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Related Experiment Videos

Does a decrease in cortisol negative feedback efficacy precede ovine parturition?

C E Wood

    The American Journal of Physiology
    |March 1, 1987
    PubMed
    Summary
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    Parturition in sheep involves increased fetal cortisol, but the mechanism remains unclear. This study shows that late-gestation fetal sheep exhibit reduced negative feedback sensitivity to cortisol, allowing for increased adrenocorticotropin hormone (ACTH) secretion.

    Area of Science:

    • Reproductive Endocrinology
    • Fetal Physiology
    • Animal Science

    Background:

    • Parturition in ruminants is initiated by increased fetal cortisol secretion.
    • The precise mechanism driving elevated fetal adrenal activity is not fully understood.
    • A potential mechanism involves reduced fetal hypothalamopituitary sensitivity to cortisol's negative feedback.

    Purpose of the Study:

    • To investigate the sensitivity of the fetal hypothalamopituitary axis to cortisol negative feedback in late-gestation sheep.
    • To determine if reduced cortisol negative feedback is associated with increased fetal adrenocorticotropin hormone (ACTH) levels.

    Main Methods:

    • Seven fetal sheep (129-142 days gestation) were surgically prepared with vascular catheters.
    • Fetal sheep received intravenous infusions of either cortisol (10 µg/min) or vehicle for 5 hours.

    Related Experiment Videos

  • Adrenocorticotropin hormone (ACTH) response to sodium nitroprusside was assessed after cortisol or vehicle infusion.

    • Main Results:

    • Cortisol infusion significantly elevated fetal plasma cortisol levels.
    • In late-gestation fetuses, ACTH response to sodium nitroprusside was observed even after elevated cortisol levels.
    • This contrasts with younger fetuses where similar cortisol increases completely blocked ACTH response.

    Conclusions:

    • The preparturient surge in fetal ACTH in sheep is associated with a diminished negative feedback effect of cortisol.
    • Fetal hypothalamopituitary axis demonstrates decreased sensitivity to cortisol negative feedback near term.
    • This decreased sensitivity is a key factor in the cortisol-stimulated parturition process in ruminants.