Characterization of adenosine receptors in isolated cerebral arteries of cat

Abstract

1 The effect of some adenosine analogues and xanthine derivatives were studied on isolated cerebral arteries from cats. 2 The adenosine analogues caused an almost complete relaxation of cerebral arteries contracted by prostaglandin F_2α (PGF_2α, 30 μm). The order of potency was: 5-N-ethylcarboxamide adenosine (NECA) > 2-chloroadenosine > adenosine > l-N⁶-phenylisopropyl adenosine (l-PIA). The analogue d-PIA was very weak and its maximum effect was small. 3 NECA and l-PIA enhanced [³H]-cyclic AMP accumulation in [³H]-adenine labelled feline pial vessels with similar absolute and relative potency to their relaxant effects. 4 The relaxant effects of adenosine and of NECA were competitively antagonized by 8-phenyl-theophylline (pA₂ = 6.5). The effect of theophylline and enprofylline could not be tested in higher concentrations than 30 or 10 μm because they affected the vessels directly. At these concentrations they were essentially inactive as adenosine antagonists. The non-xanthine phosphodiesterase inhibitor rolipram (0.1 and 100 μm) caused a slight but non-significant potentiation of the relaxant effect of adenosine. 5 The results are compatible with the opinion that adenosine relaxes cerebral vessels by an action on adenosine A₂-receptors. The effect may be linked to adenylate cyclase and can be antagonized by 8-phenyl-theophylline.