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Pituitary-adrenal function in the immature ovine foetus
A C McFarlane1, S Potocnik, M Towstoless
1Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
The Journal of Endocrinology
|June 1, 1995
Summary
The ovine fetus responds to stimuli by mid-gestation. Both the pituitary and adrenal glands show activity, indicating fetal readiness for stress responses.
Area of Science:
- Reproductive Endocrinology
- Fetal Physiology
- Neuroendocrinology
Background:
- The development of the pituitary-adrenal axis is crucial for fetal adaptation to stress.
- Understanding fetal endocrine responses is vital for assessing developmental maturity and potential health outcomes.
- Previous research has focused on later stages of gestation, leaving mid-gestation responses less understood.
Purpose of the Study:
- To investigate the responsiveness of the ovine fetal pituitary-adrenal axis to exogenous corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP).
- To examine the fetal pituitary-adrenal response to acute hemorrhage as an endogenous stressor.
- To determine if the ovine fetus is capable of mounting an ACTH and cortisol response by mid-gestation.
Main Methods:
- Utilized chronically cannulated ovine fetuses (74-84 days gestation) for intravenous infusions.
- Administered ovine corticotropin-releasing hormone (oCRH) and arginine vasopressin (AVP) at 1 microgram/h for 60 minutes.
- Studied acutely exteriorized fetuses (70-90 days gestation) subjected to progressive hemorrhage.
- Measured plasma ACTH and cortisol levels using radioimmunoassay.
Main Results:
- Basal ACTH levels were <20 pg/ml and cortisol levels were 6.5 +/- 1.5 nmol/l in chronically cannulated fetuses.
- Infusion of oCRH and AVP significantly increased ACTH (P < 0.05) and cortisol (P < 0.01) levels, though responses were modest.
- Hemorrhage significantly elevated ACTH levels (P < 0.05) from 117.4 +/- 32.1 pg/ml to a maximum of 329.2 +/- 112.8 pg/ml.
- The maximal ACTH response to hemorrhage correlated with a 6.6 +/- 1.2% blood volume loss.
Conclusions:
- The ovine fetal pituitary-adrenal axis is responsive to both exogenous and endogenous stimuli by mid-gestation.
- Despite low basal cortisol levels, the fetal adrenal gland can respond to elevated ACTH in the short term.
- These findings highlight the developing endocrine capacity of the fetus prior to term.