The effect of sodium meclofenamate on the binding of [3H]prostaglandin E2 [( 3H]PGE2) to membranes from human myometrium was investigated. Meclofenamate inhibited the binding of [3H]PGE2 to high-affinity (dissociation constant 1.5 nmol/l) sites in a reversible dose-dependent manner (inhibition constant 11 mumol/l). The mechanism of inhibition was mainly competitive, but at high doses of meclofenamate (greater than or equal to 100 mumol/l) there was loss of PGE receptor sites. Of several PG synthesis inhibitors tested, only meclofenamate and, to a lesser extent, mefenamic acid had a significant inhibitory effect. PGE2 stimulated cyclic AMP generation in slices of human myometrium and this was inhibited by meclofenamate in a dose-dependent manner (50% inhibition occurred at 9 mumol/l). Again, this effect was specific for meclofenamate and fitted a competitive mechanism at doses in the range 1-10 mumol/l and a non-competitive mechanism at higher doses. The data show that meclofenamate, in addition to its traditional role as a PG synthesis inhibitor, affects directly PGE receptor binding and activation.

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