EFFECTS OF DESENSITIZATION TO ADENOSINE 5′‐TRIPHOSPHATE AND ADENOSINE ON NON‐ADRENERGIC INHIBITORY RESPONSES IN THE CIRCULAR MUSCLE OF RABBIT COLON

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Abstract
An approximate eight fold desensitization of the circular coat of the distal rabbit colon to adenosine 5′‐triphosphate (ATP) and adenosine could be achieved by repeatedly exposing the organ to relatively low concentrations (10–100 μm) of these compounds. The desensitization was specific and reversible after prolonged washing. It could be overcome by increasing the concentrations of the purine agonists. Dipyridamole potentiated the non‐adrenergic inhibition in response to transmural stimulation but failed to influence the caudad relaxation evoked by radial distension. Desensitization to ATP and adenosine (and to ATP + adenosine simultaneously) did not affect the non‐adrenergic inhibition in response to radial distension or transmural stimulation. These results suggest that neither ATP nor adenosine are the final transmitters mediating the non‐adrenergic inhibitory responses in the distal colon of the rabbit.

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