The exocrine pancreas is the larger of the two parts that make up the pancreas. It consists of tubuloacinar glands that primarily manufacture and secrete digestive enzymes that break down food in the intestine so it can be absorbed.
In this case, AFGPs are secreted into the intestinal lumen where they protect the intestinal fluid from being frozen by ice crystals that come in with seawater and food. Internal fluids in notothenioids are about one-half as salty as seawater.
While seawater reaches its freezing point at ?.91 degrees Celsius, fish fluids freeze at about ? degree Celsius. These species dwell in water that rarely rises above the freezing point and is regularly filled with ice crystals.
From the intestine, the AFGPs are, apparently, absorbed into the blood. This hypothesis is based on the near-identical composition and abundance of AFGPs found in the fish serum.
"In this comprehensive study, we confirm that the exocrine pancreas is the major AFGP synthesis site in Antarctic notothenioid fishes from hatching through adulthood, while the liver is AFGP-expression null in all life stages," the researchers conclude. "Because the notothenioids are confined to chronically icy Antarctic waters, and face high risks of ice inoculation from frequent seawater drinking, the evolution of AFGPs in these fishes was probably driven first and foremost by the need to prevent the hyposmotic intestinal fluid from freezing."
The researchers also studied a variety of fishes from Arctic waters that have liver expression of AFGPs, and found that all of them also express antifreeze in the pancreas.
Source:University of Illinois at Urbana-Champaign