Effects of bromocriptine on PGF_2α fluctuation in corpus luteum of pseudo-pregnant rats

To study a possible physiological role of luteal PGF_2α , we measured PGF_2α fluctuation, levels and metabolic activity(MA), in the corpus luteum(CL) during pseudopregnancy(PSP) and when PSP was interrupted by a single injection of bromocriptine (BC, an inhibitor of prolactin secretion). PSP was induced by mating with vasectomised male rats. At 08：00 on the indicated days of PSP or at 0, 12 and 24hr after injection of BC on day 6 of PSP, blood was collected and CL removed. Serum progesterone levels and luteal PGF_2α fluctuation were measured. The luteal PGF_2α levels were low during the midluteal phase, and increased towards the end of PSP. Conversely, luteal PGF_2α -MA was high during the midluteal phase, and gradually declined during the late luteal phase. By 24hr after injection of BC, luteal PGF_2α levels increased significantly, with a reciprocal reduction in serum progesterone levels and luteal PGF_2α -MA. These results suggest that luteolysis is caused by an increase in luteal availability of PGF_2α and that increment in PGF_2α levels may be related to the decline in PGF_2α -MA.