220 Hormonal profiles of bovine follicular fluid during the window of in vivo oocyte maturation
S. Salman A B , O. Gungor A C , S. Ranjitkar A , D. Zhang A and E. Oberhaus DA University of Connecticut, Storrs, CT, USA
B University of California, Davis, Davis, CA, USA
C Bolu Abant Izzet Baysal University, Bolu, Turkey
D Louisiana State University, Baton Rouge, LA, USA
Reproduction, Fertility and Development 35(2) 239-239 https://doi.org/10.1071/RDv35n2Ab220
Published: 5 December 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Bovine follicular fluid is the microenvironment that supports oocyte maturation and competence. Follicular hormones undergo drastic changes during maturation, yet their levels have not been systematically characterised under precise and controlled experimental timing. We determined follicular oestradiol and progesterone and the ovarian structures during this maturation window. Holstein heifers (n = 30) were synchronised in a modified 7-day CIDR synchronisation protocol as following: two sets of two PGF2α (PG) injections on Days −11 and 0, CIDR during Day −6 to Day 1, and one gonadotrophin-releasing hormone (GnRH) injection on Day 2. Daily ultrasonography and jugular blood sampling were conducted to characterise ovarian development and synchronisation effectiveness. Animals were randomly assigned to one of five groups (n = 6), and ovaries were collected at 24 h, 48 h, 60 h, 72 h, and 78 h post-second-set of PG. Statistical analysis of two-way ANOVA was used for CL and secondary follicle presence, and largest follicle size effect on hormones. Also, Fisher’s (l.s.d.) pairwise analysis to compare between groups, Pearson coefficient to correlate the hormones across time points and ovarian response parameters, and significance were set at (P < 0.05). The effect of CIDR removal showed a rapid decline in serum progesterone levels at 48 h after PG at 0.21 ± 0.04 ng/mL when compared to 24 h levels at 3.51 ± 0.17 ng/mL, demonstrating the effectiveness of the modified 7-day CIDR synchronisation. The sizes of the largest follicles increased significantly with time after PG (P = 0.037) as expected. Neither the total luteal volumes nor total follicular volumes were affected after PG (P > 0.05). Interestingly, the largest follicle size was affected by the presence of CL on the same ovary (P = 0.002). Follicular fluid oestradiol concentrations in the largest follicles measured as high as 1323.6 ng/mL and mean of 775.9 ± 155.2 ng/mL at 24 h after PG, demonstrating the hallmark trait of dominant and preovulatory follicles. Follicular fluid oestradiol concentrations declined after PG, showing a downward trend leading to ovulation, and reached the lowest level of 225.2 ± 76.7 ng/mL at 78 h after PG (P = 0.005). The opposite took place for follicular progesterone, which was 88.5 ± 17.7 ng/mL at 24 h and 168.34 ± 23.3 ng/mL at 78 h, showing an upward trend leading to ovulation (P = 0.001), especially during the 48–72 h window. Follicular oestradiol levels were not affected by subordinate follicle presence on the same ovary (P > 0.05). Interestingly, follicular oestradiol was affected by CL presence (P = 0.037) and by the largest follicle size across time points after PG (P = 0.014). Furthermore, follicular progesterone levels were neither affected by CL presence nor the largest follicle size (P > 0.05) but were affected by subordinate follicle presence on the same ovary (P = 0.034). Follicular oestradiol was negatively correlated with follicular progesterone when blocked by time points after PG (P = 0.019), but with a considerably low R2 value at 0.28, indicating high variations among animals. In conclusion, follicular fluid oestradiol decreased and progesterone increased during the window of oocyte maturation, likely due to the effect of the LH surge induced by GnRH.
