ADENOSINE-ANALOGS INHIBIT ACETYLCHOLINE-RELEASE AND CYCLIC-AMP SYNTHESIS IN THE GUINEA-PIG SUPERIOR CERVICAL-GANGLION

The ability of adenosine agonists to modulate the electrically evoked release of acetylcholine (ACh) from [H-3]choline preloaded guinea-pig superior cervical ganglia (SCG) was investigated. The adenosine Al-rec eptor selective agonist N-6-cyclohexyladenosine (CHA) and 2-chloroaden osine (2-CADO) inhibited the evoked transmitter release, the effect be ing reversed by the Al-receptor selective antagonist 8-cyclopentyl-1,3 -dipropylxanthine (DPCPX), and by sulmazole (SUL), which blocks both t he Al-receptor and the adenylate cyclase inhibitory regulator Gi. In w hole ganglia, CHA decreased both the basal and the forskolin (FSK)-sti mulated cyclic AMP synthesis. The latter effect was again prevented by the Al antagonist DPCPX. These results are compatible with the existe nce, in the guinea-pig SCG, of adenosine Al-receptors, part of which a re located on the presynaptic nerve terminals mediating an inhibition of ACh release.