ABSTRACT
Heart rate (FC) response to perfusion with isoprenaline is decreased in sealevel natives on expuser to high altitude hypoxia. Since noredraline concentration in plasma is elevated under these condition as phenomenon of downregulation of the betareceptors (BAR) cuold be evoked. For the fisrt time, this aspect was explored in a population native from and residing at 3600 m consisting of normocythemics (HAN) and polycythemics (HAP). the results were compared to those obtained from a sealevel population, exmined in normoxia (SLN) at 4800 m (J. Appl. Physiol. 65:1975-61, 1988). The dose necessary to increase FC by 25 beats per min (125) was identical for HAN and HAP as well as SLN. This iondicates that the chronotropic responses is igual in the two populations when they are studied in their habitual environment; to the contrary, this response is diminished in SLH, thus correlating to the phenomenon of downregulation.