Insulin

 
• Hormonal
o Growth hormone, corticosteroids and thyroxine modify insulin release in response to glucose
o PGE inhibit insulin release
o Somatostatin evokes release of both insulin and glucagon
o Glucagon evokes release of insulin as well as somatostatin
o Insulin inhibit glucagon secretion. Amylin released with insulin, inhibit glucagon secretion through a central site if action in the brain
 
• Neural
o Adrenergic α2 receptor activation decreases insulin release by inhibiting β cell adenylyl cyclase
o Cholinergic- muscarinic activation by Ach or vagal stimulation causes insulin secretion through IP3/DAG increased intracellular Ca2+ in the β cells.
 
Action of insulin
1. Insulin facilitates glucose transport across cell membrane; skeletal muscle and fat are highle sensitive
2. Phosphorylation of glucose to glucose-6-phosphate is enhanced by insulin through increased production of glucokinase. Insulin facilitates glycogen synthesis from glucose in liver, fat and muscle by stimulating glycogen synthase. It inhibits glycogenolysis in liver.  
3. Insulin inhibits gluconeogenesis in liver by gene mediated decreased synthesis of phosphoenol pyruvate carboxykinase
4. Insulin inhibits lipolysis in adipose tissue and favors triglyceride synthesis.
5. Insulin enhances transcription of vascular endothelial lipoprotein lipase and thus increases clearance of VLDL and chylomicrons
6. Insulin facilitates AA entry and their synthesis into proteins, as well as inhibits protein breakdown in muscle and most other cells