Do leptin and insulin signal adiposity?

Area of Science:

• Physiology
• Neuroendocrinology
• Energy Homeostasis

Background:

• Adiposity regulation relies on endocrine signals informing the brain about adipose tissue (AT) mass.
• Insulin and leptin are established adiposity signals, with amylin, ghrelin, and peptide YY also hypothesized.
• Evidence supporting these signals includes hormone-adiposity correlations, receptor presence, and effects of mutations.

Purpose of the Study:

• To evaluate if circulating insulin and leptin levels encode necessary information to function as adiposity signals.
• To distinguish between regulation of AT mass in steady versus dynamic states.
• To assess the strength of evidence supporting insulin and leptin as adiposity signals.

Main Methods:

• Focus on evidence from associations between basal hormone levels and adiposity levels.
• Emphasis on the distinction between steady and dynamic states of AT mass regulation.
• Analysis of experimental designs, particularly those involving perturbations causing changes in adiposity.

Main Results:

• Limited studies exist that investigate adiposity signals during dynamic changes in AT mass.
• Available evidence does not strongly support the hypothesis that insulin and leptin function as adiposity signals.
• The focus on steady-state associations may not fully capture the regulatory role of adiposity signals.

Conclusions:

• The question of how adiposity is signaled to the brain remains largely unresolved.
• Current evidence is insufficient to confirm the role of insulin and leptin as effective adiposity signals.
• Further research using dynamic state experimental designs is needed to elucidate adiposity signaling pathways.