title: Influence of adenosine, cAMP and db-cAMP on responses of the isolated terminal guinea-pig ileum to electrical stimulation.
abstract: Adenosine, cAMP and db-cAMP were found to inhibit nerve-mediated contractions of the terminal ileum elicited by electrical stimulation (ES). Responses to ES at 30 Hz, which are believed to be of adrenergic origin, were considerably more affected than the responses to ES at 3 Hz, which may be of purinergic orign. The following order of relative inhibitory potencies was established: adenosine greater than cAMP greater than db-cAMP. Adenosine, cAMP and db-cAMP did not affect the contractile responses of the preparation to histamine, potassium and noradrenaline. Therefore, the observed inhibition of nerve-mediated contractions was thought to be due to an action on presynaptic sites, i.e. on the neural network within the intestine. This action was antagonized by an increase in external calcium and by aminophylline, which is known to increase intracellular calcium. The present experiments suggests that the inhibitory action of adenosine, cAMP and db-cAMP results from a reduction of calcium fluxes across the neural membrane and to a subsequent reduction in the release of neurotransmitter(s). The inhibitory effect of cAMP appeared to be nonspecific and was presumably related to adenosine in its molecule.
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000628:Aminophylline / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004347:Drug Interactions; D004558:Electric Stimulation; D006168:Guinea Pigs; D007082:Ileum / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D013569:Synapses / Q000187:drug effects
chemical_list: D007093:Imidazoles; D000628:Aminophylline; D003994:Bucladesine; D000242:Cyclic AMP; D000241:Adenosine; D002118:Calcium