Effects of estradiol-17β and progesterone supplementation on in vitro nuclear maturation of canine oocytes

Unlike in other domestic animals, in vitro maturation (IVM) of canine oocytes has had limited success. The present study investigated the effect of the estrous cycle and estradiol-17β (E2) or progesterone (P4) supplementation on in vitro nuclear maturation of canine oocytes recovered from domestic dog ovaries in various reproductive states (follicular, luteal or anestrous stages). Oocytes were cultured in serum-free tissue culture medium (TCM)-199 supplemented with various concentrations of E2 (Exp. 1: 0, 0.1, 1.0 or 2.0 μg/ml) or P4 (Exp. 2; 0, 0.5, 1.0 or 2.0 μg/ml) for 72 h to determine the effective concentration of hormones. In Exp. 3, in order to investigate the synergistic effect of E2 and P4 supplementation, three groups of oocytes were cultured with 2 μg/ml E2 plus various concentrations of P4 (0, 0.5, 1.0 or 2.0 μg/ml). As results, the rate of maturation to metaphase II (MII) stage was significantly higher (P < 0.05) in oocytes from the follicular stage supplemented with 2 μg/ml E2 (14.7%) compared to the other groups (1.5-8.2%). Significantly higher (P < 0.05) maturation rate to MII stage was observed in oocytes from the follicular stage supplemented with 1.0 (10.0%) or 2.0 μg/ml (10.8%) P4 compared to the other groups (0-4.8%). Furthermore, more (P < 0.05) oocytes from the follicular stage supplemented with 2.0 μg/ml of E2 and P4 (16.6%) were matured to MII stage compared to oocytes from the follicular stage supplemented with 2.0 μg/ml E2 alone (10.4%) or the other groups of oocytes (0-7.8%). Interestingly, compared to 2.0 μg/ml E2 alone (10.4%), supplementation of 2 μg/ml E2 + 0.5 μg/ml P4 (3.4%) decreased the maturation of oocytes from the follicular stage to MII stage. In conclusion, the present study demonstrated that supplementation of the culture medium with E2 or P4 alone significantly increased maturation of canine oocyte to MII and that P4 supplementation with E2 further promote or decrease oocyte maturation compared to E2 alone depending on P4 concentration.