Effect of weaning at different ages on serum insulin-like growth factor I (IGF-I), IGF binding proteins and serum in vitro mitogenic activity in swine.
We investigated the effects of weaning or fasting of 21- or 35-d-old swine by monitoring serum mitogenic activity, circulating insulin-like growth factor I (IGF-I) and its binding proteins using L6 myoblast bioassays, RIA and ligand blotting techniques. Serum samples were collected from 21- or 35-d-old animals just before and 36 h after weaning or fasting. Sera from 21- and 35-d-old weaned animals were not significantly altered in their ability to promote myoblast proliferation, whereas sera from 21- and 35-d-old fasted animals caused 29 and 21% decreases (P less than .05) compared with preweaning. The mitogenic activity of control serum was inhibited by serum from fasted animals but not by preweaned or weaned sera. Serum IGF-I levels were decreased 65 to 70% (P less than .05) with weaning or fasting at both ages. Unoccupied binding sites on circulating IGF binding proteins in the 155 kDa range decreased 18 to 19% with weaning at both ages and decreased 40% (P less than .05) with fasting at 21 d but only 17% at 35 d. Ligand blotting revealed that the 43 and 39 kDa IGF binding protein bands decreased with weaning and fasting at both ages, whereas the 29-kDa band increased with weaning and fasting. These data indicate that serum IGF-I and specific IGF binding protein bands decrease during weaning or fasting at 21 and 35 d of age. However, serum mitogenic activity did not always follow serum IGF-I levels.
White
M E
ME
Dept. of Anim. Sci., Ohio State Univ., Columbus.
Ramsay
T G
TG
Osborne
J M
JM
Kampman
K A
KA
Leaman
D W
DW
D000367:Age Factors; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis*; D002455:Cell Division; D002999:Clone Cells; D004435:Eating; D007106:Immune Sera / Q000276:immunology; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008934:Mitogens; D009132:Muscles / Q000166:cytology*; D011863:Radioimmunoassay; D014886:Weaning
D002352:Carrier Proteins; D007106:Immune Sera; D018969:Insulin-Like Growth Factor Binding Proteins; D008934:Mitogens; D007334:Insulin-Like Growth Factor I