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Diabetes, Vol 40, Issue 1 95-101, Copyright © 1991 by American Diabetes Association
Nutrition and somatomedin. XXIII. Molecular regulation of IGF-I by amino acid availability in cultured hepatocytes
JB Harp, S Goldstein and LS Phillips
Division of Endocrinology and Metabolism, Emory University School of Medicine, Atlanta, GA 30303.
The poor growth associated with protein-calorie malnutrition occurs despite
circulating growth hormone levels that are normal or elevated and is
thought to be mediated partly by blunted generation of insulinlike growth
factor I (IGF-I) in the liver. To explore underlying mechanisms, we asked
whether altered availability of amino acids could regulate hepatic IGF-I
release independent of the contributions of regulatory hormones. Normal rat
hepatocytes were isolated by collagenase digestion and maintained in
serum-free medium with fixed concentrations of insulin and dexamethasone.
Levels of immunoassayable albumin and IGF-I accumulation in daily changes
of medium were sustained for 3-5 days, and all studies were performed
within this period. Cellular viability and content of DNA were unaffected
by deprivation of the essential amino acids lysine or tryptophan and the
nonessential amino acids cysteine and/or cystine. However, deletion of
tryptophan or lysine from the culture medium led to 63 and 76% declines in
IGF-I release, respectively (both P less than 0.001 vs. complete medium),
although omission of cysteine or cysteine plus cystine produced no
significant change. Over 5 days of culture, release of albumin was
maintained in complete medium, but omission of tryptophan depressed albumin
release over days 2-5 (P less than 0.001). In complete medium, IGF-I
release rose for 3 days and then declined. In tryptophan-deficient medium,
IGF-I levels were comparable to control values after 24 h but did not rise
at 48 h and then fell rapidly after 72 h in culture, with values
significantly below levels in complete medium (all P less than
0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

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Copyright © 1991 by the American Diabetes Association.
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