Interaction of rioprostil with the parietal cell prostaglandin E2 receptor

The interaction of rioprostil with the porcine parietal cell prostaglandin (PG) E2 receptor and with uterine 3H-PGE2 binding sites was investigated. The in vitro antisecretory effect was measured by the inhibition of histamine stimulated 14C-aminopyrine uptake in isolated pig parietal cells. Rioprostil displaced 3H-PGE2 competitively from the porcine fundic PGE2 receptor and had 1/25 of the affinity (Kd = 8 X 10(-8) mol/l) of the natural ligand; it was, however, equipotent with the synthetic prostacyclin analogue, iloprost. Similar affinity ratios were found in uterine muscle. Rioprostil inhibits parietal cell acid production with an IC50 in the range of its gastric binding dissociation constant. It is concluded that rioprostil exerts its antisecretory effects via a parietal cell E-type receptor. The compound cannot discriminate between fundic and uterine 3H-PGE2 binding sites with as yet unknown functional implications.