Effect of multiple low-dose PGF 2 α injections on the mature corpus luteum in non-pregnant bitches.

This study investigated molecular regulation in the canine corpus luteums/corpora lutea (CL) following multiple low-dose prostaglandin F ₂ alpha (PGF ₂ α) injections in non-pregnant bitches around 30-35 days after ovulation. The CL were obtained by ovariohysterectomy 1 h after the last PGF ₂ α injection. The subjects were divided into the following groups: control (no PGF ₂ α injection, n = 4), one PGF ₂ α injection (injection at 0 h, 1PGF, n = 4), two PGF ₂ α injection (injection at 0 and 8 h, 2PGF, n = 4), and three PGF ₂ α injection (injection at 0, 8 and 24 h, 3PGF, n = 4). In the 1PGF group, the steady-state mRNA levels of an immediate early gene (NR4A1) and immune system-related genes (MCP-1 and IL-8) increased. NR4A1 was localized in luteal and endothelial cells. In contrast, MCP-1 was localized in the luteal tissue between the luteal and endothelial cells. LHCGR, CYP11A1, and StAR mRNA expression decreased after the second PGF ₂ α injection. FASLG increased only after the third PGF ₂ α injection. The mRNA levels of PTGFR, PGT, and PTGS2 decreased as the number of PGF ₂ α injections increased. Immunohistochemistry showed a decrease in StAR protein density as the number of PGF ₂ α injections increased. BAX and CASP3 mRNA expression levels were similar among the groups. Serum progesterone (P ₄ ) levels decreased dramatically after the PGF ₂ α injections but were still higher than the basal level at the end of the study. In conclusion, repeated low-dose PGF ₂ α injections could induce luteolytic mechanisms in the CL of non-pregnant bitches. Furthermore, it can be concluded that, in non-pregnant bitches, some aspects of the molecular regulation of luteolysis in the CL are similar to some aspects of such regulation in other domestic animals.
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