Action of local anesthetics on basal tone of rat vas deferens and on response to norepinephrine and calcium.

The actions of three local anesthetics (cocaine, procaine and tetracaine) on basal tone of isolated vas deferens from control and reserpinized rats were studied. The influence of these anesthetics on responses to norepinephrine and calcium was also examined. Cocaine, procaine and tetracaine, in the order, induced phasic and tonic contractions, the latter ones probably due to catecholamine release. The local anesthetics, at the lowest doses, produced an elevation of the maximum response to norepinephrine, as well as a leftward shift of the dose-response curve. The highest doses of local anesthetics inhibited the response to norepinephrine in a non-competitive way, while the response to calcium was competitively inhibited. In this connection, tetracaine proved to be the most active compound. The distinction between destabilizing and stabilizing effects on membrane is pointed out and discussed.