The role of dopamine D2 receptor in the maintenance of pregnancy

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Luteinization hormone and prolactin secreted by pituitary play an important role in the maintenance of luteal function especially at early pregnancy. It is well known that dopamine agonist (dopamine D2 receptor stimulant) is able to inhibits prolactin release from the pituitary gland. To study the role of dopamine D2 receptor in the maintenance of luteal function and pregnancy, we investigated the effect of cabergoline (CAB), a long-acting dopaminergic agonist , on the steroidogenesis of cultured rat granulosa cells and porcine luteal cells. Also the expression of dopamine D2 receptor mRNA in the mouse ovary was examined by RT-PCR. CAB inhibited the FSH-stimulated production of progesterone by cultured rat granulosa cell at concentrations ranging from 10ィイD1-8ィエD1 to 10ィイD1-4ィエD1M. At high concentrations (10ィイD1-5ィエD1 and 10ィイD1-4ィエD1M), CAB inhibited the production of estradiol by cultured rat granulosa cell. The production of progesterone by cultured luteal cell prepared from porcine corpus luteum was also inhibited by CAB at concentrations ranging from 10ィイD1-8]ィエD1 to 10ィイD1-4ィエD1M in the both condition with or without LH.Ovary from control, under inducing (48 h after injection of PMSG), preovulatory (6h after injection of hCG), ovulatory (12h after injection of hCG), postovulatory(24 and 48 h after injection of hCG) mice was examined for the expression of dopamine D2 receptor mRNA. However, the message of dopamine D2 receptor was not detected in the ovary at any ovulatory cycle These results, that dopamine D2 receptor stimulant directly inhibits the steroidogenesis of granulosa cells and luteal cells in vitro, suggest that dopamine D2 receptor may participate in the maintenance of luteal function and pregnancy.