Insulin and Glucagon

Four Major Tissues in Fuel Metabolism

• Liver

• Adipose TIssue

• Muscle

• Brain

Communication Tissues is mediated by:

• Nervous system

• Availability of substrates

• Variation of plasma hormone levels

Integration of metabolism is controlled primarily by 2 peptide hormones

Insulin and Glucagon

Insulin

Peptide hormone produced by BETA cells

Most IMPORTANT hormone containing use of fuels

ANABOLIC metabolic effects = glycogen TAGs proteins

2 polypeptide chains if composed of 51 AA link by short half bridges

Has short half life

Regulation of insulin

In testimony of carb rich meal —> Rise of glucose —> Primary stimulus of insulin secretion

Ingestion of Fatty acids and amino acids enhance glucose stimulated secretion of insulin

Ingestion of food —> Release of INCRETIN hormones from small intestine = increase sensitivity of beta cells to glucose

INCRETINS

• Glucagon-like protein-1 (GLP-1)

• Glucose-dependent insulinotropic peptide OR gastric-inhibitory polypeptide (GIP)

Decrease of Synthesis and Release of INSULIN

Scarce dietary fuels and during periods of STRESS (Infection, hypoxia, and vigorous excercise)

Catecholamine Hormones

Norepinephrine and Epinephrine

• mediates the synthesis and release of dietary fuels

Cause RAPID MOBILIZATION

• Glycogen Breakdown/Proudction

• Lipolysis

Glycogen Breakdown

Type of rapid mobilization

Glucose from liver break down glycogen

Lipolysis

Type of rapid mobilization

• Fatty acids from adipose tissue via LIPOLYSIS

METABOLIC EFFECTS OF INSULIN

• PROMOTES the STORAGE of nutrients as Glycogen TAG and Protein and inhibits mobilization

• Muscle and Adipose increase

• Decrease in glycogenogenesis and Glyconeogenesis

Carb Metabolism in Insulin

• Promote storage in liver muscle and adipose tissue

• In Liver and Muscle —> Stored as Glycogen via Glycogen synthesis (Glycogenesis)

Lipid Metabolism Effects in Insulin

• Reduction in fatty acid RELEASE by inhibiting LIPASE

• Increases transport and metabolism of glucose into ADIPOCYTES → FAs added to glycerol → Increase in TAG

Protein Metabolism Effects in Insulin

Stimulated entry of AAs into cells and increase protein synthesis

Glucagon

Peptide Hormone secreted by ALPHA cells of islets of Langerhans of endocrine pancrease

Acts to maintain blood glucose levels through glycogenolysis and gluconeogenesis

Short half life

COUNTERREGULATORY HORMONES

Oppose many actions of insulin consists of:

• Glucagon

• Epinephrine

• Norepinephrine

• Cortisol

• Growth Hormone

Glucagon Regulation: Increase

• increased by Hypoglycemia, AAs, and catecholamines

• Primary stimulus

• Some amino acids (e.g. Arginine)

• Adrenal Medulla = catecholamines

Glucagon Regulation: Decrease

Elevated blood glucose and insulin

Glucagon Metabolic effects

Glucagon is a Catabolic hormone

• binds to G-protein coupled receptor —> Activation of adenylyl cyclase —> increase in cAMP —> Activates PKA

Carbohydrate mechanism in Glucagon

Immediate rise in blood glucose

Increase in breakdown of liver glycogen and increase in hepatic gluconeogenesis

Lipid Metabolism in Glucagon

Inhibition of fatty acid SYNTHESIS and increase in fatty acid OXIDATION

The MAJOR activators of lipase are the CATECHOLAMINES

Free FAs released are taken up by the liver → Oxidized to acetyl-CoA → Used in KETONE synthesis

Protein Metabolism in Glucagon

Increases uptake by the liver of AAs supplied by muscle → Increase in availability of carbon skeletons for gluconeogenesis

Plasma levels of AAs are decreased