ON THE INABILITY TO PRODUCE SUPERSENSITIVITY TO CATECHOLAMINES IN INTESTINAL SMOOTH MUSCLE

¹ Department of Pharmacology, The University of Texas Southwestern Medical School, Dallas, Texas

Several responses to catecholamines are not potentiated by cocaine. One of these responses, the relaxation of intestinal smooth muscle, has been examined in detail with a preparation of the longitudinal muscle and Auerbach's plexus from guinea-pig ileum. No supersensitivity to cocaine or desipramine could be unmasked by alpha or beta receptor blockade or by catechol-O-methyltransferase or monoamine oxidase inhibition. However, the amine content, K_m of amine uptake and ED50 of drugs inhibiting amine uptake in the nerves of Auerbach's plexus have been evaluated and found to be comparable to systems in which supersensitivity does occur. It is proposed that the variable which accounts for the lack of supersensitivity in the intestinal system is the size of the synaptic cleft.