Local factors modulate tissue-specific NEFA utilization: assessment in rats using 3H-(R)-2-bromopalmitate

Area of Science:

• Metabolic Physiology
• Biochemistry
• Endocrinology

Background:

• Insulin resistance is linked to increased muscle lipid content, suggesting impaired lipid metabolism.
• Understanding tissue-specific fatty acid uptake is crucial for metabolic research.

Purpose of the Study:

• To quantify individual tissue nonesterified fatty acid (NEFA) uptake in rats under various metabolic conditions.
• To investigate the influence of fasting, beta-oxidation blockade, and insulin on NEFA uptake and clearance.

Main Methods:

• Utilized a novel fatty-acid tracer, [9,10-3H]-(R)-2-bromopalmitate (3H-R-BrP), in conscious male Wistar rats.
• Administered tracer during fasting (5, 18, 36 h), etomoxir-induced beta-oxidation blockade, and insulin infusion.
• Calculated NEFA clearance (K(f)*) and uptake (R(f)*) rates based on tissue tracer accumulation.

Main Results:

• Basal NEFA uptake correlated with tissue oxidative capacity (BAT > HRT > DPHM > RQ > WQ > WAT).
• Fasting increased NEFA clearance in white adipose tissue (WAT) but elevated plasma NEFA levels, tending to increase uptake in most tissues.
• Etomoxir reduced clearance in oxidative tissues; insulin decreased uptake in most tissues but increased it in WAT, BAT, and WQ.

Conclusions:

• This is the first study to measure tissue-specific NEFA uptake in conscious rats across different metabolic states.
• Tissue NEFA utilization is regulated by systemic availability and local factors, including early uptake and metabolic sequestration influenced by oxidation.