Scattered reports dating from the late 1800's describe the anatomy of the pituitary of some cetacean species. However, the observations have generally been based on a limited number of animals. Since 1991, in a cooperative effort with the Texas Marine Mammal Stranding Network we have collected intact pituitaries from 43 freshly stranded cetaceans, the majority from bottlenose dolphins but also from a rough toothed dolphin, a spotted dolphin, a striped dolphin, a pilot whale, a sperm whale, a pygmy sperm whale, and a beaked whale. Pituitary and brain weights were obtained from 35 of the animals with the bottlenose dolphin pituitary weights ranging from 0.72 - 2.60 gm.

Gross and histological examination revealed hyperplastic nodules, small colloid cysts, and focal calcifications in 8 of the pituitaries which, at 19% of the examined population, is a relatively high incidence. An earlier report from this laboratory suggested that commercially available labeled anti-human hormone antibodies will react with dolphin tissues (Kumar and Cowan 1994). Using these antibodies, cetacean pituitary hormones were identified for the first time as far as we know, using immunocytochemistry techniques. Mouse anti-human antibodies against prolactin, adrenocorticotropic hormone (ACTH), growth hormone (GH) and luteinizing hormone (LH) were used to identify distributions within the dolphin adenohypophysis, and correlated with cell distribution using conventional stains (hematoxylin and eosin, and PAS/Orange G).

Although some species were represented by only one individual, apparent species differences in cell pattern can be recognized. In all species, ACTH and GH were abundant and distributed throughout the adenohypophysis. ACTH reactive cells were frequently clustered and regularly arranged around sinusoids, and in the bottlenose dolphin, most heavily concentrated at the base of the gland. Prolactin and LH reactive cells were usually sparse and occurred as single cells, sometimes most heavily concentrated near the fibrous septal membrane separating the adenohypophysis from the neurohypophysis. Prolactin reactivity was generally located only in the periphery of the adenohypophysis. A lactating striped dolphin had abundant prolactin and LH reacting cells. The pilot whale pituitary had many colloid-filled micro follicles, imparting a thyroid-like histological appearance. ACTH staining cells were less abundant when compared to other cetacean species.

Except for the bottlenose dolphin, small samples preclude interpretation of the number and distribution of hormone secreting cells of the cetacean adenohypophysis at differing ages and physiological states. The strong reactivity of anti-human hormone antibodies in all species studied, however, provides evidence for evolutionary conservation of the cetacean pituitary hormones. These reagents may prove useful in our further studies of stranded cetaceans.

Reference

1.  Kumar, D, and Cowan, DF: Cross-reactivity of antibodies to human antigens with tissues of the bottlenose dolphin, Tursiops truncatus using immunoperoxidase techniques. Marine Mammal Science 10:188-194, 1994.