Ontogeny of the porcine insulin-like growth factor system.
The developmental expression of the individual components of the insulin-like growth factor (IGF) system in pigs was examined. Serum IGF-I and IGF-binding protein-3 (IGFBP-3) levels were low during fetal life and increased during postnatal development. Levels of mRNAs encoding these proteins were not greater for liver than for nonhepatic tissues (skeletal muscle, lung, kidney) and did not increase during the postnatal period, whereas hepatic growth hormone (GH) receptor mRNA expression was increased postnatally. Serum IGF-II levels exceeded IGF-I levels at all developmental stages examined and both exhibited postnatal increases. IGF-II mRNA abundance, in contrast, was high in the fetal tissues with the exception of lung and declined during the perinatal transition. Hepatic IGFBP-2 mRNA and serum IGFBP-2 levels increased during the latter half of gestation and then declined postnatally. The levels in muscle and liver of type I IGF receptors and the corresponding mRNAs also exhibited postnatal decreases. The discordance of changes in hepatic IGF-I and IGF-II mRNA abundance with serum IGF levels during the postnatal period does not support the concept that liver is the primary endocrine source of IGFs in the young pig. The postnatal increases in serum IGF levels may reflect decreased plasma clearance rates of these peptides which may be related to the transition in IGFBP type from IGFBP-2 to IGFBP-3 in blood and the reduced tissue expression of IGF receptors.
Lee
C Y
CY
Department of Dairy Science, University of Florida, Gainesville.
Chung
C S
CS
Simmen
F A
FA
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D004247:DNA; D005314:Embryonic and Fetal Development; D005786:Gene Expression Regulation; D018971:Insulin-Like Growth Factor Binding Protein 2; D018969:Insulin-Like Growth Factor Binding Proteins; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis* / Q000235:genetics; D017527:Receptor, IGF Type 2 / Q000096:biosynthesis* / Q000235:genetics; D013002:Somatomedins / Q000096:biosynthesis* / Q000235:genetics; D013552:Swine / Q000196:embryology / Q000254:growth & development*
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D017527:Receptor, IGF Type 2; D013002:Somatomedins; D004247:DNA; D017526:Receptor, IGF Type 1