title: Adrenergic status of humans during prolonged exposure to the altitude of 6,542 m.
abstract: Plasma norepinephrine (NE) concentration increases with altitude exposure while maximal heart rate (HR) and chronotropic response to isoproterenol (IP) are blunted. Downregulation of cardiac beta-adrenergic receptors (beta-AR) has been evoked to explain this phenomenon. Chronotropic response was studied at extreme altitude in 10 subjects (4 women, 6 men; aged 35 +/- 6 yr). Observations were made in normoxia (N) and after 1 (H1) and 3 (H3) wk at 6,542 m. Acclimatization was accomplished by gradual climbing from 4,000 to 6,542 m over 10 days. Plasma NE was obtained at rest and during submaximal exercise. Successive doses of IP (0.02, 0.04, and 0.06 microgram/kg-1.min-1) were infused for 5 min each. Density and affinity of lymphocyte beta 2-AR were also measured. Increase in HR for maximal dose of IP decreased from 57 +/- 12 to 34 +/- 7 and 37 +/- 10 min-1 in H1 and H3, respectively (P < 0.001 for both). IP dose for which HR rises by 25 min-1 (I25) increased from 27 +/- 5 in N to 42 +/- 10 and 43 +/- 17 ng.kg-1.min-1 in H1 and H3, respectively (P < 0.001 for both). Arterial O2 saturation at rest was 98 +/- 2% in N, 72 +/- 6% in H1 (P < 0.001), and 79 +/- 5% in H3 (P < 0.001). The chronotropic response was neither restored nor further attenuated after 3 wk at 6,542 m. Plasma NE levels at rest and during exercise were higher at 6,542 m than values obtained in previous studies at 4,350 and 4,800 m.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Association pour la Recherche en Physiologie de l'Environnement, Bobigny, France.
authors.forename: A M
authors.initials: AM
authors.lastname: Antezana
authors.forename: R
authors.initials: R
authors.lastname: Kacimi
authors.forename: J L
authors.initials: JL
authors.lastname: Le Trong
authors.forename: M
authors.initials: M
authors.lastname: Marchal
authors.forename: I
authors.initials: I
authors.lastname: Abousahl
authors.forename: C
authors.initials: C
authors.lastname: Dubray
authors.forename: J P
authors.initials: JP
authors.lastname: Richalet
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000328:Adult; D000332:Aerobiosis / Q000502:physiology; D000531:Altitude; D001794:Blood Pressure / Q000502:physiology; D004452:Echocardiography; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology; D008214:Lymphocytes / Q000502:physiology; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010100:Oxygen / Q000097:blood; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol; D010100:Oxygen; D009638:Norepinephrine