Altered lipid metabolism during enteral or parenteral nutrition in rats: comparison with oral feeding

To investigate the effects of different routes of alimentation on lipid metabolism, lipid-free nutrients with the same amount of energy and composition were continuously administered via the oral cavity (oral group), directly to the stomach (enteral group), or into the superior caval vein (parenteral group) of unrestrained rats. The body weight gain 1 week after continuous nutrition was greater in enteral and parenteral groups than in the orally-fed group. In comparison with the orally-fed group, the enterally-fed group had significantly greater liver and retroperitoneal adipose tissue weights and hepatic lipid content, whereas the parenterally-fed group produced similar changes to those in the enteral group without significant accumulation of hepatic lipid. The rate of fatty acid synthesis after 1 week of alimentation was 3-fold higher in the liver in enterally-fed group, and approximately 10-fold higher in white adipose tissue in both enterally- and parenterally-fed groups than in orally-fed group. Plasma concentrations of catecholamines after 6 h were significantly higher in the orally-fed group than in either the enteral or parenteral group. However, plasma insulin concentrations were not significantly different among the three groups. The results indicate that lipid synthesis and its deposition in the liver and adipose tissue are greatly influenced by the route of alimentation, possibly owing to difference in the early neuro-hormonal responses to different routes of alimentation.