Effects of Chronic Oestrogen Replacement on Stress‐Induced Activation of Hypothalamic‐Pituitary‐Adrenal Axis Control Pathways

Effects of Chronic Oestrogen Replacement on Stress‐Induced Activation of... Oestrogen replacement therapy reportedly suppresses hypothalamic‐pituitary‐adrenal (HPA) axis responses to an emotional stressor in postmenopausal women. However, most studies in the rat suggest a facilitatory role for oestrogen in the control of HPA axis function. One explanation for this difference may be the regimen of oestrogen replacement: during oestrogen replacement therapy, oestrogen levels are low and constant whereas most animal studies examined the HPA axis response when oestrogen levels are rising. In the present study, we assessed HPA axis stress responses in mature ovariectomized rats after plasma oestrogen levels had been maintained at physiological levels for a prolonged period (25 or 100 pg/ml for 7 days). In the case of both an emotional stressor (noise) and a physical stressor (immune challenge by systemic interleukin‐1β administration), oestrogen replacement suppressed stress‐related Fos‐like immunolabelling, in hypothalamic neuroendocrine cells and plasma adrenocorticotropin hormone responses. From the present data, and past reports, it appears unlikely that these effects of oestrogen are due to a direct action on corticotropin‐releasing factor or oxytocin cells. Therefore, to obtain some indication of oestrogen's possible site(s) of action, Fos‐like immunolabelling was mapped in the amygdala and in brainstem catecholamine groups, which are neuronal populations demonstrating substantial evidence of involvement in the generation of HPA axis stress responses. In the amygdala, oestrogen replacement suppressed central nucleus responses to immune challenge, but not to noise. Amongst catecholamine cells, oestrogen replacement was more effective against responses to noise than immune challenge, suppressing A1 and A2 (noradrenergic) and C2 (adrenergic) responses to noise, but only A1 responses to immune challenge. These data suggest that, as in postmenopausal women on oestrogen replacement therapy, chronic low‐level oestrogen replacement can suppress HPA axis stress responses in the rat. Moreover, oestrogen appears to exert effects at multiple sites within putative HPA axis control pathways, even though most of the relevant neuronal populations do not contain genomic receptors for this gonadal steroid and the pattern of oestrogen action differs for an emotional vs a physical stressor. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neuroendocrinology Wiley

Effects of Chronic Oestrogen Replacement on Stress‐Induced Activation of Hypothalamic‐Pituitary‐Adrenal Axis Control Pathways

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Publisher
Wiley
Copyright
Copyright © 2000 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0953-8194
eISSN
1365-2826
DOI
10.1046/j.1365-2826.2000.00527.x
Publisher site
See Article on Publisher Site

Abstract

Oestrogen replacement therapy reportedly suppresses hypothalamic‐pituitary‐adrenal (HPA) axis responses to an emotional stressor in postmenopausal women. However, most studies in the rat suggest a facilitatory role for oestrogen in the control of HPA axis function. One explanation for this difference may be the regimen of oestrogen replacement: during oestrogen replacement therapy, oestrogen levels are low and constant whereas most animal studies examined the HPA axis response when oestrogen levels are rising. In the present study, we assessed HPA axis stress responses in mature ovariectomized rats after plasma oestrogen levels had been maintained at physiological levels for a prolonged period (25 or 100 pg/ml for 7 days). In the case of both an emotional stressor (noise) and a physical stressor (immune challenge by systemic interleukin‐1β administration), oestrogen replacement suppressed stress‐related Fos‐like immunolabelling, in hypothalamic neuroendocrine cells and plasma adrenocorticotropin hormone responses. From the present data, and past reports, it appears unlikely that these effects of oestrogen are due to a direct action on corticotropin‐releasing factor or oxytocin cells. Therefore, to obtain some indication of oestrogen's possible site(s) of action, Fos‐like immunolabelling was mapped in the amygdala and in brainstem catecholamine groups, which are neuronal populations demonstrating substantial evidence of involvement in the generation of HPA axis stress responses. In the amygdala, oestrogen replacement suppressed central nucleus responses to immune challenge, but not to noise. Amongst catecholamine cells, oestrogen replacement was more effective against responses to noise than immune challenge, suppressing A1 and A2 (noradrenergic) and C2 (adrenergic) responses to noise, but only A1 responses to immune challenge. These data suggest that, as in postmenopausal women on oestrogen replacement therapy, chronic low‐level oestrogen replacement can suppress HPA axis stress responses in the rat. Moreover, oestrogen appears to exert effects at multiple sites within putative HPA axis control pathways, even though most of the relevant neuronal populations do not contain genomic receptors for this gonadal steroid and the pattern of oestrogen action differs for an emotional vs a physical stressor.

Journal

Journal of NeuroendocrinologyWiley

Published: Aug 19, 2000

References

  • Temporal changes of c‐ fos expression in oxytocinergic magnocellular neuroendocrine cells of the rat hypothalamus with restraint stress
    Miyata, Miyata; Itoh, Itoh; Lin, Lin; Ishiyama, Ishiyama; Nakashima, Nakashima; Kiyohara, Kiyohara
  • Neuroendocrine responses to an emotional stressor: evidence for involvement of the medial but not the central amygdala
    Dayas, Dayas; Buller, Buller; Day, Day
  • Differential localization of estrogen receptors in various vasopressin synthesizing nuclei of the rat brain
    Axelson, Axelson; Van Leeuwen, Van Leeuwen
  • Involvement of medullary catecholamine cells in neuroendocrine responses to systemic cholecystokinin
    Buller, Buller; Day, Day
  • Neuroendocrine and behavioral responses and brain pattern of c‐ fos induction associated with audiogenic stress
    Campeau, Campeau; Watson, Watson
  • The involvement of noradrenergic ascending pathways in the stress‐induced activation of ACTH and corticosterone secretions is dependent on the nature of stressors
    Gaillet, Gaillet; Lachuer, Lachuer; Malaval, Malaval; Assenmacher, Assenmacher; Szafarczyk, Szafarczyk
  • Differential recruitment of hypothalamic neuroendocrine and ventrolateral medulla catecholamine cells by non‐hypotensive and hypotensive hemorrhages
    Buller, Buller; Smith, Smith; Day, Day
  • Pathways to the secretion of adrenocorticotropin: a view from the portal
    Plotsky, Plotsky

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