Abstract

With the exception of gestational progesterone profiles^1-6 and to a lesser extent relaxin⁴ and thyroid hormones,⁷ the endocrinology of the pregnant bottlenose dolphin is poorly understood, especially with regards to estrogens, androgens, and glucocorticoids. A better understanding of the endocrine milieu throughout normal pregnancy can add to the species' reproductive database and may assist with the identification and clinical management of abnormal pregnancy. The overall goal of this study was to describe profiles of serum estrogens, testosterone and cortisol during normal pregnancy in bottlenose dolphins. Pools of bottlenose dolphin sera from estrus, early (EARLY: Days 0 to 120), mid (MID: Days 121 to 240), and late (LATE: Days 241 to parturition; Day 0 = day of conception) pregnancy were analyzed using high performance liquid chromatography. The predominant estrogens in all categories were estrone conjugates (E1-C) and estriol (E3). Estradiol was also detected but at a much lower concentration. Thus, antibodies specific for E1-C and E3 are most useful for estrogen analysis. Serum samples collected throughout 101 normal pregnancies from 45 animals were analyzed for E1-C, E3, testosterone, and cortisol. Data were log-transformed where appropriate and analyzed using a mixed model regression procedure with the random variables pregnancy ID nested within animal ID. The fixed variables included were stage of pregnancy, parity, and fetal sex. The marginal means were analyzed by gestational stage (EARLY, MID, LATE) and by month prior to parturition (MPP). For E1-C, concentrations were higher (p < 0.05) during LATE compared with EARLY and MID and were higher in nulliparous than multiparous females. For E3, concentrations were higher (p < 0.05) in EARLY than MID and LATE, but values were similar across all groups when parity was excluded from analyses. As observed for E1-C, E3 was higher in nulliparous compared to multiparous females (p < 0.05). Analysis by MMP demonstrated that E3 was elevated during months 13 to ten compared with all remaining months. Concentrations of E1-C and E3 were non-significantly higher across all MPP in nulliparous compared to multiparous animals. Testosterone concentrations increased during MID and LATE compared to EARLY (p < 0.05) and were not influenced by parity. Analysis by MPP showed significant increases in testosterone concentrations during the last eight months of gestation (p < 0.05). Nulliparous females exhibited non significantly higher concentrations than multiparous females. Cortisol concentrations were higher (p < 0.05) during LATE compared to EARLY and MID (p < 0.05), progressively increased (p < 0.05) throughout MPP but were not affected by parity. Hormone profiles across all gestational stages and MPP categories were not influenced by fetal sex. This research establishes normal reference values of serum estrogens, testosterone and cortisol during pregnancy stages in this species. Future work is needed to evaluate profiles of the aforementioned hormones in abnormal pregnancies for potential use in the clinical management of the parturient bottlenose dolphin.

Acknowledgements

The authors wish to thank the staff at the SeaWorld & Busch Gardens Reproductive Research Center and zoological/animal care laboratories at SeaWorld San Diego, San Antonio and Orlando. Interns Jenna Roseman and Gabriella Postiglione are thanked for assistance with sample collation and hormone assays.

* Presenting author

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