L3.1 Lipid Metabolism

Question 1

How are fats broken down?

Answer 1

• Fats can only be oxidised aerobically
• Lipoprotein lipase → breaks down circulating trigly (<10% during exercise)

Question 2

Relationship of exercise (not intensity) and durationon fat oxidation?

Answer 2

• After exercise → muscles able to clear trigly more (↑oxidation)
• ↑duration → ↑lipolysis > ↑FA uptake > FA oxidation

Question 3

What is the relationship between usage of FA from adipose tissues and muscles?

Answer 3

• Reciprocal relationship between FA from adipose & FA from muscles
• ↑use of FA from adipose → ↓ use of FA from muscles

Question 4

What are the 3 triglyceride lipases?

Answer 4

• 1) Adipose tissue triglyceride lipase (ATGL) – trigly to bigly
• 2) Hormone sensitive lipase (HSL) – bigly to monogly
• 3) Monoglyceride lipase (MGL) – monogly to gly & FA
  
  • ATGL and HSL can be phosphorylated ∴ are the regulatory steps

Question 5

How is adipose tissue lipolysis regulated?

Answer 5

• ATGL & HSL
• Β-adrenergic stimulation (↑Adrenaline → ↑HSL → ↑lipolysis)
• ↓ Insulin (during exercise)
• Adipose tissue blood flow (↓during exercise - ↓release of FA into bloodstream)
• FFA/Albumin ratio (albumin binds FA → transports hydrophobic FFA through hydrophilic membrane)
• Caffeine → ↑FA (Spares glycolysis)

Question 6

How is muscle lipolysis regulated?

Answer 6

• ATGL & HSL(main)
• Β-adrenergic stimulation
• ERK (kinase responds to Ca2+) → simulates mobilisation of fats
• AMPK inhibits HSL activation (still ?)
• ↑Blood glucose → ↑oxidation of triglyceride
• Plasma FFA availability (↑availability → ↑lipolysis)

Question 7

What are the determinants of muscle FA uptake?

Answer 7

• FA transporters
• [FA] (for conc gradient)
• Ability of muscles to oxidise FA
• Carnitine (helps FA across membrane) & CPT (combines carnitine & FA)
• Β-oxidative capacity in mito (HAD enz involved in 1st step oxidation of FA)

Question 8

What are the methods of muscle FA uptake by transporters?

Answer 8

1) Simple diffusion
2) CD36 & FABP → enhances diffusion gradient, facilitates FA uptake
3) Long chain FA uptake via FATP

Question 9

What is the effect of carnitine during exercise?

Answer 9

• ↑Acetylcarnitine, ↓carnitine (at high intensities)
  
  • Carnitine combines with acetyl-CoA to form acetylcarnitine
    
    • Prevents overwhelming the TCA cycle from high levels of glycolysis during high intensities
• *↑carnitine → ↑FA uptake → ↑ Fat burn
• ↑HAD in muscles → burn more fats, ↑fat oxidation
  
  • ∴↓FA going into adipose tissue

Question 10

Why does an increase in exercise intensity rely less on fats and more on CHO oxidation?

Answer 10

• ↑intensity → ↓fat, ↑CHO utilisation
• At high intensities → ↓FFA availability, ↑glycolytic flux which inhibits CPT activity and mitochondrial FA uptake
  
  • Due to ↓Carnitine availability
• CHO oxidation → ↑power & require less O2 for ATP prod
• Med Chain FA oxidation does not change at high intensity (not limited by mitochondrial transport system)

Question 11

What is the effect of training on lipid metabolism?

Answer 11

• ↑FA uptake & Fat oxidation (greater) – uses more muscle triglyceride
• Uses both blood & Muscle FA
• ↑Muscle CPT levels
• ↑FA transport