Orally administered iodinated recombinant human insulin-like growth factor-I (125I-rhIGF-I) is poorly absorbed by the newborn piglet.
BACKGROUND
The purpose of the current study was to determine the degree to which milk-borne insulin-like growth factor-I (IGF-I) is absorbed.


METHODS
Cesarean-derived piglets were fitted with umbilical arterial and venous catheters within 2 h of birth and were administered formula containing 21.7 +/- 1.8 microCi of iodinated recombinant human IGF-1 (125I-rhIGF-I) by orgogastric gavage. Blood samples were taken before administration of the 125I-rhIGF-I (t0) and for 4 h postgavage. Plasma was obtained by centrifugation and total and trichloroacetic acid precipitable radioactivity were determined. Immunoreactive 125I-rhIGF-I was assessed using a polyclonal antibody to human IGF-I. Four hours after feeding, intestines were removed, divided into 13 segments, and flushed with saline. Radioactivity within the small intestinal lumen and wall were measured.


RESULTS
Radioactivity in portal blood was higher than t0 at all times points (p < 0.05), whereas arterial radioactivity did not differ from t0 until 30 min postgavage. On average 18-20% of total radioactivity in both portal and arterial blood was acid-precipitable, with the proportion decreasing over time (p < 0.001). Immunoprecipitable radioactivity averaged 3-5% of the total radioactivity and was higher in portal than arterial blood (p < 0.05). Based on a plasma volume of 0.062 +/- 0.005 L and a baseline plasma IGF-I concentration of 1.81 +/- 0.56 nmol/L, absorbed 125I-rhIGF-I represented 0.205% of the total plasma IFG-I pool, whereas 14% of the dose was associated with the lining of the intestine.


CONCLUSIONS
Absorption of orally administered IGF-I does not contribute significantly to circulating IGF-I.
Donovan
S M
SM
Department of Food Science and Human Nutrition, University of Illinois, Urbana 61801, USA.
Chao
J C
JC
Zijlstra
R T
RT
Odle
J
J
D000284:Administration, Oral; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western / Q000379:methods; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000097:blood; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics*; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008024:Ligands; D008892:Milk / Q000737:chemistry; D011863:Radioimmunoassay; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics; D013552:Swine; D013997:Time Factors
D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D008024:Ligands; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I