Effects of 17β-estradiol on the uterine luteolytic cascade in bovine females at the end of diestrus

In cattle, 17 beta-estradiol (E2) is essential for triggering luteolysis via the synthesis of prostaglandin F2 alpha (PGF2 alpha). We aimed to evaluate the effects of E2-treatment on day 15 of the estrous cycle on the transcript abundance of genes involved in the PGF2 alpha synthetic cascade. Nelore heifers (N = 50) were subjected to a hormonal protocol for the synchronization of ovulation. Between days 14 and 23 after estrus, the area (cm(2)) and blood perfusion (%) of the corpus luteum (CL) and progesterone (P4) plasma concentrations were evaluated daily. On day 15, the heifers were assigned to the Control (2 mL of pure sesame oil, N = 21) or Estradiol group (1 mg of E2 diluted in 2 mL of sesame oil, N = 23). After the treatments at 0 h, uterine biopsies were collected at times 1.5 h (C1.5h, N = 8 and E1.5h, N = 10) or 3 h (C3h, N = 8 and E3h, N = 11); and blood samples were obtained from 0, 3, 4, 6 and 7 h for the measurement of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) concentrations by ELISA. Transcript abundance was determined by RT-qPCR and protein abundance of ESR beta and OXTR was determined by Western Blotting. The Estradiol group showed greater (P < 0.05) concentrations of PGFM at 6 and 7 h compared to the Control group. A progressive decrease in plasma P4 concentrations characterized a hastened functional luteolysis, followed by structural luteolysis in the Estradiol group (P < 0.05). Among the treatment groups, no significant difference was detected for the abundance of PRKC alpha, PRKC beta, AKR1B1, PTGS2 and ESR alpha transcripts (P > 0.05). Estradiol treatment decreased the abundance of PLA2G4A, AKR1C4, and ESR beta both 1.5h and 3h after treatment (P < 0.05). The relative expression of PGR and OXTR was greater in E3h compared to the C3h (P > 0.05). Protein abundance did not differ between treatment groups at either experimental times (P > 0.05). Overall, E2 promoted an increase in PGFM concentrations and the hastening of functional and structural luteolysis in Nelore heifers through the upregulation of PGR and OXTR, demonstrating for the first time that the expression of these receptors within 3 h after E2 stimulus was associated with triggering luteolysis in cattle.

Automated summary

The study evaluated the effects of E2 treatment on Nelore heifers on day 15 of the estrous cycle, finding that E2 promoted an increase in PGFM concentrations and accelerated functional and structural luteolysis by upregulating the expression of PGR and OXTR. This suggests that within 3 hours after E2 stimulus, the expression of these receptors is associated with triggering luteolysis in cattle.