Placental Cortieotrophin-releasing Hormone Local Effects and Fetomaternal Endocrinology

Overview of Corticotrophin-Releasing Hormone (CRH)

  • CRH is produced by the human placenta in gradually increasing amounts during pregnancy, peaking at labor.

    • Involved in several pregnancy aspects: placental blood flow, prostaglandin production, and fetal development.

  • CRH potentially influences fetal organ development indirectly through fetal cortisol levels.

The Role of CRH in Pregnancy

Production and Regulation

  • Identified in the placenta by Shibasaki et al. (1982).

    • One gene for CRH located on chromosome 8 (8q13).

    • CRH mRNA and peptide in the placenta identical to hypothalamic CRH.

    • CRH detectable in maternal circulation from 16-18 weeks gestation.

  • Maternal plasma CRH levels rise exponentially with gestation, correlating with gestational length.

Fetal and Maternal Impact

  • Maternal CRH influences the maternal HPA axis.

    • Elevated CRH linked with maternal well-being during pregnancy.

  • CRH levels differ between fetal and maternal circulation, suggesting physiological roles.

  • Increased concentrations during labor indicate a role in the timing of parturition.

CRH and Fetal Development

  • CRH stimulates the fetal pituitary to produce ACTH, stimulating adrenal cortisol production.

  • Correlation found between maternal CRH and fetal cortisol, ACTH, and CRH levels.

    • Elevated fetal cortisol leads to better lung maturity.

Mechanisms Influencing CRH Production

Regulatory Factors

  • Glucocorticoids stimulate CRH expression in the placenta but inhibit it in the hypothalamus.

  • Cortisol influences CRH release in response to stress, integrating signals from maternal and fetal compartments.

    • Other hormones (e.g., estrogen, progesterone) might modify CRH gene expression indirectly.

Local Actions in the Placenta

  • CRH effects include:

    • Modulation of vascular blood flow through vasodilation mechanisms.

    • Stimulating prostaglandin production, crucial in labor onset.

Pathologies and CRH Relationship

CRH Levels in Abnormal Pregnancies

  • Elevated CRH levels observed in:

    • Pregnancy-induced hypertension.

    • Intrauterine growth retardation and fetal distress.

  • Early high CRH levels linked to risk of premature delivery.

Investigating CRH and Parturition

  • CRH levels fluctuate, indicating its role as a placental clock factor in labor.

  • A feed-forward mechanism exists where increased cortisol stimulates CRH production, suggesting regulation of pregnancy duration.

Conclusion

  • CRH acts as a crucial factor connecting maternal health, placental function, and fetal development.

    • Functions in synchronizing the timing of labor through complex hormonal interactions.

    • Indicating potential therapeutic targets for managing pregnancy-related complications.