PGE2 concentration of the follicular fluid as a measure of heterogeneity of the response to hormonal stimulation of the bovine ovarian follicle
Résumé
The LH surge promotes prostaglandin E2 (PGE2) production within the preovulatory follicle. Oocyte
microenvironment levels of PGE2 affect the developmental competence after fertilization. This study
aimed to characterize the follicular fluid PGE2 enrichment during superovulation treatment. Six heifers
(Holstein, 20.3 +/-0.85 months old) received FSH (Stimufol®, Reprobiol, Belgium): half dose, ie, 250 μg
of porcine follitropin (pFSH), combined with 50 μg of porcine lutropin (pLH). At the rate of 8 injections,
in degressive dose, spread over 4 days. PGF2α (Estrumate®, MSD Santé Animale, France) was injected
at the same time as the 5th injection of Stimufol®.LH peak was assumed to occur between 35 and 40
hours after the PGF2α injection. Individual sampling of fluid from antral follicles was performed by
ovum pick up 12 hours before PGF2α injection and 60 hours after PGF2α injection. This protocol was
designed to allow the collection of fluids from ovarian follicle containing either a pre-matured or a
matured oocyte. Each heifer was his own control as we took the "pre-matured" follicular fluid on a first
ovary and the "matured" follicular fluid on the 2nd ovary, 3 days later. The punctures were repeated
twice and were cross-checked for the next repetition to evaluate the impact of the ipsi or contralateral
side of the corpus luteum (CL) on the follicular fluid composition. The volume of fluid was measured for
each punctured follicle. The PGE2 concentration of the follicular fluid was measured by Elisa (Cayman
Chemical) to determine the progress of terminal follicular differentiation. An average of 13 +/- 5.06 and
28 +/-13.9 follicles were punctured per session/heifer for respectively pre-matured (n=78) and matured
(n=169) follicles. The mean collected volume differed between the two groups (pre-matured: 0.229+/-
0.213 ml/follicle; matured: 0.575+/-0.379 ml/follicle; two samples t-test, pval<0.0001). No effect of the
side of CL on fluid volume was detected (2-way Anova, p=0.397). The PGE2 concentration was
determined in 25 pre-matured follicles and 127 matured follicles. The mean PGE2 concentration
significantly differed between the two groups of follicular fluids (pre-matured: 7.2 +/-7.5 ng/ml; matured:
60.2 +/-58.6 ng/ml) No effect of the side of CL was detected (p=0.278). Surprisingly, there was no linear
relationship between fluid volume and PGE2 concentration (adjusted R-squared: -0.0002, pvalue=0.327). PGE2 concentrations were very spread out within the matured group. This important
dispersion (Interquartile range=58.6 ng/ml) indicated that despite follicle growth in response to hormonal
stimulation (FSH/LH) the ability of follicular granulosa and cumulus cells to synthesize PGE2 was
imperfectly achieved. Only 48% of the follicular fluids in the mature group had higher PGE2 levels than
those in the premature follicle group. In conclusion, despite the ability of the stimulation treatment to
promote growth of many follicles, there was a great heterogeneity in terms of PGE2 synthesis. This
alteration could represent defective signaling mechanisms that could impact the developmental
competence of the oocyte.
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