BETA-ADRENERGIC-BLOCKADE DOES NOT PREVENT POLYCYTHEMIA OR DECREASE INPLASMA-VOLUME IN MEN AT 4300 M ALTITUDE

When humans ascend to high altitude (ALT) their plasma volume (PV) and total blood volume (BV) decrease during the first few days. With cont inued residence over several weeks, the hypoxia-induced stimulation of erythropoietin increases red cell production which tends to restore B V. Because hypoxia also activates the beta-adrenergic system, which st imulates red blood cell production, we investigated the effect of adre nergic beta-receptor inhibition with propranolol on fluid volumes and the polycythemic response in 11 healthy unacclimatized men (21-33 year s old exposed to an ALT of 4300 m (barometric pressure 460 Torr) for 3 weeks on Pikes Peak, Colorado. PV was determined by the Evans blue dy e method (PVEB), BV by the carbon monoxide method (BVCO), red cell vol ume (RCV) was calculated from hematocrit (Hct) and BVCO, and serum ery thropoietin concentration ([EPO]) and reticulocyte count, were also de termined. All determinations were made at sea level and after 9-11 (AL T-10) and 19-20 (ALT-20) days at ALT. At sea level and ALT, six men re ceived propranolol (pro, 240 mg.day(-1)), and five received a placebo (pla). Effective beta-blockade did not modify the mean (SE) maximal va lues of [EPO] [pla: 24.9 (3.5) vs pro: 24.5 (1.5) mU.ml(-1)] or reticu locyte count [pla: 2.7 (0.7) vs pro: 2.2 (0.5)%]; nor changes in PVEB [pla: -15.8 (3.8) vs pro: -19.9 (2.8)%], RCVCO [pla: +7.0 (6.7) vs pro : +10.1 (6.1)%], or BVCO [pla: -7.3 (2.3) vs pro: -7.1 (3.9)%]. In the absence of weight loss, a redistribution of body water with no net lo ss is implied. Hence, activation of the beta-adrenergic system did not appear to affect the hypovolemic or polycythemic responses that occur red during 3 weeks at 4300 m ALT in these subjects.