Introduccin
The morphological and functional sexual dimorphism of the hypothalamic-pituitary-adrenal axis (HPA) has been described in various species. There are also some reports about the seasonal variations of this axis. However there are no studies about sexual dimorphism and seasonal variations of this axis...
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
| Publicado: |
Universidad de Buenos Aires. Facultad de Ciencias Veterinarias
2015
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=avaposgra&cl=CL1&d=HWA_1342 https://repositoriouba.sisbi.uba.ar/gsdl/collect/avaposgra/index/assoc/HWA_1342.dir/1342.PDF |
| Aporte de: |
| Sumario: | The morphological and functional sexual dimorphism of the hypothalamic-pituitary-adrenal axis (HPA) has been described in various species. There are also some reports about the seasonal variations of this axis. However there are no studies about sexual dimorphism and seasonal variations of this axis in the dog. Thus the objective of this study was to determine whether there are variations in the dog´s HPA hormones (adrenocorticotrophin [ACTH], alfa-melanocyte-stimulating hormone [?-MSH] and cortisol) according to the sex, gonadal status (neutered or not) and photoperiod (positive or negative) in basal condition (like anoestrus) and along the oestrous cycle.\nFurthermore, this study evaluated if the dog shows morphological sexual dimorphism of the corticotroph area of the pituitary gland and zona fasciculata of the adrenal gland; and determined whether these tissues show seasonal variations. The expression of oestrogen receptor alpha (ER?) in the corticotroph cells and zona fasciculata was also evaluated, as well as the progesterone receptor (PR) in the fasciculate zone.\nIn the hormonal assay, the population under study consisted in intact females (n=11), intact males (n=6), neutered males (n=5) and neutered females (n=6).\nThe morphological study was performed by means of an immunohistochemical analysis of pituitary and adrenal glands obtained in negative photoperiod (females [n = 7] and males [n = 7]) and positive photoperiod (females [n = 7] and males [n = 7]) for ACTH in the pituitary gland and for ER?, PR and for the ACTH receptor (melanocortin-2-receptor, MC2R) in the adrenal gland. Double immunofluorescence was performed to identify ER? in corticotrophs. The pituitary gland analysis included the proportion of corticotrophs per field, corticotroph cellular, nuclear, and cytoplasmic area, and their optical density. The RE? and PR expression was evaluated by the proportion of positive cells per field, and MC2R expression was evaluated through the optical density. In basal condition (intact males, neutered males, neutered females and intact females in anestrus) ACTH, ?-MSH and cortisol were not affected by the sex or the gonadal status. By contrast, cortisol showed greater values in negative photoperiod than in positive in all the studied groups (P<0.05) except for the intact females in anestrus. Along the oestrous cycle, all the studied hormones showed variations (P<0.0001). The greatest concentrations of ACTH were observed at proestrus, while ?-MSH and cortisol showed their greatest concentrations at oestrus. The three hormones decreased in diestrus. ACTH and cortisol concentrations were higher at negative photoperiod (P=0.04 and P<0.0001, respectively), while ?-MSH concentrations were higher at positive photoperiod (P=0.012), In the group of females oestradiol and progesterone correlated with ACTH (r=0.75, P<0.0001; r=0.34, P<0.01, respectively), ?-MSH (r=0.49, P<0.0001; r=0.52, P<0.0001, respectively) and cortisol (r=0.33, P<0.01; r=0.5, P<0.0001, respectively). The morphological study revealed that females had a greater proportion of corticotroph cells/total cells per field (p < 0.01). Both cellular and cytoplasmic areas of these cells were greater in females than in males in both photoperiods (p < 0.001). No significant differences were found for these parameters between photoperiods in either sex. Optical density of corticotrophs was greater in females than males in both photoperiods (p < 0.001) and greater in negative photoperiod than in positive photoperiod for both sexes (p < 0.001). ER? was identified in the adrenal zona fasciculata and expressed at higher levels in females than in males (p < 0.001). The optical density of MC2R immunostaining was greater in females than in males (p < 0.001). Immunostaining for PR was not found. The expression of both receptors was greater in negative photoperiod in both males and ?Estudio del ára corticotropa del perro en relación al sexo y variaciones estacionales? Página 12\nfemales (p < 0.001). ER? was identified in some corticotrophs; however, a quantitative analysis was not conducted because of low expression. These results provide evidence that the dog shows both morphological and functional sexual dimorphism of the HPA axis. Furthermore, these findings are the first to demonstrate ER? expression in corticotrophs and the adrenal cortex in this species, suggesting a site for oestradiol action. Binding to its receptor, oestradiol could exert a regulatory action on the HPA axis. There are also hormonal and morphological differences between photoperiods, which could be related to climatic or metabolic adaptations that remain to be studied. |
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