Serum concentrations of insulin-like growth factor II are not changed by short-term fasting and refeeding.
To determine the factors that regulate insulin-like growth factor II (IGF-II), we raised polyclonal antibodies to this peptide and developed a RIA that measures IGF-II in serum or plasma samples after extraction of IGF-binding proteins by C18 cartridge chromatography. The IGF-II antiserum was highly specific, exhibiting no cross-reactivity with IGF-I or insulin at the highest concentrations tested (10(-6) mol/L). As little as 0.43 micrograms/L IGF-II was detectable, and 50% displacement of tracer occurred at 1.7 microgram/L. The serum IGF-II concentrations of normal adults [mean, 634 +/- 170 (+/- SD) micrograms/L], patients with acromegaly (570 +/- 146 micrograms/L), and patients with hypopituitarism (156 +/- 58 micrograms/L) were similar to those reported by others. In eight obese subjects injected with GH (0.1 mg/kg ideal BW, im, every 48 h for 16 days), serum IGF-II concentrations did not rise significantly, whereas IGF-I concentrations increased 67%. Sixteen normal subjects, within 15% of ideal body weight, were fasted for 5 days on two to four occasions and refed diets of differing protein and calorie contents. Their mean serum IGF-II concentration before fasting (691 +/- 26 micrograms/L) was not significantly different from that after fasting (674 +/- 21 micrograms/L) or after refeeding (641 +/- 20 micrograms/L). In contrast, their mean IGF-I concentration decreased 42% with fasting and rose with refeeding. Unlike IGF-I, serum IGF-II concentrations do not appear to be regulated by short term changes in nutritional status. It is clear from this study and others that IGF-II and IGF-I are regulated differently despite their structural homology and the similarity of their actions in vitro.
Davenport
M L
ML
Department of Pediatrics, Chapel Hill 27599.
Svoboda
M E
ME
Koerber
K L
KL
Van Wyk
J J
JJ
Clemmons
D R
DR
Underwood
L E
LE
D000328:Adult; D004435:Eating; D005215:Fasting; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011863:Radioimmunoassay; D012016:Reference Values; D013002:Somatomedins / Q000097:blood*
D013002:Somatomedins; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone