Effect of Propranolol and Pindolol on the Up-Regulation of Lymphocytic β Adrenoceptors During Acute Submaximal Physical Exercise. A Placebo-Controlled, Double-Blind Study

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Abstract
The effect of .beta.-adrenoceptor antagonists, with and without intrinsic sympathomimetic activity, on the regulation of lymphocytic .beta. adrenoceptors during acute physical exercise was studied. Seven healthy volunteers underwent a graded maximal ergometer test after treatment for 7 days with placebo, propranolol (2 .times. 80 mg/day), or pindolol (2 .times. 10 mg/day). Each subject received the three types of drug treatment in a double-blind, randomized fashion, with 3 weeks wash-out periods between the on-drug periods. The mean resting density of lymphocytic .beta. adrenoceptors was 46 .+-. 5 fmol/mg protein (mean .+-. SEM) during placebo, 53 .+-. 5 fmol/mg protein during propranolol, and 29 .+-. 4 fmol/mg protein during pindolol treatment (p < 0.05, pindolol vs. propranolol). Exercise induced a significant up-regulation of the .beta.-adrenoceptor density during each treatment modality, but the increment was attenuated during propranolol (mean elevation, 16 .+-. 2 fmol/mg protein, p < 0.05) and pindolol intake (13 .+-. 4 fmol/mg protein, p < 0.02) as compared with the placebo value (56 .+-. 13 fmol/mg protein). Moreover, exercise-induced increment of lymphocytic cyclic AMP (cAMP) production was virtually abolished by the two .beta.-adrenoceptor antagonists. In conclusion, administration of .beta.-adrenoceptor antagonists is associated with a subnormal up-regulation of the lymphocytic .beta.-adrenoceptors and alterations in their functioning during heavy physical effort. This attenuation is not modified by intrinsic sympathomimetic activity of the compound.