Abstract
Low concentrations of several emetic, purgative or irritant drugs in the absence of added co-factors stimulated conversion of arachidonic acid to prostaglandin E2 and F2alpha by prostaglandin synthetase extracted from bull seminal vesicles (BSV prostaglandin synthetase). Their effect was dependent on concentration and time. Stimulation of BSV prostaglandin synthetase by apomorphine, aloes, tyramine or zingerone was increased several-fold by addition of reduced glutathione to the incubation medium, whereas hydroquinone, a phenolic co-factor of prostaglandin synthetase caused slight depression. From this finding and from the observation that many of the stimulant drugs possess a phenolic group, whereas their inactive relatives lack such a group, it is suggested that these stimulant drugs act as co-factors for prostaglandin synthetase in place of hydroquinone. Aloes, tyramine, ethanol and quipazine also produced a dose-related increase in resting tone of the isolated fundus of the rat stomach. This increase occurred at concentrations comparable to those effective in stimulating BSV prostaglandin synthetase, and was abolished by acetylsalicylate. These findings support the view that certain drugs exert some of their pharmacological effects by stimulating prostaglandin synthetase.