β-adrenoceptor adaptation to endurance training
Endurance exercise is associated with various cardiovascular adaptations, and these may include changes in sympathoadrenal activity and end-organ responsiveness to norepinephrine (NE). Because (3-adreno-ceptor function is a major determinant of sympathetic responsiveness, we used the lymphocyte p-adrenoceptoras a model to study the effects of endurance training in 19 male subjects before, during, and after preparation for a marathon race. Before the subjects trained, resting βadrenoceptor density was positively correlated to resting heart rate (r = 0.47, p < 0.05) but this correlation was not evident after training. Eleven of the 19 subjects completed the 31/2-month training period, and mean (±1 SD) resting p-adrenoceptor density fell from 1,593 ± 333 to 1,197 ± 332 sites per cell (p < 0.02) after the training period. Two weeks after cessation of training, receptor density was at pretraining values of 1,547 ± 209 sites per cell. During training, the subjects ran two 21-km races. Each of these was associated with decreases in β-adrenoceptor density. Our results demonstrate the episodes of endurance running result in reductions in lymphocyte p-adrenoceptor density. We conclude that down-regulation of p-adrenoceptors is an important component of the response to endurance training. © 1987 Raven Press, Ltd., New York.
Ohman, EM; Butler, J; Kelly, J; Horgan, J; O’Malley, K
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