Attenuation of hypothalamic-pituitary-adrenal axis stress responses in late pregnancy: changes in feedforward and feedback mechanisms.
The hypothalamic-pituitary-adrenal axis is hyporesponsive to stress in late pregnancy, exemplified as reduced adrenocorticotropic hormone (ACTH) and corticosterone responses to restraint, but the mechanisms are unknown. We investigated forward drive and negative feedback upon the hypothalamic-pituitary-adrenal axis in pregnant rats. Corticotropin-releasing hormone (CRH) and vasopressin mRNA expression in the parvocellular paraventricular nucleus and mineralocorticoid and glucocorticoid receptor expression in the paraventricular nucleus and hippocampus were quantified with in situ hybridization. Because it can enhance the corticosterone negative feedback signal, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) bioactivity in these brain regions and anterior pituitary was measured in vitro, and ACTH and corticosterone stress responses were measured after intracerebroventricular glycyrrhetinic acid, an 11beta-HSD inhibitor. Changes in corticosterone feedback on ACTH secretion were examined after pharmacological adrenalectomy by metyrapone and aminoglutethimide. Parvocellular paraventricular nucleus CRH mRNA content was reduced on day 21 and the CRH mRNA : vasopressin mRNA ratio was unaltered, indicating decreased production of both CRH and vasopressin. An increase in glucocorticoid receptor mRNA expression in the dentate gyrus (mineralocorticoid receptor mRNA expression was unaltered) and increased 11beta-HSD1 activity in the paraventricular nucleus and anterior pituitary suggest an increase in slow negative feedback mechanisms in pregnancy, but glycyrrhetinic acid did not modify the stress response. After metyrapone/aminoglutethimide treatment, corticosterone decreased ACTH secretion more slowly in pregnancy, indicating a decrease in rapid feedback sensitivity. Thus, reduced forward drive rather than increased effectiveness of glucocorticoid negative feedback may underlie stress hyporesponsiveness of the hypothalamic-pituitary-adrenal axis in pregnancy.
Johnstone
H A
HA
Departments of Biomedical Sciences and Molecular Endocrinology, University of Edinburgh, Edinburgh, UK. Max Planck Institute of Psychiatry, Munich, Germany.
Wigger
A
A
Douglas
A J
AJ
Neumann
I D
ID
Landgraf
R
R
Seckl
J R
JR
Russell
J A
JA
D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1; D000315:Adrenalectomy / Q000379:methods; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000616:Aminoglutethimide; D000704:Analysis of Variance; D000818:Animals; D019540:Area Under Curve; D003345:Corticosterone / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D005246:Feedback / Q000502:physiology*; D005260:Female; D006034:Glycyrrhetinic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000378:metabolism; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000378:metabolism*; D008797:Metyrapone; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012149:Restraint, Physical; D013312:Stress, Physiological / Q000378:metabolism*; D014667:Vasopressins / Q000235:genetics / Q000378:metabolism
D012333:RNA, Messenger; D000616:Aminoglutethimide; D014667:Vasopressins; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D006913:Hydroxysteroid Dehydrogenases; D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1; D006034:Glycyrrhetinic Acid; D003345:Corticosterone; D008797:Metyrapone