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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
The time course of changes in rat myocardial 
1-
and 
-adrenoceptors and of muscarinic cholinergic (M-Ach)
receptor characteristics was studied parallel with the changes in
exercise systemic O2 transport during a 21-day period of
hypoxia (barometric pressure 380 Torr) to assess the effects of
receptor modification during acclimatization on maximal exercise
capacity. Hypoxia resulted in polycythemia, pulmonary
hypertension, right ventricular hypertrophy, and transient left
ventricular weight loss. Maximal O2 consumption at 30 min
of hypoxia was reduced to 60% of the normoxic value and remained
unchanged. This was partly due to a gradual decrease in maximal cardiac
output and heart rate (HRmax), which offset the increase in
blood O2 content. HRmax correlated
positively (r = 0.994) with -adrenoceptor density
and negatively (r = 
0.964) with M-Ach-receptor
density, suggesting that HRmax reduction results from
intrinsic changes in myocardial receptor characteristics leading to
reduced responses to adrenergic stimulation and elevated responses to
cholinergic stimulation. -Adrenoceptor density in both ventricles
increased initially to eventually fall below normoxic values. The
dissociation between the different patterns of right and left
ventricular weight and the similar pattern of -adrenoceptor change
in both ventricles do not support a role for these receptors on right
ventricular myocardial hypertrophy.
muscarinic receptor; -adrenoceptor; -adrenoceptor; maximal
exercise heart rate; maximal exercise cardiac output; maximal
O2 consumption
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