Advance physiology: Exercise Metabolism Part 2 Quiz part 2 (adipose tissue lipolysis)

Adipose Tissue Lipolysis: sequential hydrolysis of TG

• liberation of FFA at each step - generates:

  • diaclglycerol (DG)

  • monoacylglycerol (MG)

  • glycerol

Three things you need

• ATGL: adipose triglyceride lipase

• HSL: hormone sensitive lipase

• MGL: monoglyceride lipase

Adipose Tissue responds to dynamic exercise by

• responds to dynamic exercise by:

  • activating triacyglycerol (TG) hydrolysis

  • releasing FFA into blood

Adipose TG Lipase (ATGL)

• mediates basal and β-adrenergic TG lipolysis in adipocytes

• deletion induces obesity

• over expression produces a lean phenotype

Hormone-sensitive lipase (HSL)

• catalyzes the breakdown of diaclyglycerol (DG) to monoacylglycerol (MG) and FFA

• HSL KO mice accumulates DG

Physiologic Regulation of Resting Lipolysis

• Adipose tissue lipolysis is maintained at a low rate while the body is at rest

inhibitors of lipolysis

• insulin

  • may be the most important inhibitor at rest

  • plasma catecholamines - this is complicated

    • norepinephrine

    • epinephrine

    • at low levels they activate the a2 adrenergic receptor - inhibits lipolysis by inactivating HSL and maybe ATGL

Physiologic regulation of lipolysis during exercise

• increase in sympathetic nervous system activity, resulting in accumulation of epinephrine and norepinephrine in blood

• increase catecholamine concentrations

• release of FFA

Low levels of catecholamines stimulate _____ and ______

a2 adrenergic receptor and inhibit adipose tissue lipolysis

High levels of catecholamines stimulate ____ which stimulate _______

β-adrenergic receptors which stimulate adipose tissue lipolysis

Factors of FFa Release from adipose tissue and delivery to muscle

• plasma [FFA]

• muscle blood flow

• exercise intensity

Lipolysis and FFA release at different exercise intensities: LIGHT

• light = (≤25%Vo2max)

  • increased lipolysis and FFA delivery

Lipolysis and FFA release at different exercise intensities: MODERATE

• moderate (25-65%Vo2max)

  • increased lipolysis and FFA delivery

Lipolysis and FFA release at different exercise intensities: INTENSE

• Intense (65-85%Vo2max)

  • no change in lipolysis, decreased FFA delivery

    • due to reduced adipose tissue blood flow - and therefore reduced FFA uptake by the skeletal muscle

      • in addition to blood flow, other factors such as membrane transport of muscle metabolism also play a role in reduced FFA oxidation at higher intensities

The breakdown and release of FFA from ADIPOSE TISSUE and increased delivery of FFA to muscle are important for

increasing the use of fat as an energy source at low and moderate exercise intensities