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Experimental Anesthesia, Clinics of Anesthesiology and Operative Intensive Care Medicine, Charité, D-13353 Berlin, Germany
This study investigated whether adenosine
mediates the decrease in plasma renin activity (PRA) during acute
hypoxia. Eight chronically tracheotomized, conscious beagle
dogs were kept under standardized environmental conditions and received
a low-sodium diet (0.5 mmol · kg body
wt
1 · day
1). During the experiments,
the dogs were breathing spontaneously via a ventilator circuit: first
hour, normoxia (21% inspiratory concentration of O2);
second and third hours, hypoxia (10% inspiratory concentration of
O2). Each of the eight dogs was studied twice in randomized
order in control and theophylline experiments. In theophylline
experiments, theophylline, an A1-receptor antagonist, was
infused intravenously during hypoxia (loading dose: 3 mg/kg within 30 min, maintenance: 0.5 mg · kg
1 · h
1). In
theophylline experiments, PRA (5.9 ± 0.8 ng ANG
I · ml
1 · h
1) and ANG II
plasma concentration (15.9 ± 2.3 pg/ml) did not decrease during
hypoxia, whereas plasma aldosterone concentration decreased from
277 ± 63 to 132 ± 23 pg/ml (P < 0.05). In
control experiments, PRA decreased from 6.8 ± 0.8 during normoxia
to 3.0 ± 0.5 ng ANG I · ml
1 · h
1 during
hypoxia, ANG II decreased from 13.3 ± 1.9 to 7.3 ± 1.9 pg/ml, and plasma aldosterone concentration decreased from 316 ± 50 to 70 ± 13 pg/ml (P < 0.05). Thus infusion of
the adenosine receptor antagonist theophylline inhibited the
suppression of the renin-angiotensin system during acute hypoxia. The
decrease in aldosterone occurred independently and is apparently
directly related to hypoxia. In conclusion, it is likely that adenosine mediates the decrease in PRA during acute hypoxia in conscious dogs.
angiotensin II; aldosterone; theophylline
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