A single food bolus stimulates albumin synthesis in growing piglets.

Background: A stable isotope tracer method to quantify the synthesis of proteins of hepatic origin in response to feeding is described. The response of albumin synthesis on one mixed meal in a piglet model was investigated and the intragastric and intravenous administration modes of 13C-valine were compared.

Methods: The fasting and postprandial fractional synthesis rates (FSRs) of albumin in 15 piglets were measured while infusion rates of 13C-valine were changed in anticipation of the increased appearance of the tracee after a single liquid food bolus (30 mL/kg infant formula). 13C-valine enrichments in albumin hydrolysates at regular time intervals were determined with gas chromatography-combustion isotope ratio mass spectrometry.

Results: The intravenous mode (n = 8) showed constant plasma alpha-ketoisovalerate tracer-to-tracee ratios (coefficient of variation range: 1-8%), and a 27% increase in albumin FSR after the food bolus (mean FSR +/- standard error [SE]: fasting 14.4% +/- 1.6% vs. postprandial 18.3% +/- 2.2% per day; P < 0.005). In the intragastric mode (n = 7), albumin FSR calculated from the mean precursor values increased 32% after feeding (fasting 14.6% +/- 1.5% vs. postprandial 19.3% +/- 1.6% per day; P = 0.005), despite absence of constant alpha-ketoisovalerate enrichment (coefficient of variation range: 15-31%). The FSRs were not significantly different between both infusion modes.

Conclusions: A mixed food bolus increases albumin FSR in growing piglets by approximately 30%, irrespective of the tracer administration route. The concept of anticipated precursor steady state is applicable to study changes of hepatic protein synthesis after a single meal. The intragastric mode of tracer administration can be applied as a less invasive method to measure tissue specific protein synthesis in children.