MICRODIALYZED ADENOSINE IN NUCLEUS-TRACTUS-SOLITARII AND VENTILATORY RESPONSE TO HYPOXIA IN PIGLETS

Levels of adenosine, inosine, and hypoxanthine from the interstitial s pace at the nucleus tractus solitarii were measured by microdialysis i n eight 20- to 25-day-old anesthetized spontaneously breathing piglets . Microdialyzed samples were collected every 30 min for 2 h after the insertion of the probe to ensure stability of purine levels and then d uring 30 min each of normoxia, hypoxia (10% O-2-90% N-2), and normoxia . The purines were separated by high-pressure liquid chromatography wi th ultraviolet detection and quantified at 254-nm wavelength. Tidal vo lume, breathing frequency, minute ventilation, mean arterial blood pre ssure, pH, and gas tensions were measured. Compared with control, aden osine levels during hypoxia increased by 40.7 +/- 5.5% and then tended to decline during the recovery from hypoxia, but the levels remained higher than in control. Ventilatory measures exhibited a modest biphas ic pattern during hypoxia and resumed control values by 10 min after t he removal of the hypoxia. The increased adenosine release during hypo xia provides additional evidence for the possible participation of ade nosine in the central suppression of breathing during hypoxia.