Effect of multiple low-dose PGF2α 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 F2 alpha (PGF2α) injections in non-pregnant bitches around 30–35 days after ovulation. The CL were obtained by ovariohysterectomy 1 h after the last PGF2α injection. The subjects were divided into the following groups: control (no PGF2α injection, n = 4), one PGF2α injection (injection at 0 h, 1PGF, n = 4), two PGF2α injection (injection at 0 and 8 h, 2PGF, n = 4), and three PGF2α 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 PGF2α injection. FASLG increased only after the third PGF2α injection. The mRNA levels of PTGFR, PGT, and PTGS2 decreased as the number of PGF2α injections increased. Immunohistochemistry showed a decrease in StAR protein density as the number of PGF2α injections increased. BAX and CASP3 mRNA expression levels were similar among the groups. Serum progesterone (P4) levels decreased dramatically after the PGF2α injections but were still higher than the basal level at the end of the study. In conclusion, repeated low-dose PGF2α 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.