Pharmacological characterization of the receptor involved in chemoexcitation induced by adenosine

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Abstract
1 Experiments were performed on cats anaesthetized with pentobarbitone in which carotid body chemoreceptor activity was recorded from the peripheral end of a sectioned carotid nerve. 2 Intracarotid (i.c.) injections of adenosine and its analogues, NECA (5′-N-ethylcarboxamidoadenosine), L-PIA (L-N6-phenylisopropyladenosine), and D-PIA (D-N6-phenylisopropyladenosine), caused dose-related increases in chemosensory discharge. The rank order of potency as chemoreceptor stimulants was: NECA > adenosine > L-PIA > D-PIA. 3 Infusion of theophylline antagonized the chemoexcitatory effects of NECA, and infusion of 8-phenyltheophylline (8-PT), which is a more potent adenosine antagonist with less activity as a phosphodiesterase inhibitor, reduced the chemoexcitation induced by adenosine. 4 Infusion of 8-PT (10 μg min−1 i.c.), a dose which substantially reduced the effect of injected adenosine, also reduced the sensitivity of carotid chemoreceptors to hypoxia (10% O2 for 4 min). 5 It is concluded that the adenosine receptors in the cat carotid body which mediate chemosensory excitation are xanthine-sensitive and appear to be of the A2 sub-type. Adenosine, released within the carotid body by physiological stimuli, may be involved in chemoexcitation.