III.3.B.f. Glucagon

Glucagon is produced from proglucagon (158 amino acids), which is converted to various hormones, such as glucagon, glicentin-related polypeptide (GLRP), GLRP-1, GLRP-2 and glicentin.

It is released from pancreatic A cells and gastrointestinal cells.

Glucagon secretion is increased by

• a decreased blood Glu level (hypoglycemia),
• the presence of glucocorticoids,
  • permissive effects: glucocorticoid hormones are needed for glucagon to exert its various effects,
• increased levels of various amino acids in the blood (Arg, Leu and Lys):
  • the same amino acids stimulate the release of glucagon and insulin,  the relevance of this to synchronize hormone release.
• a lack of insulin:
  • insulin inhibits expression of the glucagon gene,
• catecholamines (through E α and β receptors),
• the presence of GH (permissive),
• sympathetic effects,
• stress.

Inhibitory effects on glucagon secretion:

• a high blood Glu level (hyperglycemia),
• Somatostatin
• insulin (inhibits mRNA),
• hormonal effects.

The effects of glucagon:

• In the liver:
  • glycogenolysis ­,
  • gluconeogenesis ­,
  • ketogenesis ­,
  • cAMP level ­.
• In the adipose tissue:
  • lipolysis ­.