Morphology and Histology of the Atlantic Bottlenose Dolphin (Tursiops truncatus) Adrenal Gland with Emphasis on the Medulla

This 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 beta 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.