Estradiol has a major role in antrum formation of porcine preantral follicles cultured in vitro.

Antrum formation and estradiol (E2) secretion occur during early folliculogenesis. The objective was to determine the role of E2 in antrum formation of oocyte-granulosa cell complexes (OGCs) derived from porcine preantral follicles (PAFs). Supplementation of the culture medium with E2 (1 µg/mL) improved antrum formation of OGCs during 14 days of in vitro culture. Furthermore, adding 0.1 µg/mL androstenedione (a precursor of E2) to the medium also improved antrum formation. Concentration of E2 was higher in the medium of developmentally competent OGCs versus incompetent OGCs (8.5 vs. 3.5 ng/mL, P < 0.05). Fulvestrant (1 µg/mL), a competitive inhibitor of E2, completely inhibited antrum formation of OGCs that were cultured in medium containing either E2 (0.1 µg/mL) or androstenedione (0.1 µg/mL); however, increasing E2 to 1 µg/mL ameliorated the inhibitory effect. Conversely, in the case of early antral follicles, OGCs formed antrums without E2 supplementation. After E2 pretreatment, OGCs derived from PAFs formed antrums even when the OGCs were subsequently cultured in medium without E2. Furthermore, when OGCs derived from PAFs were cultured without E2 followed by an additional in vitro culture with E2, antrums were formed, albeit with the same period delay by the same pretreatment periods. In conclusion, E2 in the culture medium was indispensable for in vitro antrum formation of OGCs derived from PAFs; therefore, one of the roles of E2 is in the initiation of antrum formation.

Effect of N-acetyl-D-glucosamine on bovine sperm-oocyte interactions.

N-Acetyl-D-glucosamine (GlcNAc) is a major component of glycosaminoglycan, which is involved in sperm-oocyte interactions. We examined the effect of adding GlcNAc and other monosaccharides, D-mannose and D-fucose, to the in vitro fertilization (IVF) medium on bovine sperm-oocyte interactions. In medium in which sperm and a zona pellucida (ZP) were co-incubated with monosaccharides for 5 min, addition of GlcNAc (5 or 25 mM) significantly reduced the number of sperm that attached to the ZP. Pretreatment of gametes with GlcNAc (5 mM) prior to co-incubation also suppressed sperm-ZP attachment. Addition of GlcNAc (5 or 25 mM) to the medium in which sperm and a ZP were co-incubated for 5 h, however, significantly increased the number of sperm binding to and penetrating the ZP in a concentration-related manner. The other monosaccharides, D-fucose and D-mannose, did not have this effect. Supplementation of the sperm-oocyte co-incubation medium with 5 mM GlcNAc also enhanced the rate of polyspermic fertilization. When the ZPs were removed from the oocytes, GlcNAc did not affect the fertilization rate. Furthermore, incubation of sperm with 5 mM GlcNAc induced sperm membrane destabilization and an acrosome reaction, as evidenced by the hypo-osmotic swelling test and fluorescein isothiocyanate-labeled peanut agglutinin/propidium iodide (FITC-PNA/PI) staining. Finally, GlcNAc suppressed ZP hardening following fertilization, as determined by measuring the time required for pronase to dissolve the ZP. In conclusion, supplementation of IVF medium with GlcNAc has various effects on sperm-oocyte interactions including suppression of initial attachment, induction of sperm membrane destabilization and acrosome reaction, increase in the number of sperm secondarily bound to and penetrating the ZP, suppression of ZP hardening following sperm-oocyte co-incubation and increase in the rate of polyspermic fertilization.