Simulated microgravity increases beta-adrenergic lipolysis in human adipose tissue

Area of Science:

• Physiology
• Endocrinology
• Metabolism

Background:

• Sympathetic nervous system activity influences adipose tissue lipolysis.
• Head-down bed rest (HDBR) is known to decrease sympathetic nervous activity.
• Understanding the impact of reduced sympathetic activity on fat metabolism is crucial.

Purpose of the Study:

• To investigate the effect of sustained sympathoinhibition via HDBR on beta-adrenergic lipolytic activity in subcutaneous adipose tissue.
• To determine if changes in beta-adrenoceptor sensitivity or postreceptor events mediate altered lipolysis.

Main Methods:

• Utilized 5-day head-down bed rest (HDBR) in eight healthy men.
• Employed microdialysis for in situ assessment of beta-adrenoceptor (AR) sensitivity in adipose tissue.
• Performed in vitro studies on isolated adipocytes to evaluate adrenergic sensitivity and lipolytic responses.

Main Results:

• HDBR increased beta-AR sensitivity to lipolysis and vascular tone.
• Basal and stimulated lipolysis in isolated adipocytes were enhanced post-HDBR.
• When normalized for postreceptor events, lipolytic responses to beta-AR agonists remained unchanged, suggesting postreceptor mediation.

Conclusions:

• Sustained sympathoinhibition through HDBR enhances the lipolytic beta-adrenergic response in adipose tissue.
• This hypersensitization appears to be primarily due to increased postreceptor signaling within adipocytes.
• No significant changes were observed in lymphocyte beta-AR number or alpha 2-AR-mediated effects.