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 from the corpus luteum (CL) and affects bovine fertility. However, the mechanism by which LBF affects fertility remains unclear. The present study was conducted to investigate the effects of LBF on endometrial P4 concentrations and gene expression. From 13 Japanese Black cows, endometrial biopsy and blood samples were collected after ultrasound examinations on Day 7 (Day 0 = the day of estrus). Based on the LBF, the 13 cows were divided into low (LV; n = 5), medium (MV; n = 2), or high vascularity (HV; n = 6) groups. The plasma and endometrial P4 concentrations were measured by enzyme immunoassay analysis. RNA sequencing was performed to compare the endometrial gene expression profiles of samples from three cows each in the LV and HV groups. Quantitative reverse transcription 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 the 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 with the LV group, the HV group presented higher CCN3 and PGR mRNA expression levels and lower ANPEP, DGAT2, and DKK1 mRNA expression levels. In conclusion, the results of this study show that LBF affects endometrial gene expression without changes in plasma or endometrial P4 concentrations on Day 7.