Effect of Sera from Fed and Fasted Pigs on Proliferation and Protein Turnover in Cultured Myogenic Cells

Abstract

The effects of fasting on the ability of swine serum to affect proliferation, protein synthesis and protein degradation in L6 myoblast cell culture bioassays were evaluated. Barrows (15 to 20 kg) were fitted with jugular catheters. Blood samples were collected at four evenly spaced intervals between 0800 and 1700 on collection days. Prefast blood samples were obtained on d 1 and 2 of the study, after which pigs were subjected to a 5-d fast. Fasted samples were obtained on the 1st, 3rd and 5th d of the fast (d 3, 5 and 7 of the study). Serum from each collection day was pooled and tested in the proliferation bioassay for each pig. Prefast and fasted serum pools were formed by pooling prefast days (1 and 2) or fasted days (3, 5 and 7), respectively, from all pigs in a study. These pools were tested in the proliferation and protein turnover bioassays as well as in a Somatomedin-C (SmC) radioimmunoassay. Serum from the fasted collection days showed a decrease in mitogenic activity compared with serum from the two prefast days (P<.001). At high concentrations, sera obtained from fasted pigs inhibited muscle cell proliferation (P<.001). Additionally, adding fasted serum to control swine serum (CSS) inhibited the mitogenic activity of CSS in a dose-dependent manner (P<.025). Therefore, fasted sera showed a decreased ability to promote muscle cell proliferation and, in addition, appeared to contain a factor(s) that inhibits muscle cell proliferation. Fasted serum also caused a 21.6% increase in protein degradation compared with prefast serum. There was no difference in the effect of prefast or fasted serum on protein synthesis. Fasting decreased serum SmC levels by 80% compared with prefast serum levels.