Ulcerative colitis: effect of sulphasalazine, its metabolites and indomethacin on the ability of human colonic mucosa to metabolize prostaglandins in vitro.

1 Homogenates of mucosa from human colon metabolize [3H]-prostaglandin E1 in the presence of nicotinamide adenine dinucleotide to 15-oxo prostaglandin E1 or 15-oxo, 13,14 dihydro prostaglandin E1. 2 Metabolic capacity of tissue from patients with active ulcerative colitis under treatment with sulphasalazine (0.021 +/- 0.004 nmol/Mg protein +/- s.e. mean) did not differ from mucosa of normal patients (0.02 +/- 0.004 nmol/mg protein) during 1 h incubation. 3 Sulphasalazine inhibits prostaglandin E1 metabolism by mucosal homogenates in a dose-dependent manner with an ID50 of 125 microM. Its therapeutically active metabolite, 5-aminosalicylic acid (2.6 mM) was without significant inhibitory activity. 4 Indomethacin inhibits prostaglandin E1 metabolism by colonic mucosa with an ID50 of 388 microM. 5 At present we cannot clearly relate the therapeutic benefit of sulphasalazine and its therapeutically active metabolite, 5-aminosalicylic acid, in ulcerative colitis to their effects on prostaglandin E synthesis or metabolism in vitro.