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1 Laboratoire "réponses cellulaires et fonctionnelles à l'hypoxie" EA 2363, Association pour la Recherche en Physiologie de l'Environnement, Université Paris XIII, 93017 Bobigny, France; and 2 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160-7401
Chronic hypoxic
exposure results in elevated sympathetic activity leading to
downregulation of myocardial
1- and
-adrenoceptors (
1-AR,
-AR). On the other hand, it has been shown
that sympathetic activity is reduced by exercise training. The
objective of this study was to determine whether exercise training
could modify the changes in receptor expression associated with
acclimatization. Four groups of rats were studied: normoxic sedentary
rats (NS), rats living and training in normoxia (NTN), sedentary rats
living in hypoxia (HS, inspired PO2 = 110 Torr), and rats living and training in hypoxia (HTH, inspired
PO2 = 110 Torr). Training consisted of
running in a treadmill at 80% of maximal O2 uptake during
10 wk. Myocardial receptor density was measured by radioactive ligand binding. Right ventricular (RV) hypertrophy occurred in HS but not in
HTH. No effect of exercise was detected in RV weight of normoxic rats.
Acclimatization to hypoxia (HS vs. NS) resulted in a decrease in both
1- and
-AR density, whereas muscarinic receptor
(M-Ach) expression increased. Hypoxic exercise training (HS vs. HTH)
moderated
-AR downregulation and M-Ach upregulation and prevented
the fall in
1-AR density. Normoxic training (NS vs. NTN) did not change
-AR density. On the other hand, densities of
1-AR in both ventricles as well as RV M-Ach increased in
NTN vs. NS. The data show that exercise training in hypoxia
1) prevents RV hypertrophy, 2) suppresses the
downregulation of
1-AR in the left ventricle (LV) and
RV, and 3) attenuates the changes in both
-AR and M-Ach
receptor density in LV and RV. Exercise training in normoxia increases
M-Ach receptor expression in the RV.
1-adrenoceptor;
-adrenoceptor; M-ACh receptor; right ventricular hypertrophy; moderate hypoxia
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