Tuesday, November 13, 2012

COUNTER REGULATORY HORMONES TO INSULIN


These hormones act antagonistically to insulin thereby increasing glucose concentration. The initial response (within minutes) to low glucose is an increase in glucose production, stimulated by glucagon and epinephrine. With time (3 to 4 hours), growth hormone and cortisol increase glucose mobilization and decrease glucose utilization. To maintain glucose concentration glucagon is the most important, and epinephrine is critical when glucagon is deficient.
GLUCAGON: 
It is a 29 amino acid polypeptide hormone secreted by alpha cells of the pancreas. The major target is liver where it binds to specific receptors and increase both intracellular AMP and calcium. Glucagon stimulates liver glycogenolysis and gluconeogenesis and also enhances liver ketogenesis. Another minor target is adipose tissue where it increases lipolysis. Glucagon is regulated primarily by plasma glucose concentration. Insulin inhibits glucagon release and decreases glucagon gene expression. Increased glucagon concentration, secondary to insulin deficiency, is believed to contribute to the hyperglycemia and ketosis of diabetes. Food ingestion stimulates release of glucagon like peptide I, which acts on the beta cell of the pancreas to stimulate insulin gene transcription and potentiates glucose induced insulin secretion.
EPINEPHRINE: 
It stimulates glycogenolysis and decrease glucose use, thereby increasing blood glucose. It also stimulates glucagon secretion and inhibits insulin secretion. This hormone is released during stress to produce glucose for energy.
GROWTH HORMONE: 
It is secreted by anterior pituitary gland and stimulates gluconeogenesis, enhances lipolysis and antagonizes insulin-stimulated glucose uptake.
CORTISOL:
It stimulates gluconeogenesis and increases breakdown of protein and fat. E.g. patients with Cushing’s syndrome have higher cortisol and are hyperglycemic.

OTHER HORMONES: 

Thyroxine stimulates glycogenolysis, increase gastric emptying and intestinal glucose absorption. Somastostatin (called growth hormone-inhibiting hormone) is a peptide hormone found in GIT, the hypothalamus and delta cell of pancreas. It inhibits release of growth hormone from pituitary. It also inhibits secretion of glucagon and insulin by pancreas. 
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