Increased arterial pressure after acclimatization to 4300 m: possible role of norepinephrine.

Both systemic arterial pressure and sympathetic activity increase at high altitude, but neither the time course of these increases nor the relationship between them are known. Examination of resting and exercising data from our prior studies at sea level and on Pikes Peak indicated that blood epinephrine concentrations either showed little change (from sea level) or rose early in altitude exposure and then declined with acclimatization. By contrast, norepinephrine concentrations in blood and urine were not increased on arrival but consistently rose later in the acclimatization process. Also with altitude exposure, arterial pressure also increased concomitantly with the increase in norepinephrine concentrations. The study designs were not adequate to establish cause and effect, but the results were consistent with the concept that arterial pressure increments at altitude were associated with increased alpha adrenergic-mediated vascular tone.