Cortisol feedback in adrenalectomized adult sheep

Area of Science:

• Endocrinology
• Neuroendocrinology
• Physiology

Background:

• The hypothalamic-pituitary-adrenal (HPA) axis regulates the body's response to stress.
• Cortisol, a key glucocorticoid, exerts negative feedback on the HPA axis.
• Understanding the precise sites and sensitivities of cortisol feedback is crucial for HPA axis regulation.

Purpose of the Study:

• To investigate the sensitivity of cortisol feedback on adrenocorticotropic hormone (ACTH) secretion in adult sheep.
• To determine the role of the pituitary gland as a site for glucocorticoid feedback.
• To examine the influence of cortisol levels on the ACTH response to corticotropin-releasing factor (CRF) and arginine vasopressin (AVP).

Main Methods:

• Adrenalectomized (ADX) adult sheep received low or high intravenous cortisol replacement.
• Dose-response studies were conducted using exogenous corticotropin-releasing factor (CRF) and arginine vasopressin (AVP).
• ACTH and AVP release were measured under varying cortisol concentrations and stress conditions (hemorrhage).

Main Results:

• High cortisol levels inhibited ACTH secretion in response to CRF and AVP individually.
• Combined CRF and AVP administration stimulated ACTH release even under high cortisol conditions.
• Glucocorticoid inhibition of ACTH release during hemorrhage was more pronounced than inhibition of AVP release.

Conclusions:

• The pituitary gland is a major site of cortisol's negative feedback on ACTH secretion in sheep.
• Physiological increases in cortisol can suppress ACTH response to CRF and AVP.
• The ACTH response system is more sensitive to glucocorticoid negative feedback than the AVP release system during stress.