Enhanced synthesis of albumin and fibrinogen at high altitude

The acute effects of active and passive ascent to high altitude on plasma v olume (PV) and rates of synthesis of albumin and fibrinogen have been exami ned. Measurements were made in two groups of healthy volunteers, initially at low altitude (550 m) and again on the day after ascent to high altitude (4,559 m). One group ascended by helicopter lair group, n = 8), whereas the other group climbed (foot group, n = 9), so that the separate contribution of physical exertion to the response could be delineated. PV was measured by dilution of I-125-labeled albumin, whereas synthesis rates of albumin an d fibrinogen were determined from the incorporation of isotope into protein after injection of [ring-H-2(5)]phenylalanine. In the air group, there was no change in PV at high altitude, whereas, in the foot group, there was a 10% increase in PV (P < 0.01). Albumin synthesis(mg . kg(-1) . day(-1)) inc reased by 13% in the air group (P = 0.058) and by 32% in the foot group (P < 0.001). Fibrinogen synthesis (mg . kg(-1) .day(-1)) increased by 40% in t he air group (P = 0.068) and by 100% in the foot group (P < 0.001). Hypoxia and alkalosis at high altitude did not differ between the groups. Plasma i nterleukin-6 was increased modestly in both groups but C-reactive protein w as not changed in either group. It is concluded that increases in PV and pl asma protein synthesis at high altitude result mainly from the physical exe rcise associated with climbing. However, a small stimulation of albumin and fibrinogen synthesis may be attributable to hypobaric hypoxia alone.