Endogenous activation of prostaglandin synthesis in rabbit colonic explants cultured in vitro

Rabbit colonic biopsy specimens cultured in vitro showed an optimal release of prostaglandin E2 (PGE2) after 6-7 h of incubation. The amplitude but not the PGE2 production profile was dependent on stimuli applied--that is, A23187 greater than phorbol 12-myristate 13-acetate greater than control. This study was undertaken to determine the nature of this time-dependent optimum. The following hypotheses were tested: increased substrate availability, de novo synthesis of prostaglandin synthetase (PS), and translocation of PS or increased activity of PS. Arachidonic acid, either continuously present or given as a pulse, increased the overall amplitude equally but did not change the production profile. Cycloheximide, 0.2 microM, which inhibited 50% of the protein synthesis, increased the PGE2 production by 80% at 7 h. The cytoskeletal disrupting agent cytochalasin B had no effect. Homogenates of specimens cultured 6 h showed an increased PGE2 production. This was partly explained by a large increase in the PGE2 production capacity of the particulate matter obtained after 45 min of centrifugation at 100,000 g. It is concluded that the PGE2 production peak is due to an activation of preformed PS and that the PS activity is under the control of a peptide inhibitor, dependent on protein synthesis.