Paracetamol potentiates acetylsalicylate in inhibiting prostaglandin synthesis.

Lower concentrations of paracetamol stimulated, but a higher concentration inhibited prostaglandin synthesis by bull seminal vesicle homogenate in the absence of added co-factors. Admixed with acetylsalicylate or indomethacin, paracetamol strongly potentiated the inhibition of prostaglandin synthesis in vesicle homogenate, and weakly potentiated inhibition in rat gastric fundus strip. We propose that, by acting as a phenolic co-factor, paracetamol stimulates prostaglandin synthesis and thus renders the cyclo-oxygenase more vulnerable to acetylsalicylate or indomethacin.