EFFECT OF HYPERTONICITY ON CONTRACTILITY OF ISOLATED WORKING RAT LEFT-VENTRICLE

Objective: The aim was to evaluate the effect of hypertonic perfusate on isolated left ventricular mechanical and energetic characteristics. Methods: An isolated working rat heart model was perfused with a hyponatraemic Krebs-Heinseleit bicarbonate buffer (240 mOsmol.litre-1). To this buffer was added increasing amounts of mannitol to achieve 280, 320, and 360 mOsmol.litre-1 perfusates. Results: Left ventricular peak pressure, maximum time derivative of left ventricular pressure (dP/dt(max)), and end systolic pressure were all increased to a maximum value at 280 or 320 mOsmol.litre-1 perfusate tonicity. A similar response was evident with cardiac output, which changed from 33.7(SEM 0.6) to 43.5(0.8) ml.min-1 following changing the perfusate tonicity from 240 to 280 mOsmol.litre-1 (p less-than-or-equal-to 0.003). However, increasing perfusate tonicity further decreased cardiac output to 36.5(1.3) ml.min-1 at 360 mOsmol.litre-1. Maximal left ventricular elastance remained unchanged during perfusion with increasing perfusate tonicities. Conclusions: Changing perfusate osmolality using mannitol has a positive inotropic effect at low osmolalities and a negative inotropic effect at perfusate osmolality greater than 320 mOsm.litre-1.