Respiration Physiology 107 (1997) 75 – 84
Role of -adrenergic and cholinergic systems in acclimatization
to hypoxia in the rat
Richard L. Clancy
a
, Yoshihiro Moue
b
, Lars P. Erwig
c
, Peter G. Smith
a
,
Norberto C. Gonzalez
a,
*
a
Department of Physiology, Uniersity of Kansas Medical Center, 3901 Rainbow Bouleard, Kansas City, KS 66 160 -7401, USA
b
Department of Medicine, Tokai Uniersity Medical School, Isehara, Kanagawa 259 -11, Japan
c
Abteilung Arbeit -und -Sportphysiologie, Medizinische Hochschule, Hannoer 30 625, Germany
Accepted 21 October 1996
Abstract
The role of -adrenergic and muscarinic cholinergic systems on maximal treadmill exercise performance and
systemic O
2
transport during hypoxic exercise (PI
O
2
70 Torr) was studied in rats acclimatized to hypobaric hypoxia
(PI
O
2
70 Torr for 3 weeks, A rats) and in non-acclimatized littermates (NA rats). Untreated A rats had lower resting
(fH) and maximal heart rate (fHmax) and cardiac output (Q ), and higher maximal O
2
uptake (V
O
2
max
) than NA. The
only effect of cholinergic receptor blockade with atropine (Atp) was an increase in pre-exercise fH to comparable
levels in A and in NA.
1
-adrenergic receptor blockade with atenolol (Aten) lowered pre-exercise fH and (fHmax) to
comparable values in A and in NA rats. However, since both pre-exercise fH and fHmax were lower in untreated A,
the effect of Aten was relatively smaller in A. Aten reduced maximal exercise cardiac output (Q
max
) in NA; however,
tissue O
2
extraction increased such that V
O
2
max
was not affected. Aten did not influence Q
max
or any other parameter
of systemic O
2
transport in A. In conclusion the increased cholinergic tone may be responsible for the lower resting
fH but not the lower fHmax of A; the integrity of the -adrenergic system is not necessary to attain V
O
2
max
in hypoxia
either in A or in NA; the decreased response to -adrenergic stimulation in A limits the efficacy of this system on
the mechanisms of systemic O
2
transport and reduces the effect of its blockade on these mechanisms. © 1997 Elsevier
Science B.V.
Keywords: Acclimatization, hypoxia; Exercise, maximal, hypoxia, adrenergic, cholinergic systems; Hypoxia, acclima-
tized; Mammals, rats
* Corresponding author. Tel.: +1 913 5887025; fax: +1 913 5887430; e-mail: ngonzale@kumc.edu
0034-5687/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved.
PII S0034-5687(96)02502-9