Effects of local anaesthetics on short-term desensitization of guinea-pig taenia caecum to histamine.

1 Short-term desensitization to histamine was induced by incubating guinea-pig taenia caecum with 10−4 m histamine for 30 min (desensitizing incubation) in normal Locke-Ringer solution or Ca-free Locke-Ringer solution containing 0.2 mm EGTA. This desensitization was measured as a reduction of the maximal contractile response. 2 The effects of the presence of local anaesthetics during the desensitizing incubation were examined. Results showed that tetracaine, procaine, procainamide, oxybuprocaine and lignocaine inhibited the desensitization, whereas dibucaine, benzocaine and mepivacaine did not. 3 The inhibitory effects of these drugs on the desensitization were not correlated with their lipid solubility nor with the potency of their known effects, such as membrane stabilization, Ca channel blockade, calmodulin antagonism, or inhibition of C-kinase. 4 It is concluded that the inhibitory effects of local anaesthetics on the desensitization are not due to their non-specific membrane-stabilizing effects per se, but to some other action.