Interaction of Rioprostil with the Parietal Cell Prostaglandin E₂ Receptor

Abstract

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 × 10⁻⁸mol/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.

Key Words:

• Antisecretory effect
• porcine parietal cells
• prostaglandin E₂ receptor
• rioprostil
• uterine binding sites