Effect of hibernation and jejunal bypass on mucosal structure and function

Intestinal mucosal structure and function may be regulated by systemic factors associated with oral feeding, as well as local responses initiated by contact of the mucosa with food. This study compared the relative effects of these factors in an animal model that undergoes seasonal long-term fasting. Jejunal bypass operations or sham surgeries were performed on active fed ground squirrels or on squirrels that subsequently ceased feeding and hibernated. Mucosal wet weight, protein content, villus height, and surface area were reduced in jejunal segments that had minimal exposure to luminal contents (bypassed segments of active squirrels and all segments of hibernators) compared with segments exposed to the luminal stream (incontinuity and sham segments of active squirrels). When normalized to mucosal weight, transepithelial absorption of 3-O-methylglucose and alanine-dependent sodium flux were greater in jejunal segments with minimal exposure to luminal nutrients. Altered structure in bypassed segments of active and hibernating squirrels paralleled changes in functional parameters despite the presence of different systemic factors in the two groups. Thus, in this animal model, contact of the mucosa with food, and not systemic factors associated with oral feeding, is the primary factor maintaining mucosal mass. The absence of mucosal contact with nutrients enhances specific absorptive function by mechanisms that have yet to be determined.