Effects of energy and purines in the diet on proliferation, differentiation, and apoptosis in the small intestine of the pig.

The effects of the energy and purine content in the diet on mucosal cell mitosis, function, and apoptosis in the small intestine of pigs were investigated in two experiments. In experiment I, three groups of five pigs were first fed a commercial diet that contained 9.1 MJ metabolizable energy (ME) per kilogram dry matter (DM) and 16.4% crude protein. It was followed by the experimental diets for 5 days each starting with an energy deficit (5.8 MJ ME/kg DM; 7% crude protein) followed by a high-energy diet with low purine content (14.1 MJ ME/kg DM; 13.6% crude protein; 460 mg purines/kg), or alternatively an isocaloric high-purine diet (2,160 mg purines/kg). During experimental periods, blood samples were drawn daily through catheters for insulin-like growth factor-I (IGF-I) determination. The animals were killed at the end of the corresponding feeding period and gut tissue samples were collected. In tissue samples, IGF-I and parameters for the characterization of mitosis (thymidine kinase [TK], proliferating-cell nuclear antigen [PCNA]) and differentiation (RNA content, alkaline phosphatase, sucrase) were measured. The degree of apoptosis was determined histologically. In experiment II, five pigs were fitted with simple T-cannula at the distal jejunum. They were fed the three experimental diets consecutively for 7 days each and sucrase and alkaline phosphatase were measured in digesta (four samples daily). IGF-I in blood but not in tissue clearly responded to the energy content of the diet with a decrease during the deficit and an increase in the two high-energy groups. However, purines had no additional effect on IGF-I. TK, PCNA, and gut weight showed an energy effect on mitosis, which was paralleled by increased peripheral IGF-I. Purines led to a further increase of mitosis, but IGF-I and gut weight were not increased. The degree of mitosis was correlated with higher activities of sucrase and alkaline phosphatase and also with the number of apoptotic cells. The enzyme activity increased from the deficit to the high-energy group and was further elevated due to purines. The results from experiment II also confirm these effects of energy and purines, because the activities of the enzymes in digesta decreased during energy deficit, but increased due to energy and in addition to purines.