Acclimatization to 4,300 m altitude decreases reliance on fat as a
substrate.
Roberts, A. C., G. E. Butterfield, A. Cymerman, J. T. Reeves, E. E.
Wolfel, and G. A. Brooks.
UNIVERSITY OF CALIFORNIA AT BERKELEY, BERKELEY, CALIFORNIA 94720;
UNIVERSITY OF COLORADO HEALTH SCIENCES CENTER, DENVER, CO, 80262; US
ARIEM, NATICK, MA 01760; AND GRECC, PALO ALTO VA MEDICAL CENTER, PALO
ALTO, CA, 95304
APStracts 3:0121A, 1996.
We tested the hypothesis that exposure to altitude decreases reliance
on free fatty acids (FFA) as substrates and increases dependency on
blood glucose. Therefore, the effects of exercise, hypobaric hypoxia,
and altitude acclimatization on FFA, glycerol and glucose net uptake
and release [= 2 (leg blood flow) (arterial-venous concentration)],
and fatty acid (FA) consumption (=3 x glycerol release + FFA uptake)
by the legs were measured. Because sympathetic responses have been
implicated, we utilized non-specific [beta]-blockade (oral
propranolol 80 mg 3 x/day) and observed responses to exercise,
altitude and altitude acclimatization. We studied six healthy [beta]
-blocked men ([beta]) and five matched controls (C) during rest and
cycle ergometry exercise (88 W) at 49% of sea level (SL) V02peak at
the same absolute power output on acute altitude exposure (A1; Pb =
430 mm Hg), and after 3 weeks of chronic altitude exposure to 4,300 m
(A2). At sea level, resting FA consumption rates were 0.08+0.02 (C)
and 0.05+0.04 ([beta]) mmol/min, respectively. During exercise at SL,
FA consumption rates increased to 0.90+0.32 (C) and 0.94+0.19
([beta]) mmol/min (P< 0.05), respectively. Upon arrival at 4,300
m resting leg FFA uptake and FA consumption rates were not
significantly different from those at SL. However, after
acclimatization to altitude, at rest leg FA consumption decreased to
essentially zero in both (C) and ([beta]) groups. During exercise at
altitude after acclimatization leg FA consumption increased
significantly from rest to C=0.25+0.10 and [beta]=0.10+ 0.20
mmol/min, but values were less than at SL or A1 (P< 0.05), while
glucose uptake increased relative to SL values. Furthermore, [beta]
-blockade significantly increased glucose uptake relative to control.
We conclude that: 1) chronic altitude exposure decreases leg FA
consumption during rest and exercise, 2) relative to SL, FFA uptake
decreases while glucose uptake increases during exercise at altitude,
and 3) [beta]-blockade potentiates these effects.
Received 12 September 1994; accepted in final form 15 February
1996.
APS Manuscript Number A959-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96