Differences between receptors for 5-hydroxytryptamine on autonomic neurones revealed by nor-(-)-cocaine.
1 The interaction between nor-(-)-cocaine and 5-hydroxytryptamine (5-HT) at autonomic neuronal 5-hydroxytryptamine (5-HT) receptors has been investigated on the rabbit heart and guinea-pig ileum. 2 The chronotropic response to 5-HT mediated through activation of receptors on the terminal sympathetic fibres of the rabbit heart was antagonized selectively and surmountably by nor-(-)-cocaine. Schild analysis yielded a pA2 value for the interaction of 7.79 +/- 0.11, n = 13. 3 On the guinea-pig ileum induced to contract by activation of 5-HT receptors on the intramural cholinergic nerves, nor-(-)-cocaine was also a selective and surmountable antagonist of 5-HT, although the concentrations needed were higher than those shown to be effective on the heart. The pA2 value for the interaction was 6.49 +/- 0.07, n = 16. 4 The differential blocking effect of nor-(-)-cocaine in the two tissues suggests that the receptors for 5-HT on the cholinergic nerves of the ileum and the sympathetic fibres of the heart are different. The data thus lend support to the earlier similar conclusion based on the observation that 5-methoxytryptamine is a potent agonist on the ileum yet inactive on the heart.
D000818:Animals; D003042:Cocaine / Q000031:analogs & derivatives*; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D011817:Rabbits; D011985:Receptors, Serotonin / Q000187:drug effects*; D012702:Serotonin Antagonists
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; C008671:norcocaine; D003042:Cocaine