Cryoprotectant toxicity and cryopreservation success in IVF-derived domestic cat embryos after embryo transfer

Prostaglandin F2α (PGF2α) plays a role in the regression of the corpus luteum (CL) in a number of placental mammals. However, the mechanism of luteal regression has not been extensively studied in marsupials. The objectives of this study were to characterize changes in concentrations of PGF2α within utero-ovarian (UO) tissue/venous plasma during the luteal phase of the estrous cycle in Virginia opossums, to correlate these changes with those of plasma progesterone (P4), and to characterize the peripheral pattern of 13,14-dihydro-15-keto-PGF2α (PGFM) in parturient opossums. Ovaries, uteri, UO venous plasma and peripheral plasma were collected on Days 5, 9 and 12 after induced ovulation (n = 3 to 4 opossums/group). In addition, concentrations of PGFM were measured in peripheral plasma collected from two opossums during late gestation (Days 7,9,11 and 12) and at parturition (Day 13). Concentrations of P4, PGFM and PGF2α in tissue homogenates and plasma samples were estimated by radioimmunoassay. In nonpregnant opossums, peripheral P4 levels were highest on Day 5 (38.8 ± 11.1 ng/ml, x ± SEM) declined on Day 9 (22.6 ± 7.4 ng/ml), and were at basal levels by Day 12 (2.4 ± 0.7 ng/ml). Endometrial concentrations of PGF2α increased (P = 0.056) from Day 5 (15.7 ± 4.1 ng/g) to Day 9 (92.1 ± 61.0 ng/g) and were maintained to Day 12 (97.2 ± 25.7 ng/g). Prostaglandin F2α concentrations in UO plasma increased (P < 0.01) from Day 5 (143.1 ± 32.7 pg/ml) to Day 12 (333.0 ± 32.4 pg/ml). Prostaglandin F2α concentrations in ovarian tissue followed a similar pattern and were correlated with UO concentrations (r = 0.708, P < 0.05). In pregnant opossums, the highest levels of peripheral PGFM were recorded in the peripartum period, when luteal regression would also be expected to occur. The negative temporal relationship between peripheral concentrations of P4 and concentrations of PGF2α in UO tissue/venous plasma observed in this preliminary study is consistent with the notion that PGF2α from the ovary and/or uterus may play a role in CL regression in the opossum.