Abstract
The effects of adenosine and its related compounds on the cholinergic twitch response were examined in electrically stimulated guinea pig ileum. Adenosine (3×10-7-10-5 M) and an adenosine A1-receptor agonist N6-cyclohexyladenosine (CHA, 10-8-10-6 M) suppressed the twitch. Conversely, the A2a-receptor agonist 2-[p-(2-carboxyethyl)phenethylamino]-5’-N-ethylcarboxamidoadenosine (CGS 21680, 10-9-10-7M) potentiated the twitch in half the preparations examined. The A1-antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), which per se did not affect the twitch, recovered the attenuated twitch caused by CHA (10-7 M) or adenosine (10-6 M) and converted it into a potentiated twitch. These results suggest the presence of adenosine A1- and A2a-receptors coupled negatively and positively, respectively, to acetylcholine release in the preparation.
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