ENHANCEMENT OF CARDIAC-PERFORMANCE OF ISOLATED WORKING GUINEA-PIG HEART BY RABBIT PLATELET AND INVOLVEMENT OF HISTAMINE

Alterations of cardiac performance by washed rabbit platelets were inv estigated in isolated working guinea pig hearts. Enhanced cardiac func tions emerged about 5 s after intracardiac injection of platelet suspe nsion (6 X 10(8) - 10 X 10(8) cells . ml-1). The LVP, +dP/dt(max), -dP /dt(max), and HR were increased by 30%, 73%, 46%, and 13% (P<0.05 or 0 .01), respectively, and recovered about 10 min later. In the range of 1 X 10(8) - 70 X 10(8) cells . ml-1, platelet suspension strengthened the cardiac performance in a concentration-dependent manner. The super natant demonstrated positive inotropic and chronotropic effects as wel l, quite similar to those of the suspension. Cimetidine (Cim, 1 mumol . L-1) reduced the cardiotonic effect of the platelet. Mast cell of th e isolated guinea pig heart was proven to be in an activated state upo n 10(9) cells . ml-1 platelet challenge by electron microscopy. Histam ine content in platelet suspension measured by HPLC was shown to be 2. 6 +/-s 0.7 mug per 10(9) platelets. It is concluded that histamine, re leased from platelets and cardiac mast cells, was a key factor in the cardiac alterations.