Effects of oral administration of insulin-like growth factor-I on circulating concentration of insulin-like growth factor-I and growth of internal organs in weanling mice.
Insulin-like growth factor (IGF)-I is a polypeptide that mediates the growth-promoting action of growth hormone in postnatal animals. The present study was conducted to examine whether orally administered IGF-I would be absorbed into the general circulation and also whether ingested IGF-I would enhance the growth of whole body as well as internal organs, and tissues in 3-week-old ICR-strain female weanling mice. In experiment (Exp) 1, a total of 70 mice received IGF-I orally at 1 microg.g-1 in 0.2-ml PBS or the vehicle alone. Concentrations of IGF-I and glucose in heart blood were measured after killing 5 animals in each group every fourth hour during a 24-hour period. In Exp 2, a total of 40 mice received oral IGF-I administration at 1 microg.g-1 or vehicle every third day beginning from day 0 for a 13-day period. Half the animals were killed at day 7 and the other half at day 13. Weights of whole body and organs/tissues (small intestine, liver, thigh muscle, and brain) were measured every day and at slaughter, respectively. In Exp 1, following the oral IGF-I administration, serum IGF-I concentration increased at hour 4 (p<0.01) and returned to the hour 0 level by hour 8, whereas glucose concentration was lowest at hour 4 and returned to the hour 0 level by hour 16. In the PBS-fed group, neither IGF-I nor glucose concentration changed during the 24-hour period. In Exp 2, weight of small intestine increased (p<0.05) in response to the oral IGF-I, whereas weights of liver and thigh muscle of the IGF-I-fed group were greater (p<0.01) and tended to be greater (p=0.06), respectively, than those of the PBS-fed only at day 13. However, brain weight and serum concentrations of IGF-I and IGF-II were not affected by oral IGF-I administration. Results suggest that although orally administered IGF-I mainly acts at the intestine, a portion of ingested IGF-I is absorbed into the general circulation to enhance the growth of selective organs/tissues in weanling mice.
Kim
W K
WK
Division of Life Science and Genetic Engineering, College of Life and Environmental Sciences, Korea University, Seoul, Republic of Korea.
Ryu
Y H
YH
Seo
D S
DS
Lee
C Y
CY
Ko
Y
Y
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D001921:Brain / Q000254:growth & development; D006128:Growth / Q000187:drug effects*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage* / Q000032:analysis*; D007335:Insulin-Like Growth Factor II / Q000032:analysis; D007421:Intestine, Small / Q000254:growth & development; D008099:Liver / Q000254:growth & development; D051379:Mice; D008813:Mice, Inbred ICR; D018482:Muscle, Skeletal / Q000254:growth & development; D009929:Organ Size / Q000187:drug effects; D014886:Weaning
D001786:Blood Glucose; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II