Changes in inspiratory activity after injection of adenosine and hypoxanthine in cats

The effects of intra-arterial and intravenous injections of adenosine and hypoxanthine were investigated with special reference to respiratory variables in anesthetized young cats. Studies were made of the effects on inspiratory activity (phrenic nerve activity), heart rate, blood pressure and central venous pressure. To assess the risk of accumulation of adenosine degeneration products after several injections measurements were also made of hypoxanthine, xanthine and urate in plasma at intervals after the injections. It was found that intra-arterial and intravenous injections of adenosine increased central inspiratory activity during the first few breaths after the injection. The blood pressure and heart rate decreased slightly and central venous pressure increased slightly after the injection. Degradation of adenosine and its metabolites takes place rapidly and it is therefore unlikely that metabolites influence the results. It is concluded that adenosine causes brief stimulation of inspiratory activity.