The Regulation of Adrenocorticotrophic Hormone Receptor by Corticotropin-Releasing Hormone in Human Fetal Adrenal Definitive/Transitional Zone Cells

Oct 26, 2007Reproductive sciences (Thousand Oaks, Calif.)

How corticotropin-releasing hormone controls stress hormone receptors in human fetal adrenal cells

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Abstract

CRH at 0.1 nM induces a 12-fold increase in ACTH receptor levels in fetal adrenal cells within 24 hours.

Cortisol production rises in a dose-dependent manner when exposed to CRH.
ACTHR mRNA levels increase significantly over time in response to CRH treatment.
CRH, when combined with ACTH, enhances ACTHR expression more than ACTH alone.
A binding study shows a 3.5-fold increase in ACTHR protein after 48 hours of combined CRH and ACTH treatment.
Physiologic levels of CRH may enhance fetal adrenal sensitivity to ACTH, contributing to increased cortisol production late in gestation.

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As gestation progresses, human fetal adrenals (HFA) initiate the production of cortisol, which increases placental corticotropin-releasing hormone (CRH) biosynthesis. While adrenocorticotrophic hormone (ACTH) is important for the onset of cortisol production, the late gestational surge in cortisol production occurs despite falling ACTH levels in the fetal circulation. The authors determine if CRH directly regulates the expression of the ACTH receptor (ACTHR) in HFA definitive/transitional zone (DZ/TZ) cells. DZ/TZ cells isolated from midgestation HFA were cultured before treatment with 0.01 nM to 100 nM CRH or ACTH. Cortisol was measured by radioimmunoassay. Real-time reverse-transcriptase polymerase chain reaction was used to measure ACTHR mRNA. Whole-cell ACTH binding studies were performed using I(125) (Tyr-23) ACTH. CRH produced a dose-dependent rise in cortisol production and caused a time-dependent increase in ACTHR mRNA levels between 12 and 24 hours. As little as 0.1 nM CRH induced ACTHR transcript by 12-fold at 24 hours. Together with ACTH 0.01 nM, 0.03 or 0.1 nM CRH increased ACTHR expression more than ACTH alone. Binding assays demonstrated a 3.5-fold increase in ACTHR protein at 48 hours with combined CRH and ACTH treatment. Physiologic levels of CRH seen in the late-gestation fetus stimulate DZ/TZ ACTHR expression. Since placental CRH production increases strikingly near the end of gestation, the authors suggest that CRH-induced ACTH receptor expression may increase TZ responsiveness to circulating ACTH and contribute to the late gestational rise in cortisol secretion by the HFA, participating in an endocrine cascade that is involved in fetal organ maturation and potentially in the timing of human parturition.

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The Regulation of Adrenocorticotrophic Hormone Receptor by Corticotropin-Releasing Hormone in Human Fetal Adrenal Definitive/Transitional Zone Cells

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