Immunohistochemical analysis of the hypothalamic-pituitary-adrenal axis in dogs: Sex-linked and seasonal variation

This study evaluated sexual dimorphism and seasonal variations in corticotrophs and adrenal zona fasciculata in dogs, as well as the expression of oestrogen receptor alpha (ER alpha). An immunohistochemical analysis was conducted in pituitaries for ACTH and in adrenal glands for ER alpha and for the melanocortin-2-receptor (MC2R) in winter and summer. Double immunofluorescence was performed to identify ERa in corticotrophs. Females had a greater proportion of corticotrophs per field (p < 0.01), with a greater cellular area and optical density (p < 0.001) than males. Optical density of corticotrophs was greater in winter for both sexes (p < 0.001). In zona fasciculata, ERa and MC2R expression was greater in females (p < 0.001) and was greater in winter (p < 0.001). ER alpha was identified in corticotrophs. This study is the first to demonstrate ERa expression in corticotrophs and the adrenal cortex in dogs, providing evidence for sexual dimorphism and seasonal variations. (C) 2015 Elsevier Ltd. All rights reserved.