Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 47

 GGT resides in the cell membranes of all somatic cells, but its greatest activity is in biliary epithelial cells, pancreatic acinar cells, and renal tubular epithelial cells.

 GGT is a cell surface glycoprotein and is a liver canalicular enzyme, and it is induced by dilation of the biliary tree.

 It has multiple functions including the regulation of the anti‐oxidant glutathione.

 Increased GGT activity in serum is usually an indication of hepatobiliary toxicity, especially cholestasis.

 Bile accumulation (cholestasis), biliary hyperplasia, and some drugs (e.g. phenobarbital, furosemide, phenytoin, and cimetidine) increase serum GGT activity.

 GGT has a long half‐life (approximately three days), thus serum concentrations fall slowly after an episode.

 Chronic liver disease associated with hepatocyte destruction, fibrosis, and biliary hyperplasia are associated with severe increases in GGT.

 Right dorsal displacement of the colon causes an increase in serum GGT activity by impeding the outflow of bile.

 Proximal enteritis causes increases in AST and GGT activity secondary to ascending infection of the biliary tract and/or liver damage from systemic effects such as endotoxemia and hypovolemia.

 Reference range: Adult horses 6–30 U/l.

 The normal range for burros, donkeys and asses may be 2–3 times higher, and mules and hinnies may be two times higher than values for horses.

  Foals have a higher reference range than adults for the first one to two months of life.Unlike in ruminant neonates, this is not due to ingestion of colostrum as GGT activity is low in mare's colostrum.The increased serum GGT activity in foals in the first month of life seems to be due to endogenous sources.Note: Idiopathic increases in GGT occasionally occur in young, apparently healthy Thoroughbred horses. The cause is unknown. These horses may exhibit poor performance.