental effects of these drugs on temperature control mechanisms (9,10,20), the effect of calcium antagonism, alone or in combination with beta-adrenoceptor blockade, on thermoregulatory responses to prolonged exercise has yet to be investigated. Moreover, the interaction between beta1 -selective and nonselective betaadrenoceptor blockade and thermoregulation is presently poorly understood (9,10,21).…”

“…However, despite the increasing participation of many of these same patients in endurance training programs (8,17,19) coupled with the potential detrimental effects of these drugs on temperature control mechanisms (9,10,20), the effect of calcium antagonism, alone or in combination with beta-adrenoceptor blockade, on thermoregulatory responses to prolonged exercise has yet to be investigated. Moreover, the interaction between beta1 -selective and nonselective betaadrenoceptor blockade and thermoregulation is presently poorly understood (9,10,21). Therefore, the purpose of this study was to establish the effects of the calcium antagonist, nifedipine, when administered alone and in combination with beta-adrenoceptor blockade on thermoregulation during prolonged exercise and to further clarify the thermoregulatory responses induced by beta1-selective and nonselective beta-adrenoceptor blockade.…”

Cardiac Response to Exercise in Health and Disease

“…Controversy surrounds the issue of sweat loss induced by exercise and influenced by prop and aten. [106][107][108] It has been shown that β 1 selective blockers produce less pertubation in thermoregu-lation than do nonselective antagonists. [106][107][108] This is a result of less peripheral vasoconstriction pro ducing less impairment to the sweating mechanism or higher sweat rate with drugs such as atenolol or metoprolol.…”

“…[106][107][108] It has been shown that β 1 selective blockers produce less pertubation in thermoregu-lation than do nonselective antagonists. [106][107][108] This is a result of less peripheral vasoconstriction pro ducing less impairment to the sweating mechanism or higher sweat rate with drugs such as atenolol or metoprolol. Finally, in addition to the above meta bolic changes no one β-antagonist is preferentially better in terms of altering serum lipids when exer cise and β-blockers are combined, 109,110 although selective β blockers do not blunt exercise-induced lipolysis as readily as does propanolol.…”