Effect of adenosine on carotid chemoreceptor activity in the cat.

1 The effects of intracarotid (i.c.) injections or infusions of adenosine on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve have been studied in cats anaesthetized with pentobarbitone. 2 Adenosine injections (0.1-100 micrograms) caused a rapid and marked increase of spontaneous chemoreceptor discharge, the intensity, duration and onset of which was dose-dependent. Infusion of adenosine, 50 microgram/min, also evoked an increase in discharge which persisted for the duration of the infusion. 3 Both theophylline (1 mg i.c.) and aminophylline (1 mg i.c.) caused short-lasting decreases in spontaneous discharge but did not prevent the excitatory effect of adenosine. Theophylline increased the excitatory action of adenosine. 4 Naloxone (400 micrograms i.c.) antagonized the depressant effect of morphine on chemoreceptor discharge but not the excitatory action of adenosine. 5 It is concluded that exogenous adenosine can excite the cat carotid chemoreceptors, an effect which is not prevented by theophylline in the doses studied. The physiological significance of the findings is discussed.