Jejunal mucosal protein synthesis: validation of luminal flooding dose method and effect of luminal osmolarity

To validate a system to study acute regulation of protein synthesis in intestinal mucosa by luminal nutrients, we compared the fractional rate of protein synthesis (K-s) in jejunal mucosa using the intravenous flooding dose technique with the administration of a comparable concentration and specific activity of tracer in a luminal perfusate. Routes of tracer administration and surgery and perfusion trauma had no effect on mucosal K-s. Furthermore, four 10-cm jejunal segments (within a piglet) simultaneously but separately perfused with a luminal flooding dose had similar K-s values (mean, 43 +/- 2%/day; P > 0.05). Nutrient solutions perfused through four intestinal segments within an animal did not affect plasma levels of most amino acids or glucose. Because cellular hydration is important in regulating metabolism, the effects of physiological variation in luminal osmolarity were studied. Luminal osmolarities between 250 and 380 mosM did not affect mucosal K-s. The system described allows multiple comparisons within an animal and provides a robust model to study acute modulation of protein synthesis in intestinal mucosa by luminal stimuli.