Platelet-activating factor (PAF) has no direct effect on rat intracerebral arterioles in vitro.

We examined the effect of platelet activating-factor (PAF) on lumen diameter of penetrating intracerebral arterioles (diameter less than 50 microns) dissected from rat brains. PAF over a concentration range of 10(-12)-10(-6) M had no effect on lumen diameter. However, the arterioles were capable of both vasodilation in response to calcitonin gene-related peptide (EC50 = 4.4 nM) and vasoconstriction in response to the thromboxane mimetic, U44619 (EC50 = 5.8 nM). We conclude that the effects of PAF on the cortical circulation observed in vivo are indirect and may be due to PAF-induced changes in other humoral or cellular mediators.