1. Indices of pancreatic mass and bacterial counts for jejunal and ileal mucosa were studied in rats after 3, 6, 10 and 15 days of total parenteral nutrition and compared with the results from orally fed and sham intravenously fed control rats.
2. Pancreatic wet weight corrected for body weight decreased significantly by 31–42% after 3, 6, 10 and 15 days of total parenteral nutrition. The most striking decrease occurred within 3 days. Other indices of pancreatic mass (protein and DNA) showed a similar pattern suggesting pancreatic hypoplasia. There was more DNA per g of pancreas, indicating that unless there were changes in tissue water cellular hypotrophy must have accompanied the hypoplasia.
3. Pancreatic RNA also decreased significantly after 3–10 days of total parenteral nutrition, suggesting reduced protein synthesis.
4. Bacterial counts (log number) whether expressed as number/unit length of intestine or number/g wet weight of mucosa were decreased for anaerobic bacteria in the jejunum after 3–15 days of total parenteral nutrition. In the ileum both aerobic and anaerobic bacteria increased after 6 days of parenteral nutrition and then decreased significantly.
5. The changes in bacterial flora are unlikely to account for the adaptive hypoplasia seen in the intestine of intravenously fed rats.