A useful muscarinic parameter and the differential recording of atrial and ventricular tension in the perfused rabbit heart.

Abstract

1. A simple method of recording right atrial tension from the Langendorff perfused rabbit has been described; it is based on the “transverse” method of recording cardiac contractions described by Beckett (1970). 2. Right atrial and ventricular tensions were recorded by transducers attached to threads stitched into the right atrium and right ventricle, the heart being retained and prevented from rotating by two threads stitched into the intraventricular septum as described by Beckett. 3. Right ventricular diastolic tension was adjusted to 7.5 g. Interference with the atrial record by ventricular systole was overcome by adjustment of diastolic right atrial tension to its optimal value between 1 and 1.5 g. 4. Sympathetic nerve stimulation and infusions of sympathomimetic drugs increased atrial and ventricular tension development and ventricular rate but no differential effects were observed. Conversely, vagal nerve stimulation and particularly infusions of muscarinic drugs markedly depressed atrial tension development at a time when ventricular tension and rate were little affected. 5. Besides providing an additional pharmacological parameter, the main advantage of recording atrial tension is in the quantitative evaluation of muscarinic activity in the whole perfused heart. Further, measurement of right atrial tension affords a useful method of detecting muscarinic activity in those drugs (e.g. ganglion stimulants) which have mixed parasympathetic and sympathetic cardiac actions.