The effect of adenosine on respiratory chemosensitivity in the awake rat.

The effect of adenosine on respiration and respiratory chemosensitivity in awake animals was studied in rats, intact and chemodenervated, before and after intra-peritoneal injection of L-phenylisopropyladenosine (PIA). Respiration was measured by barometric plethysmography. The administration of PIA depressed respiration substantially, in a dose-related manner, the maximum effect occurring after 30-80 min; PIA also depressed body temperature but over a slower time course. In both intact and chemodenervated animals, the characteristic responses to hypoxia were maintained after the administration of PIA, but at depressed respiratory levels. There was no interaction between effects. Administration of PIA produced enhancement of the ventilatory response to hypercapnia, in both intact and peripherally chemodenervated animals. The results do not support the hypothesis that hypoxic effects on respiration are related to the accumulation of adenosine in brain tissues. Enhancement of the hypercapnic response represents evidence for disinhibition of the mechanism concerned.