To investigate the role of gonadal steroids in the hypothalamic-pituitary-adrenal (HPA) response to stress, we studied adrenocorticotrophin (ACTH) and corticosterone (B) responses to 20 min restraint stress in cycling female rats, and in ovariectomized (OVX) rats replaced with physiological levels of estradiol (E2) and progesterone (P). In cycling rats, we found significantly higher peak ACTH and B responses to stress during proestrous compared to the estrous and diestrous phases. No differences were found in either basal ACTH and B levels across the cycle phases. In a separate study, OVX rats were maintained on low, physiological levels of E2 and P with silastic implants for three days, and injected either with oil (O$ sp prime$), 10 ug of E2 (E$ sp prime$) 24 h before stress testing, or with E2 and 500 ug P 24 h and 4 h, respectively, prior to stress (EP$ sp prime$). These treatments mimicked endogenous profiles of E2 and P occurring during diestrous, proestrous, and late proestrous-early estrous phases, respectively. In response to stress, ACTH levels were higher in the E$ sp prime$ group compared to the EP$ sp prime$ and O$ sp prime$ groups. Within the 20 min stress period, ACTH levels and plasma B levels in the E$ sp prime$ group were significantly higher after the onset of stress, compared to the EP$ sp prime$ and O$ sp prime$ groups. $ beta$-endorphin-like immuno-reactive responses to restraint stress were also significantly higher in the E$ sp prime$ group. There was no effect of E2 on ACTH clearance. These results indicate that the HPA axis in the female rat is most sensitive to stress during proestrous.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.59935 |
| Date | January 1990 |
| Creators | Viau, Victor |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Psychiatry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001214153, proquestno: AAIMM67505, Theses scanned by UMI/ProQuest. |
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