ACTIONS AND INTERACTIONS OF ETHANOL AND IMIPRAMINE ON THE RAT SINUS NODE

We studied the actions and interactions of ethanol and imipramine on t he sinus node. Strips of the right rat atrium including the sinus node were superfused with Tyrode's solution at 37 degrees C while beating spontaneously. The preparations were exposed to imipramine or ethanol alone as well as to the two drugs in combination while recording membr ane potentials with standard intracellular microelectrodes. The result s obtained show that ethanol 0.8 and 2.4 g/l exerted a positive chrono tropic action. On the other hand, imipramine 0.25 mg/l did not modify the sinus node rate. However, it reduced significantly the positive ch ronotropic action of ethanol. The sinus node rate decreased under the action of a higher concentration of imipramine (1 mg/l). When ethanol was tested in combination with this concentration of imipramine, the e ffect of the latter prevailed. In conclusion, a concentration of imipr amine that did not affect the sinus node rate antagonized the positive chronotropic action of ethanol. In addition, the negative chronotropi c action of a higher concentration of imipramine prevailed over the po sitive action of ethanol. The results obtained provide additional supp ort to the notion that the use of ethanol and cardioactive drugs in co mbination may result in significant changes in the actions of either o f the two, or both. This is of clinical relevance, since at least some of the individuals under treatment with cardioactive drugs will be al coholics and/or social drinkers. (C) 1997 Elsevier Science Ireland Ltd .