Abstract 293 – Insight on the inside: histomorphological study of brown bear adrenal glands

Agnieszka Sergiel, Abbey E. Wilson, Ewa Serwa, Joanna Macur, Łukasz
Paśko, Bartosz Leszczyński, Andrzej Wróbel, Jerzy Wiater, Jumpei Tomiyasu, Heather
Bacon, Robert Maślak, Slaven Reljić, Djuro Huber

Brown bear physiology is closely tied to seasonal changes. Hypothalamic-pituitary-
adrenal (HPA) axis plays an important role in regulating physiologically distinct states
related to those, and adrenal glands are the effectors. They produce and secrete
glucocorticoid hormones (e.g., cortisol and corticosterone), which play a key role in
regulating vital physiological processes. Morphologically the adrenal glands exhibit a
high degree of variation, with significant asymmetry observed between the right and left
glands within species and interspecifically. Adrenal gland variation is also related to the
zonation of the cortex. Parameters related to its shape and size have been used as a
principal criterion for differentiating a normal gland from adrenal hyperplasia. Our
objectives were to describe histomorphology of brown bear adrenal glands, establish
reference measurements to estimate adrenal size, and to assess the effects of season,
body mass, structural body size, age, and sex of individuals on adrenal parameters. We
used 325 formalin-preserved adrenal glands collected from 173 individuals of the
Dinaric-Pindos brown bear population. The mass, length, width, thickness, and volume
of glands were measured and allometric scaling was examined. Adrenal length, width
and thickness showed negative allometry with total body length (univariate allometric
coefficients: 0.76, 0.63 and 0.8 for the right gland, and 0.64, 0.74 and 0.73 for the left
gland, respectively). On average, the mass of adrenal glands was 0.006% of the
individual body mass. Additionally, we conducted histological analysis of 21 freshly
collected adrenals of 16 individuals. Eight pairs of adrenal glands were also micro-CT-
scanned, resulting in visualizations of size, shape and surface, virtual cross-sections,
and volumetric analysis. Our study presents the first database of normal physiological,
anatomical, and histological values of adrenal glands for this species for use in health
assessments.