Platelet activating factor (PAF), a potent
lipid-like vasoactive agent, induced rat foot
edema when it was injected subplantarly. The
edema reached its maximum 1 h after PAF challenge.
Indomethacin did not inhibit the peak edematous response whereas both PAF antagonists,
kadsurenone and
L-652,731, inhibit the PAF-induced rat foot
edema (PFE). Both PAF antagonists also partially block the first phase of the
carrageenin-induced rat foot
edema (CFE). Using the inhibition of [3H]PAF receptor binding to prepared rabbit platelet membranes, release of PAF or PAF-like materials in
carrageenin-injected rat hindpaw was observed. These results suggest that the released PAF or PAF-like materials together with the released
histamine and
kinin evoke the first phase hindpaw
edema in the rats.
Indomethacin or PAF antagonist, administered alone, does not block the first phase or the second phase of CFE, respectively. However, PAF antagonist potentiated the inhibitory effects of
indomethacin suggesting that the released PAF may also be involved in the biosynthesis of
prostaglandins to initiate the second phase of rat CFE.