Dopamine D 2 receptor-induced COX-2-mediated production of prostaglandin E 2 in D 2-transfected Chinese hamster ovary cells without simultaneous administration of a Ca 2+-mobilizing agent

Abstract

We have earlier demonstrated that dopamine stimulates the liberation of the prostaglandin E 2 (PGE 2) precursor, arachidonic acid, in Chinese hamster ovary cells transfected with the rat dopamine D 2 receptor (long isoform), also without concomitant administration of a Ca 2+-releasing agent [Nilsson et al., Br J Pharmacol 1998;124:1651–8]. In the present report, we show that dopamine, under the same conditions, also induces a concentration-dependent increase in the production of PGE 2, with a maximal effect of 235% at ∼100 μM, and with an ec 50 of 794 nM. The effect was counteracted by the D 2 antagonist eticlopride, pertussis toxin, the inhibitor of intracellular Ca 2+ release TMB-8, incubation in Ca 2+-free experimental medium, and PKC desensitization obtained by chronic pretreatment with the phorbol ester TPA. It was also antagonized by the non-specific cyclooxygenase (COX) inhibitor, indomethacin, and by the selective COX-2 inhibitor, NS-398, but not by the specific COX-1 inhibitor, valeryl salicylate. Both the non-specific phospholipase A 2 inhibitor, quinacrine, and an inhibitor of cPLA 2 and iPLA 2, AACOF3, counteracted the effect; in contrast, a selective iPLA 2 inhibitor, BEL, and a selective sPLA 2 inhibitor, TAPC, were ineffective. No effects of dopamine were obtained in control cells mock-transfected with the p3C vector only. The results reinforce previous assumptions that dopamine may interact with eicosanoid metabolism by means of D 2 receptor activation, and implicate an involvement of cPLA 2 and COX-2 in this effect. It is suggested that measurement of dopamine-induced PGE 2 production may serve as a convenient way to study D 2 receptor function in vitro.