Effect of Training on ??1 ??2 ??3 Adrenergic and M2 Muscarinic Receptors in Rat Heart

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Abstract
BARBIER, J., F. RANNOU-BEKONO, J. MARCHAIS, P.-M. BERTHON, P. DELAMARCHE, and F. CARRÉ. Effect of Training on β1 β2 β3 Adrenergic and M2 Muscarinic Receptors in Rat Heart. Med. Sci. Sports Exerc., Vol. 36, No. 6, pp. 949–954, 2004. Objective: Physical training is known to alter several cardiovascular parameters. These adaptations are for a great part linked to an alteration of the myocardial responses to its autonomic nervous regulation. To further explain the parasympathetic and catecholamine effects, we hypothesized that endurance training could modify rat myocardial β1, β2, β3 adrenoreceptors (AR) and M2 muscarinic cholinergic receptor (AchR) densities. Methods: Two groups of adults female Wistar rats were studied: controls (C) (N = 7) and trained (T) (N = 9). An 8-wk treadmill training protocol was performed, 5 d·wk−1 and of 1 h·d−1. At the end of the training session, left ventricle and atria muscle were isolated and weighed. Then, quantification of β1, β2, β3 AR and M2 AchR was performed using Western blot analysis. Results: M2 AchR densities were not modified in left ventricle or in atria by training (respectively, 100 ± 22%, C vs 101 ± 14%, T and 100 ± 23%, C vs 119 ± 30%, T). Concerning the left ventricle β AR isoforms, β1AR density was decreased in T (80 ± 10% T vs 100 ± 14% C, P = 0.01), β2AR was unaltered (102 ± 12%, T vs 100 ± 17%, C), and β3 AR density was increased in T (139 ± 38% T vs 100 ± 15% C; P < 0.05). Conclusions: Our results show for the first time that in female rats an 8-wk treadmill training protocol alters specifically the left ventricle β AR isoforms densities but not the M2 AchR one. These results could explain some of the beneficial cardiovascular adaptations of the physically trained heart.