Luminal and systemic signals trigger intestinal adaptation in the juvenilepython

Juvenile pythons undergo large rapid upregulation of intestinal mass and in testinal transporter activities upon feeding. Because it is also easy to do surgery on pythons and to maintain them in the laboratory, we used a pytho n model to examine signals and agents for intestinal adaptation. We surgica lly isolated the middle third of the small intestine from enteric continuit y, leaving its mesenteric nerve and vascular supply intact. Intestinal cont inuity was restored by an end-to-end anastomosis between the proximal and d istal thirds. Within 24 h of the snake's feeding, the reanastomosed proxima l and distal segments (receiving luminal nutrients) had upregulated amino a cid and glucose uptakes by up to 15-fold, had doubled intestinal mass, and thereby soon achieved total nutrient uptake capacities equal to those of th e normal fed full-length intestine. At this time, however, the isolated mid dle segment, receiving no luminal nutrients, experienced no changes from th e fasted state in either nutrient uptakes or in morphology. By 3 days postf eeding, the isolated middle segment had upregulated nutrient uptakes to the same levels as the reanastomosed proximal and distal segments, but it stil l lacked any appreciable morphological response. These contrasting results for the reanastomosed intestine and for the isolated middle segment suggest that luminal nutrients and/or pancreatic biliary secretions are the agents triggering rapid upregulation of transporters and of intestinal mass and t hat systemic nerve or hormonal signals later trigger transporter regulation but no trophic response.