Evidence for cortisol–cortisone metabolism by marine mammal blubber
Blubber, a specialized hyperdermic adipose tissue found in marine mammals, has been identified as a useful tissue for the assessment of steroid hormone homeostasis in cetaceans. However, blubber cortisol measurements are not quantitatively predictive of circulating cortisol concentrations in bottlenose dolphins. In other mammals, adipose tissue metabolizes steroid hormones. Thus, it is proposed that the disagreement between blubber and blood cortisol in bottlenose dolphins could be due in part to metabolism of corticosteroids in blubber. The purpose of this study is to characterize the ability of blubber to interconvert cortisol and cortisone using an in vitro design. Results demonstrate that bottlenose dolphin blubber microsomes interconvert cortisol and cortisone, an effect that is abated by denaturing the microsomes, indicating this is an enzymatic process. These findings lead to the conclusion that blubber is likely a site of active steroid metabolism, which should be considered in future studies utilizing blubber as a matrix for endocrine assessment.
This research was made possible through a grant from The Gulf of Mexico Research Initiative and funding provided by the National Institute of Standards and Technology. Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org ( https://doi.org/10.7266/n74b2zsr). We would like to thank Michael Janech, the Medical University of South Carolina (MUSC) Nephrology Proteomics Laboratory, and Sang-Ho Kwon for assistance in experimental design and/or the use of laboratory space and equipment for microsome isolations. We thank the South Carolina Marine Mammal Stranding Network for their efforts in sample collection. Finally, we thank the reviewers for their time and effort dedicated to reviewing this manuscript.
Compliance with ethical standards
Samples were collected under NOAA’s authority to collect samples under Section 109(h) of the MMPA. All applicable international, national, and institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted. Commercial equipment, instruments, or materials are identified to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology nor the National Oceanographic and Atmospheric Administration, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
Conflict of interest
The authors declare that they have no conflict of interest in the publication of this manuscript.
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