1. The short-term effect of oral feeding on albumin synthesis rate was investigated in 12 healthy volunteers using two meal regimens. Albumin synthesis was measured over 90 min after injection of a ‘flooding’ amount (43 mg/kg body weight) of phenylalanine enriched to 7.5, 10 or 15 atoms% with the stable isotope [ring-2H5]phenylalanine.
2. In one set of subjects, consumption of five small hourly meals resulted in a consistent and significant increase (P < 0.05) in albumin fractional synthesis rate from a mean (± SEM) fasting value of 5.8 (± 0.4)%/day to 7.1 (± 0.4)%/day in the fed state.
3. A second study in which albumin synthesis was measured 30 min after consumption of a single larger meal was carried out in another set of volunteers. The fractional rate of albumin synthesis was again significantly elevated after feeding (P < 0.05), rising from 7.1 (± 0.4)%/day in the fasted state to 9.1 (± 0.6)%/day in the fed state. In both studies, similar responses were observed in the absolute rate of albumin synthesis (mg day−1 kg−1).
4. Albumin secretion time was significantly shorter (P < 0.05) after feeding in both studies, suggesting that the acute stimulation in albumin synthesis observed after feeding may in part be mediated via a post-transcriptional mechanism.
5. The response of total liver protein synthesis to oral feeding was investigated in an animal model employing adult rats studied with a flooding amount of [2,6-3H]phenylalanine.
6. The results indicated a stimulation of 20% with no difference in the proportion of albumin synthesis relative to total liver synthesis, determined from the immunoprecipitation of albumin from the liver.