A possible explanation for a greater discrepant suppression by adenosine and N6-cyclohexyl adenosine of the guinea-pig ileal contraction.
Adenosine and N6-cyclohexyl adenosine (CHA) reduced dose-dependently a twitch contraction of guinea-pig ileum and their IC50 values were 1.0 X 10(-5) and 1.1 X 10(-8) M, respectively. By exposure to adenosine uptake and deaminase inhibitors, dipyridamole and erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), the adenosine-induced inhibition was enhanced, whereas the CHA-induced one was almost unchanged. Therefore, outstanding potency difference of the suppression by adenosine and CHA was minimized by concurrent addition of both the inhibitors. Uptakes of [3H]CHA into the guinea-pig ileum and taenia-coli were considerably lower than those of [3H]adenosine and were insensitive to dipyridamole. In the rat connective tissue segment, uptake of [3H]adenosine was smaller than that in the guinea-pig taenia-coli and ileal segments (especially, in the latter), and was virtually unaffected by 10(-5) M dipyridamole. These findings suggest that a greater discrepancy of the suppression by adenosine and CHA of the ileal twitch may substantially result from their different uptake and deamination in the synaptic region rather than their dissimilar intrinsic activity for the purinoceptor.
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D004176:Dipyridamole / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D011687:Purines / Q000378:metabolism; D013806:Theophylline / Q000494:pharmacology
D011687:Purines; C027513:N(6)-cyclohexyladenosine; D004176:Dipyridamole; D013806:Theophylline; D000241:Adenosine