The Cetacean Adenohypohysis: Pathological Examination and Anatomical Description Using Immunohistochemistry
Elsa M. Haubold, MS; Daniel F. Cowan, MD
Department of Pathology, University of Texas Medical Branch, Galveston,
TX; Texas Marine Mammal Stranding Network
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.