Marked differences in functioning of the hypothalamic-pituitary-adrenal axis between groups of men

Area of Science:

• Endocrinology
• Exercise Physiology
• Neuroendocrinology

Background:

• The hypothalamic-pituitary-adrenal (HPA) axis regulates stress response.
• Individual differences in HPA axis responsiveness exist even in healthy individuals.
• Understanding these differences is crucial for identifying susceptibility to HPA-related disorders.

Purpose of the Study:

• To compare HPA axis and growth hormone responses between high and low responders in healthy men.
• To investigate pituitary-adrenal responses to arginine vasopressin (AVP) and behavioral characteristics.
• To determine if glucocorticoid pretreatment combined with exercise can distinguish HPA responsiveness profiles.

Main Methods:

• Classified 15 healthy, moderately trained men into high (n=7) and low (n=8) responders based on ACTH response to exercise after dexamethasone (Dex).
• Evaluated HPA and growth hormone responses to exercise (90% VO2max) after placebo, Dex (4mg), or hydrocortisone (100mg).
• Assessed pituitary-adrenal responses to AVP infusion, cortisol suppression after 1mg Dex, and behavioral traits.

Main Results:

• High responders showed higher plasma ACTH responses to exercise post-placebo and Dex.
• High responders exhibited higher plasma AVP secretion during exercise, enhanced by Dex and hydrocortisone.
• Low responders demonstrated lower Dex-induced increases in basal and stimulated growth hormone secretion.
• High responders had greater ACTH responses to AVP infusion and a trend for higher trait anxiety.

Conclusions:

• Subgroups of healthy men display unique HPA axis responsiveness profiles.
• Glucocorticoid pretreatment with exercise effectively distinguishes functional HPA responsiveness between subgroups.
• This method may help identify susceptibility to disorders involving hyper- or hypo-HPA activation.