biological effects of gh
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Biological effects of GH. Somatotropic Growth and cell proliferation IGF-I mediated Metabolic Direct action of GH IGF-I independent Many tissues All nutrients. Effects of GH on metabolism Nutrient partitioning After absorption Independent of digestion process - PowerPoint PPT PresentationTRANSCRIPT
Biological effects of GH
• Somatotropic– Growth and cell proliferation
• IGF-I mediated
• Metabolic– Direct action of GH
• IGF-I independent• Many tissues• All nutrients
• Effects of GH on metabolism– Nutrient partitioning
• After absorption– Independent of digestion process– Independent of nutrient expenditure
Nutrient partitioning during growth
• Alteration of growth by exogenous GH– Alteration in nutrient partitioning between
muscles and adipose tissue• Increased daily gain• Increased feed efficiency• Decreased fat deposition• Increased protein deposition
– Age-dependent response
• Action of GH– Different between adipose and muscle– Growth of muscle in response to GH
• Depends on availability of dietary proteins and energy
• Involves IGF-I
– Decreased fat accumulation• Inhibition of glucose uptake
• Action of GH– Decreased fat accumulation
• Inhibition of glucose utilization• Glucose diverted to muscles • Net results
– Decreased adipocyte hypertrophy– Increased muscle growth
Effects on adipoccytes
• Chronic
• Lipogenesis– Inhibited
• Fatty acid synthesis
• Lipolysis– Stimulated when undernutrition
• Mechanism– Inhibition of insulin action on adipocytes
• Decreased sensitivity of adipocytes to insulin stimulation
– Decreased glucose usage by the cells– Independent of receptor number or intracellular
signaling system
• Inhibition of fatty acid synthase expression– Interference with insulin signaling pathway– Direct genomic effects
• Effects on lipolysis– Indirect mechanism
• Alteration of adipocyte responsiveness to acute lipolytic signaling pathway
• Highly dependent on nutritional status of the individual
• Increased hepatic gluconeogenesis– Direct effects– Inhibition of insulin action
• Increased efficiency of amino acid utilization– Reduced oxidation– Results in muscle fiber hypertrophy
Pancreatic hormones
Pancreas
• Exocrine organ– Digestive enzymes
• Discovery of the first hormone (secretin)
• Endocrine organ– Islets
• Described by Langerhans
– Islet of Langerhans
• Cell composition– Two major types
• Alpha– Glucagon
• Beta– Insulin
– Other cells• D cells (SS)• F cells (pancreatic
polypeptide)
Regulation of glucose metabolism
• Glucose homeostasis– Movement of glucose into and out of
extracellular space• Involvement of many tissues
– Liver– Adipose tissue– Muscle
• Two hormones– Insulin– Glucagon
Regulation of glucose metabolism
• Glucose homeostasis– Basic concept
• Coordinated relationship between alpha (glucagon) and beta (insulin) cells under control of glucose sensor
Regulation of glucose metabolism
• Glucose homeostasis– Basic concept
• Particular arrangement of cells within the islet
• Specialized cell membrane
Insulin
• Required for normal growth and development
• Only hormone that can lower blood glucose level– Dominant metabolic regulator
• Unregulated glucose level if absent• Hypoglycemia if too high
– Cause neural shock
• Biochemistry– Two subunits
• Alpha and beta• Linked by two disulfide
bridges
– Synthesized as prohormone
• Preproinsulin– Proinsulin precursor
• Proteolytic cleavage– Proinsulin– Formation of disulfide
bridges
• Insulin– Coupled with zinc within the beta cells– Very short life
• Around 5 to 15 min after synthesis• Metabolized by kidneys and liver
Glucagon
• Biochemistry– Single peptide
• 29 AA• Similar structurally to
gastric inhibitory peptide and VIP
• Cleaved from larger protein
• Highly conserved– Identical among
mammals
Other pancreatic peptides
• SS– Localized in D cells
• Located adjacent to alpha and beta cells– Local action of SS
– Affects function of intestine• Movement of nutrients
• Pancreatic polypeptide– Unclear function in mammals
• Suppression of SS secretion by pancreas and intestine
• Inhibition of gallbladder and pancreatic enzyme secretion
– Secretion affected by nutrient uptake by the intestine