Seasonal changes in mucosal structure and function in ground squirrel intestine.

Seasonal variations in mucosal structure and transport function were examined in active and hibernating ground squirrel jejunum. Mucosal wet weight and protein content, villus height, and mucosal surface area were lowest in hibernators, increased in spring, peaked in summer, and declined in fall. Transepithelial electrical parameters and net Na+ and 3-O-methylglucose (3-OMG) absorption measured in flux chambers were greatly reduced in hibernator tissues tested at 7 degrees C compared with tissues from hibernators or active squirrels studied at 37 degrees C. At 37 degrees C, net Na+ and 3-OMG absorption normalized to serosal surface area was similar in tissues from all squirrels. When normalized to mucosal surface area, absorption in hibernators was greater than in spring or summer squirrels but was not significantly different from fall values. Absorption normalized to mucosal area was similar among spring, summer, and fall squirrels. Increases in short-circuit current evoked by mucosal addition of D-glucose or L-alanine were significantly greater in hibernators than in fall squirrels. These results demonstrate seasonal variations in mucosal structure and transport function in captive ground squirrels. Enhanced area-specific absorption in hibernator tissues at 37 degrees C may represent a compensatory response to pronounced mucosal atrophy that occurs during hibernation.