Atsushi Tomaru (#), Yasuhiro Ina, Nobuyuki Kishibayashi and Akira Karasawa
Department of Pharmacology, Pharmaceutical Research Laboratories, Kyowa Hakko Kogyo Co., Ltd., 1188 Shimotogari, Nagaizumi-cho, Sunto-gun, Shizuoka 411, Japan
(#) Present address: Pharmaceuticals Research and Development Center, Kyowa Hakko Kogyo Co., Ltd., 1-6-1 Ohtemachi, Chiyoda-ku, Tokyo 100, Japan
Abstract: The effects of adenosine and its related compounds on the cholinergic twitch response were examined in electrically stimulated guinea pig ileum. Adenosine (3 x 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, 10-9-10-7 M) 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 A2-receptors coupled negatively and positively, respectively, to acetylcholine release in the preparation.
Keywords: Adenosine receptor, Twitch response, Ileum