Abstract

Prompted by the finding of apparent catecholamine-induced injury in the myocardium of stranded Cetaceans, we undertook an investigation of the adrenal glands of the Atlantic bottlenose dolphin, Tursiops truncatus, based on 41 animals examined in our laboratory. The adrenals are bilaterally symmetrical glands lying about 5-7 cm cephalad of the kidneys, near the midline. The adrenal of the bottlenose dolphin is compact, elongate and roughly triangular in cross section, with the medulla filling the central portion. Measured weights of the glands examined by us are up to 10 g for animals under 225 cm body lengths, and from 6-18 g for animals over 225 cm long. This length division roughly correlates with sexual maturity determined by examination of the gonads. The left adrenal tends to weigh about 10% more than the right. Zonation of the medulla is a g histological feature, with a consistent subcortical layer of cells about 4-6 cells thick, distinguishable from the deeper medulla on ordinary light microscopy.

Commercial monoclonal antibodies against chromogranin stain the medulla diffusely, but antibodies against dopamine b hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, and phenylethanol amine N-methyl transferase (PNMT), the enzyme that converts norepmephnne to epinephrine, demonstrate that the outer cell layer is functionally as well as morphologically distinct from the central medullary mass. Electron micrography reveals an admixture of the two organelles associated with epinephrine and nor epinephrine in the cells of the outer layer.

The significance of these findings is not clear. A similar zonal organization has been observed in all cetacean species examined in our laboratory. Studies now in progress are aimed at identifying quantifiable differences in the thickness of the medullary zones in animals of different age, physiological status, and disease state.