SummaryThis study provides the first detailed description of the Atlantic bottlenose dolphin (Tursiops truncatus) adrenal gland with emphasis on the medulla. Thirty-one dolphins of varying age and sex were used in this study. No statistical differences were found between the right and left gland mass, however, the left was typically greater. Mean mass for the right and left adrenal glands were 4.99 ± 0.513 and 5.36 ± 0.558 g, respectively. No statistical differences were found between average gland mass and sexual maturity or sex. The average cortex/medulla ratio was 1.22 ± 0.060 meaning approximately 48% is cortex, 41% is medulla, and 11% was categorized as other (i.e. blood vessels, connective tissue, etc.). The cortex contained pseudolobules and the typical zonation. A medullary band, consisting of highly basophilic staining cells was found at the periphery of the medulla. Projections of the medulla to the gland capsule were noted. Immunolabelling with polyclonal antibodies against the enzymes dopamine b hydroxylase and phenylethanolamine N-methyl transferase indicated that noradrenaline producing cells are found throughout the medulla including the medullary band while adrenaline producing cells are only found within the medullary band. Transmission electron microscopy confirmed the presence of two distinct cell populations within the medullary band and a single cell population throughout the medulla.

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Systematic necropsies were performed on 63 bottlenose dolphins (Tursiops truncatus), and data on organ mass, standard body length (SBL), body mass (BM), gender, sexual maturity, and age were measured and/or estimated. Animals were extremely fresh and recovered from along the Texas and Louisiana coastline in the northwestern Gulf of Mexico. Organ reference tables were established for this species to facilitate comparisons with other bottlenose dolphins and to provide a baseline for other cetacean species. Organs examined included lungs, adrenal glands, kidneys, testes, ovaries, heart, liver, pancreas, brain, pituitary, thyroid, thymus, and spleen. Individuals were separated into three size classes: < 175 cm, 175-225 cm, and > 225 cm, based on SBL to further facilitate comparisons. Growth rates of length and mass were described using Gompertz nonlinear models as a function of gender. No sexual dimorphism was identified in BM or organ weights, and SBL was only significantly larger for older mature males. SBL and BM were strongly correlated with age when all animals were included in analyses, although this is not an accurate predictor of age, especially in older individuals. Organ weights were significantly correlated with both SBL (except thymus and spleen) and BM (except left ovary, spleen, and thymus). Age was significantly correlated with all organ weights (except thymus, thyroid, and ovaries). There were no significant differences in the weight of any paired organs (adrenal glands, kidneys, lungs, ovaries, testes), and all were significantly correlated with BM. These data on organ weights of bottlenose dolphins, when interpreted with SBL, BM, and age, are significant tools for pathologists and veterinarians interpreting animal health status.