Procaine-induced positive chronotropic and inotropic responses of the isolated, blood-perfused dog atrium.

In the isolated, blood-perfused canine atrium preparations, procaine given into the cannulated sinus node artery induced frequently significantly positive chronotropic and inotropic effects at a dose level of 30-1000 microng. Above a dose of 100 microng, initially brief negative chronotropic and inotropic effects were usually observed. Procaine-induced negative effects were not blocked by an adequate dose level of atropine. Procaine-induced positive effects were inhibited by treatment with propranolol but not modified by tetrodotoxin or desmethylimipramine. Procaine suppressed acetylcholine-induced negative chronotropic and inotropic effects. On the other hand, procaine did not block norepinephrine-induced positive inotropic and chronotropic effects. From these results, it is concluded that procaine may have sympathomimetic and atropine-like properties.