THE EFFECT OF ACUTE VS CHRONIC TREATMENT WITH BETA-ADRENOCEPTOR BLOCKADE ON EXERCISE PERFORMANCE, HEMODYNAMIC AND METABOLIC PARAMETERS IN HEALTHY-MEN AND WOMEN

1 Variable results have been reported on the effect of beta-adrenocept or blockers on maximal oxygen uptake (VO2 max) and exercise endurance. This may in part be due to different subject populations, but it coul d also be due to an adaption of metabolic and haemodynamic responses t o exercise during chronic treatment with beta-adrenoceptor blockers. T he present study was therefore carried out to examine the effect of ac ute and chronic administration of the non-selective beta-adrenoceptor blocker propranolol on both peak VO2 and exercise performance in the s ame subjects. Since the effect of beta-adrenoceptor blockade has not b een properly investigated in women, eight healthy women were compared with seven men. Progressive bicycle exercise to exhaustion was perform ed after propranolol 0.15 mg kg(-1) i.v. (acute) or 80 mg three times daily for 2 weeks (chronic) or placebo given according to a double-bli nd crossover design. 2 Mean (s.e. mean) peak VO2, was significantly re duced from 42.3 (1.6)ml min(-1)kg(-1) during placebo to 40.3 (1.2, P<0 .05) ml min(-1)kg(-1) after acute and 39.1 (1.2, P<0.001)ml min(-1)kg( -1) after chronic propranolol treatment. No significant difference in peak VO2, between the two propranolol treatment regimens was observed (mean difference 1.2, 95% CI -0.1 to 2.4ml min(-1) kg(-1)). There was no treatment interaction with gender. 3 Cumulative work, 163 (9.3)kJ, was significantly reduced by acute, 148 (7.7, P < 0.001) kJ, and chron ic, 147 (7.6, P < 0.001) kJ, administration of propranolol since the t ime to exhaustion was reduced by 5.3% and 5.3%, respectively. There wa s no significant difference between the two regimens of propranolol (m ean difference 0.2, 95% CI -6.7 to 7.0 kJ) or between the sexes. Maxim al knee extensor and handgrip strengths were not affected by propranol ol. 4 Whereas sex did not influence ventilatory, haemodynamic or metab olic parameters, some differences were observed between acute and chro nic propranolol treatment During submaximal exercise oxygen uptake was reduced by approximately 2% and RER values increased by 0.04-0.05 aft er chronic treatment in contrast to no effect of acute propranolol tre atment. Heart rate and systolic blood pressure were reduced significan tly more after chronic compared with acute propranolol treatment; peak heart rate being 186 (2.2), 147 (2.3) and 134 (2.3) beats min(-1), an d peak systolic blood pressure being 189 (7), 171 (4) and 161 (4) mmHg after placebo, acute and chronic propranolol administration, respecti vely. Also the exercise induced rise in potassium and lactate levels w ere modified differentially; the rise in potassium concentration was l ess after chronic compared with acute propranolol treatment and lactat e levels were reduced only after chronic administration of propranolol . In contrast, ventilation, which was unchanged after propranolol duri ng submaximalexercise, was reduced to similar extent at exhaustion fro m 108 (6.4) to 97 (7.2) and 96 (5.9)1 min(-1) after acute and chronic propranolol administration, respectively. Diastolic blood pressure and subjective perception of fatigue were similar across the treatment re gimens. 5 The study has demonstrated that acute and chronic administra tion of propranolol result in different haemodynamic and metabolic res ponse to exercise, although endurance and peak oxygen consumption were reduced to the same extent. The response to propranolol was not signi ficantly different between men and women.