Changes in proliferation and surface morphology in the rat ileum in response to total parenteral nutrition

To find out how the ileum adapts to total parenteral feeding, two experiments were performed. In the first experiment rats were given total intravenous feeding for 10 days. The animals were injected with tritiated thymidine (1 μCi/g body weight) 1 hour before being killed. Portions of the ileum were used for (1) radioautography, (2) analysis of the tissue DNA content, (3) specific activity of the DNA, and (4) scanning electron microscopy. The DNA content of ileum was decreased 72% while the specific activity of DNA was increased 289% in the I.V. fed rats. In the second experiment rats were given total intravenous feeding for 10 days. The animals were injected with colchicine (1 mg/kg body weight) 3 hours before being killed. The number of labelled cell nuclei per ileal crypt section was significantly decreased by parenteral feeding as was the number of colchicine collected metaphase figures. Light microscopy revealed the crypt and the villus height to be shorter and the number of goblet cells per unit surface area to be increased in parenterally fed rats as compared to those fed solid food orally. Enterocytes of the exfoliative zone from the ileal villi of rats fed solid food showed three distinct types of surface architecture whereas those from I.V. fed rats all possessed abundant microvilli. No bacteria were seen in ilea of I.V. fed animals but many were seen embedded in enterocytes from orally fed rats. Because the amount of DNA per cell is known to be constant, we concluded that the overall number of cells in the ileum decreased about 72% in the I.V. fed rats and that cell proliferation in the crypts, although significantly decreased, was still supporting an epithelial renewal process.