Coronary vascular response to platelet-activating factor in the perfused rat heart

The coronary vascular responses to platelet-activating factor (PAF) were studied in isolated perfused rat hearts. Constant flow rates were maintained and the changes in perfusion pressure were recorded following bolus injections of PAF. The effect of PAF on the perfusion pressure was variable and depended on certain conditions. Firstly, when the starting baseline pressure was 65-75 mm Hg, bolus injections of PAF resulted in an initial decrease followed by an increase in perfusion pressure. However, the decrease in perfusion pressure was less pronounced when the starting baseline pressure was 40 mm Hg. Secondly, the response varied with the amount of PAF that was injected. Injections of 10 fmol-1 pmol of PAF prepared in a solution containing bovine serum albumin resulted in decreases in perfusion pressure that were not followed by increases. A biphasic response, consisting of an initial decrease followed by an increase in perfusion pressure, was observed following injections of 10 and 100 pmol of PAF. Only increases in perfusion pressure were recorded following injections of 1000 pmol of PAF. Thirdly, the response to injection of PAF was dependent on whether it was prepared in a solution containing serum albumin. This study demonstrates that it is possible to observe vasodilation, vasoconstriction and biphasic responses to PAF in the isolated rat heart model.