Exercise training alters the effect of chronic hypoxia on myocardial adrenergic and muscarinic receptor number

Chronic hypoxic exposure results in elevated sympathetic activity leading t o downregulation of myocardial alpha (1)- and beta -adrenoceptors (alpha (1 )-AR, beta -AR). On the other hand, it has been shown that sympathetic acti vity is reduced by exercise training. The objective of this study was to de termine whether exercise training could modify the changes in receptor expr ession associated with acclimatization. Four groups of rats were studied: n ormoxic sedentary rats (NS), rats living and training in normoxia (NTN), se dentary rats living in hypoxia (HS, inspired PO2 = 110 Torr), and rats livi ng and training in hypoxia (HTH, inspired PO2 = 110 Torr). Training consist ed of running in a treadmill at 80% of maximal O-2 uptake during 10 wk. Myo cardial receptor density was measured by radioactive ligand binding. Right ventricular (RV) hypertrophy occurred in HS but not in HTH. No effect of ex ercise was detected in RV weight of normoxic rats. Acclimatization to hypox ia (HS vs. NS) resulted in a decrease in both alpha (1)- and beta -AR densi ty, whereas muscarinic receptor (M-Ach) expression increased. Hypoxic exerc ise training (HS vs. HTH) moderated beta -AR downregulation and M-Ach upreg ulation and prevented the fall in alpha (1)-AR density. Normoxic training ( NS vs. NTN) did not change beta -AR density. On the other hand, densities o f alpha (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 hypertro phy, 2) suppresses the downregulation of alpha (1)-AR in the left ventricle (LV) and RV, and 3) attenuates the changes in both beta -AR and M-Ach rece ptor density in LV and RV. Exercise training in normoxia increases M-Ach re ceptor expression in the RV.