Pancreatic enzymes Flashcards
What is lipase?
A single-chain glycoprotein enzyme that hydrolyze glycerol esters of long-chain fatty acids. A 2 step process - cleaving off the 1st two fatty acids is easy, but steric hindrance prevents cleavage of beta-monoglyceride. This spontaneously isomerises into the alpha form 3-acylglycerol which permits the 3rd fatty acid to be split off.
Requirements for lipase to work most effectively
Bile salts and colipase.
Hormonal regulation of lipase secretion?
CCK and secretin (also regulate bile salt and colipase secretion)
How does serum lipase concentration change after an attack of acute pancreatitis?
Rises within 4-8 hours, peaks at 24 hours, decreases within 7-14 days. Increase between 2 and 50 x URL. Not necessarily proportional to severity of the attack
Advantage(s) of lipase over amylase
More specific (once 3x URL)
Remains increased for longer than amylase.
Causes of increase in lipase
Acute pancreatitis
Obstruction of pancreatic duct (calculus, carcinoma)
Reduced GFR
Macrolipase
ERCP
Opiates (causes Sphincter of Oddi to contract)
Methods for lipase measurement
Multiple methods in use which are poorly standardised, resulting in very different results by different methods and the potential to cause clinical confusion if serial results are obtained from different analysers.
Titrimetric - time consuming and labour intensive although automated methods have been developed
Turbidimetric - Unreliable (increase instead of decrease in turbidity sometimes occurs) and limited method linearity which limits reportable range to only 3x URL
Numerous enzymatic methods with the advantage of small sample volume requirements, good precision, wide dynamic range and ease of automation.
Dry chemistry slide method - more specific for intestinal than pancreatic lipase and subject to interference by postheparin lipase and pancreatic carboxylesterase.
What is amylase?
A calcium metalloenzyme - calcium essential for functional integrity; anions (chloride and bromide most effective) required for activation.
Amylase isoforms?
Two true isoenzymes: Salivary and pancreatic
Salivary amylase has glycosylated and deglycosylated isoforms which can be separated by iso-electric focusing or electrophoresis.
Significance of P-amylase deficiency
Genetic defect resulting in carbohydrate malabsorption (abdo distension, flatulence, loose stools, poor weight gain).
