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

Abstract

1 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. 2 The desensitization was specific and reversible after prolonged washing. It could be overcome by increasing the concentrations of the purine agonists. 3 Dipyridamole potentiated the non-adrenergic inhibition in response to transmural stimulation but failed to influence the caudad relaxation evoked by radial distension. 4 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. 5 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.