PARENT SESSION
Oocyte Development

EFFECT OF MONO-(2-ETHYLHEXYL) PHTHALATE ON BOVINE OOCYTE MATURATION IN VITRO.

Anas, Idris¹, Suzuki, Chie¹, Iwamura, Shokichi¹, Yoshioka, Koji¹, ¹

ABSTRACT- Di-(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer known to adversely affect the reproductive system of animals. The present study was undertaken to examine the effect of different doses of mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of DEHP, on bovine oocyte maturation in vitro. Cumulus-oocyte complexes (COCs) were cultured in a humidified atmosphere of 5% CO₂ at 39°C for 24 h in a basic medium(TCM+Na pyruvate+FSH+PVP+Gentamycin) containing 0, 10, 25, 50, 75 and 100 M MEHP. Oocytes were then denuded, fixed and stained with orcein for the assessment of the stage of maturation. The number of oocytes remained at the germinal vesicle (GV) stage was significantly (P<0.05) higher with 75 and 100 M treatments than the control. The proportion of oocytes that reached metaphase II (MII) stage of maturation was significantly (P<0.05) decreased with 50, 75 and 100 M concentration of MEHP in comparison to the control. When denuded oocytes were used, none of them has progressed to MII stage of maturation in the presence of 50, 75 or 100 M MEHP. The percentage of denuded oocytes remaining at the GV stage was significantly (P<0.05) increased with 50, 75 and 100 M MEHP treatments. To examine the reversibility of the inhibitory effect of MEHP, COCs were cultured for 24 h with 50 or 100 M of MEHP before been transferred to the basic medium and cultured for more 24 h. When 50 uM was used, only 0.8 % of the cultured oocytes were at the GV stage whereas 71% of them reached the MII stage. For the 100 M treatment, 1.9% and 65.7% of the oocytes were at the GV and MII stages after the second period of maturation. These results indicate that MEHP can reversibly inhibit bovine oocyte maturation in vitro.

KEY WORDS: MEHP, bovine, oocyte, maturation