Effects of high-altitude chronic hypoxia on platelet alpha 2-receptors in man.
During chronic high-altitude (HA) exposure, basal and exercise-induced noradrenaline (NA) increases do not parallel blood pressure (BP) changes observed; unlike beta-adrenergic receptors, to our knowledge no data are available on alpha-receptors. We studied platelet alpha 2- and leucocyte beta-receptors and basal catecholamine levels in 11 trained climbers before and after they had spent a 15-day period at a height of over 4400 m. In six of the climbers we also evaluated catecholamines after maximal bicycle ergometer exercise. After chronic high-altitude exposure, a significant decrease was found in platelet alpha 2-receptor density and affinity [Bmax from 92.6 +/- 6.7 to 54.6 +/- 4.2 fmol mg-1 protein (P < 0.001) and KD from 1.271 +/- 0.034 to 1.724 +/- 0.077 nmol L-1 (P < 0.05)], although no changes to beta-receptors were observed. No changes were found in basal pre- and post-expedition NA and adrenaline (A), and there was only a slight decrease in post-expedition NA after maximal exercise. Our results suggest that prolonged exposure to hypoxia induces a down-regulation of alpha 2-receptors, which may be a contributory factor in the regulation of the physiological vascular response to acclimatization.
Zaccaria
M
M
Division of Internal Medicine (Sports Medicine Unit), University of Padua, Italy.
Borea
P A
PA
Opocher
G
G
Ponchia
A
A
Varani
K
K
Fraccarollo
D
D
Scandellari
C
C
D000328:Adult; D000531:Altitude; D002908:Chronic Disease; D015444:Exercise; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000097:blood*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D018341:Receptors, Adrenergic, alpha-2 / Q000097:blood*
D018341:Receptors, Adrenergic, alpha-2; D009638:Norepinephrine