Journal of Applied Physiology, Vol 77, Issue 4 1763-1768, Copyright © 1994 by American Physiological Society
Effect of aminophylline on plasma [K+] and hypoxic ventilatory response during mild exercise in men
T. Igarashi, M. Nishimura, Y. Akiyama, M. Yamamoto, K. Miyamoto and Y. Kawakami
First Department of Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
To examine the role of endogenous adenosine on the hypoxic ventilatory
response (HVR) enhanced during exercise, we measured HVR at rest and during
mild exercise (12.5 W) in nine healthy men in a supine position after
pretreatment with aminophylline (5 mg/kg), an adenosine receptor blocker,
or dipyridamole (0.6 mg/kg), an adenosine uptake blocker, by using a 3-day
double-blind placebo-controlled design. Although HVR was enhanced during
exercise on all occasions, HVR with aminophylline [0.42 +/- 0.07 (SE)
l.min-1.%fall-1 of arterial O2 saturation] was significantly lower than
that with placebo (0.64 +/- 0.13 l.min-1.%fall-1) or dipyridamole (0.64 +/-
0.08 l.min-1.%fall-1) during exercise (P < 0.05 for both) at similar
end-tidal PCO2 on the 3 days but not at rest. We then examined the changes
in plasma K+ concentration ([K+]) and catecholamines, the other possible
endogenous potentiators of the carotid body activity. The exercise- and
hypoxia-induced increases in plasma [K+] were significantly lower with
aminophylline (0.23 +/- 0.09 meq/l) than with the placebo (0.51 +/- 0.10
meq/l) or dypyridamole (0.58 +/- 0.13 meq/l) (P < 0.05 for both). We
therefore conclude that aminophylline attenuates the enhancement of HVR
during mild exercise and that this might be due to its attenuating effect
on exercise- and hypoxia-associated increases in plasma [K+] rather than
due to its antagonizing effect on endogenous adenosine.
