Evidence that the renin decrease during hypoxia is adenosine mediated in conscious dogs

This study investigated whether adenosine mediates the decrease in plasma r enin activity (PRA) during acute hypoxia. Eight chronically tracheotomized, conscious beagle dogs were kept under standardized environmental condition s 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 cir cuit: first hour, normoxia (21% inspiratory concentration of O-2); second a nd third hours, hypoxia (10% inspiratory concentration of O-2). Each of the eight dogs was studied twice in randomized order in control and theophylli ne experiments. In theophylline experiments, theophylline, an A(1)-receptor antagonist, was infused intravenously during hypoxia (loading dose: 3 mg/k g within 30 min, maintenance: 0.5 mg.kg(-1).h(-1)). In theophylline experim ents, PRA (5.9 +/- 0.8 ng ANG I.ml(-1).h(-1)) and ANG II plasma concentrati on (15.9 +/- 2.3 pg/ml) did not decrease during hypoxia, whereas plasma ald osterone concentration decreased from 277 +/- 63 to 132 +/- 23 pg/ml (P < 0 .05). In control experiments, PRA decreased from 6.8 +/- 0.8 during normoxi a to 3.0 +/- 0.5 ng ANG I.ml(-1).h(-1) during hypoxia, ANG II decreased fro m 13.3 +/- 1.9 to 7.3 +/- 1.9 pg/ml, and plasma aldosterone concentration d ecreased from 316 +/- 50 to 70 +/- 13 pg/ml (P, 0.05). Thus infusion of the adenosine receptor antagonist theophylline inhibited the suppression of th e renin-angiotensin system during acute hypoxia. The decrease in aldosteron e 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.