Estrogens decrease expression of the corticotropin-releasing factor gene in the hypothalamic paraventricular nucleus and of the proopiomelanocortin gene in the anterior pituitary of ovariectomized rats

Abstract

It is known that estrogens modulate the hypothalamopituitary—adrenal (HPA) axis both under resting conditions and during exposure to stress. Nevertheless, the site of action of estrogens is not still fully elucidated. We sought to determine if estrogens could act on the major hypothalamic ACTH secretagogue: corticotropin-releasing factor (CRF). Mature rats were ovariectomized (OVX) and 2 weeks later implanted with silastic capsules containing 17β-estradiol (E₂). Animals were sacrificed 7 days later. CRF mRNA in the hypothalamic paraventricular nucleus (PVN) and proopiomelanocortin (POMC) mRNA in the anterior pituitary were measured byin situ hybridization. CRF content in the median eminence was measured by semiquantitative immunocytochemistry. E₂ treatment induced a significant decrease of CRF mRNA levels in the PVN (3.70±0.14vs 4.79±0.15 copies of probe×10⁻³/μm³ of tissue in OVX rats,P<0.05), an accumulation of immunoreactive CRF in the zona externa of the median eminence (207±36vs 100±15% in OVX rats,P<0.05), and a decrease of POMC mRNA levels in the anterior pituitary (4.6±0.6vs 6.9±0.6 copies of probe ×10⁻²/μm³ of tissue in OVX rats,P<0.05). These results demonstrate that estrogens have a negative effect on CRF gene expression and secretion and on POMC gene expression. Whether estrogens modulate directly the CRF-synthesizing cells or act through an increase of the glucocorticoid negative feedback remains to be determined.