Enhancement of cardiac performance of isolated working guinea pig heart by rabbitplatelet and involvement of histamine

Alterations of cardiac performance by washed rabbit platelets were investigated in isolated working guinea pig hearts. Enhanced cardiac functions emerged about 5 s after intracardiac injection of platelet suspension (6 x 10(8)-10 x 10(8) cells.ml-1). The LVP, +dP/dtmax, -dP/dtmax, 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 supernatant demonstrated positive inotropic and chronotropic effects as well, quite similar to those of the suspension. Cimetidine (Cim, 1 mumol.L-1) reduced the cardiotonic effect of the platelet. Mast cell of the isolated guinea pig heart was proven to be in activated state upon 10(9) cells.ml-1 platelet challenge by electron microscopy. Histamine content in platelet suspension measured by HPLC was shown to be 2.6 +/- s 0.7 microgram per 10(9) platelets. It is concluded that histamine, released from platelets and cardiac mast cells, was a key factor in the cardiac alterations.