Characterization and longitudinal monitoring of serum progestagens and estrogens during normal pregnancy in the killer whale (Orcinus orca)

- P4 is the dominate progestagen in the luteal phase and pregnancy in killer whales.
- Maternal recognition of pregnancy occurs between 21 and 28 day post conception.
- 5α-DHP is the major progesterone metabolite during luteal phase and pregnancy.
- 5α-DHP is the major progestagen in placental cord blood at birth.
- Both E1-C and E2 increased in LATE pregnancy and E2 was affected fetal sex.

The secretory patterns of progestagens and estrogens were characterized throughout 28 normal pregnancies until two month post-partum in eleven killer whales. HPLC analysis of serum from different reproductive stages (luteal phase, EARLY, MID, and LATE pregnancy) identified three major immunoreactive progestagen peaks; progesterone (P4), 5α-pregnane-3,20-dione (5α-DHP) and pregnanediol, with 5α-DHP approximately half of that for P4 in the luteal phase, and EARLY, but approximately 2/3 of P4 during MID and LATE pregnancy. At birth, 5α-DHP was the only significant (>10% immunoreactivity) immunoreactive progestagen detected in placental (umbilical cord) serum. Maternal recognition of pregnancy appears to occur between day 21 and 28 post-ovulation when a significant deviation in progestagen concentrations between conceptive and non-conceptive cycles was detected. Progestagen concentrations during pregnancy displayed a bimodal pattern with significant peaks (P < 0.05) in EARLY (indexed month post-conception [IMPC] 2, 3, 4) and MID (IMPC 9, 10) before decreasing (P < 0.05) over an 11 day interval to luteal phase concentrations on the day of parturition. Among estrogens, estriol was secreted in the highest concentrations but only estrone (free and conjugated) and estradiol increased (P < 0.001) during pregnancy, with peaks observed during the final month of gestation, and an influence (P < 0.05) of fetal sex on estradiol production was detected. Collective findings indicate that P4 derived from the corpus luteum is the major biologically active progestagen during the luteal phase and pregnancy, and that 5α-DHP production, possibly from both luteal and placental sources, increases during the second half of pregnancy.