Effects of luteal blood flow on endometrial progesterone concentrations and gene expression in Japanese Black cows

Luteal blood flow (LBF) is essential for progesterone (P₄) biosynthesis in the corpus luteum (CL) and affects bovine fertility. However, the mechanism by which LBF affects fertility remains unclear. This study was conducted to investigate the effects of LBF on endometrial P₄ concentrations and gene expression. Endometrial biopsies and blood samples were collected from 13 Japanese Black cows after ultrasound examination on Day 7 (Day 0 = day of estrus). Based on LBF, the cows were divided into low- (LV; n = 5), medium- (MV; n = 2), and high-vascularity (HV; n = 6) groups. Plasma and endometrial P₄ concentrations were measured using enzyme immunoassays. RNA sequencing was performed to compare the endometrial gene expression profiles from three cows in each of the LV and HV groups. Reverse transcription-quantitative PCR was performed for genes selected from the differentially expressed genes (DEGs), P₄ receptors (PGR, PGRMC1, and PGRMC2), and P₄-regulated genes (ANPEP, DGAT2, DKK1, and LTF). No differences were observed in plasma or endometrial P₄ concentrations between the HV and LV groups. CCN3 was identified as a DEG between the HV and LV groups and was upregulated in the HV group. Compared to those of the LV group, the HV group exhibited higher CCN3 and PGR mRNA expression levels and lower ANPEP, DGAT2, and DKK1 mRNA expression levels. In conclusion, LBF affects endometrial gene expression without changing plasma or endometrial P₄ concentrations on Day 7.