A simple technique for determining contractility, intraventricular pressure, and heart rate in the anesthetized guinea pig.

This paper describes a rapid technique for the continuous recording of intraventricular pressure, dP/dt, and heart rate in the anesthetized guinea pig. A 21g needle, attached to a pressure transducer, is inserted through the chest wall into the left ventricle. This provides continuous monitoring of intraventricular pressure; the first derivative of this pressure pulse is dP/dt, an index of inotropic state. The ventricular signal is also used to trigger a cardiotach for the continuous recording of heart rate. Since major surgery is not required, experimental set-up can be completed in 15-20 min with a minimum of trauma to the animal. This model is ideally suited for the determination of cardiovascular parameters following the administration of drugs by several routes (intravenous, oral, intramuscular, subcutaneous). The effects of three distinct inotropic agents: isoproterenol, AR-L57, and ouabain, have been evaluated in this system. Isoproterenol increased heart rate and dP/dt, and caused a transient increase in peak intraventicular pressure. AR-L57 and ouabain increased dP/dt and intraventricular pressure; their effects on heart rate were minimal. Ouabain was active following either oral or intravenous administration.