I really wish I could comment on this with confidence. But I don't know anything about injecting pgf2a. I would guess that either you are setting yourself up for potent, yet probably painful gains. Or you might be doing something dangerous. Maybe I'll find some time to look into pgf2a injectables or email Bill about this.
BTW, arachidonic acid is not a prostaglandin but a precursor to one... which is probably what you meant.
For now, I would err on the safe side and use them separately.