Evidence that prednisolone is inhibitory to the cyclooxygenase activity of human rectal mucosa.

The effect of prednisolone on prostaglandin (PG) synthesis by rectal biopsies in organ culture was investigated using laminary flow bioassay and radioimmunoassay (RIA) or PGE2. Prednisolone was consistently found to inhibit basal synthesis in cultures whose duration ranged from 2-40 hours. This appeared to be both time and dose dependent. The ability of biopsies homogenised at the end of culture to transform exogenous arachidonic acid into PGE2 under defined conditions was also investigated and operationally designated cyclooxygenase activity. Prior treatment with prednisolone resulted in a reduction in cyclooxygenase activity. This inhibition occurred with a longer latency and to a lesser extent than inhibition of overall basal synthesis. These results suggest that corticosteroids, in addition to their know (indirect) inhibitory action on phospholipase activity, also affect cycloooxygenase activity. The most likely mechanism are either a repression of synthesis of fresh cyclooxygenase enzyme of induction of an endogenous inhibitor of cyclooxygenase activity.