Characterization of the IGF system in food-restricted pregnant and lactating rats: Role of IGF-I in nutrient partitioning
Monaco, Marcia Helena
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Permalink
https://hdl.handle.net/2142/22886
Description
Title
Characterization of the IGF system in food-restricted pregnant and lactating rats: Role of IGF-I in nutrient partitioning
Author(s)
Monaco, Marcia Helena
Issue Date
1995
Doctoral Committee Chair(s)
Donovan, Sharon M.
Department of Study
Food Science and Human Nutrition
Discipline
Food Science and Human Nutrition
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Animal Culture and Nutrition
Health Sciences, Nutrition
Language
eng
Abstract
Metabolic and behavioral mechanisms have been implicated in the development of adaptive strategies to suboptimal nutrition. However, very little is known about the underlying endocrine mechanisms involved in this adaptation. To investigate the role of the IGF-I in adaptation to dietary restriction, the experiments reported herein determined the changes in the circulating levels, as well as, in the gene expression of IGF-I and IGFBPs in pregnant and lactating rats which were food restricted during pregnancy and lactation or solely during lactation. In addition, the effects of IGF-I administration on amino acid uptake was investigated using an alanine analogue.
The food-deprivation model used in these studies was comparable to the average percent energy (60%) of the RDA consumed by lactating women living in different areas of the world. Food restriction during pregnancy and lactation was associated with marked changes in the profiles of serum IGF-I and IGF-binding proteins. IGF-I binding to carrier proteins shifted from the high molecular weight complex to low molecular weight binding proteins (IGFBP-1 and -2). Serum IGFBP-1 and -2 potentially increased IGF-I availability by enhancing IGF-I clearance from serum to peripheral tissues. IGFBP-1 and -2 gene expression tended to be elevated in restricted animals, confirming that food restriction induced hepatic synthesis of these two proteins. Hepatic IGF-I mRNA content also tended to be elevated in food restricted dams suggesting that there are signals up-regulating IGF-I transcription in food-restricted pregnant and lactating rats.
The effects of IGF-I on nutrient partitioning was studied using a non-metabolizable alanine analogue, $\alpha$-amino(1-$\sp{14}$C) isobutyrate. Raising serum IGF-I concentrations of restricted dams to control levels increased AIB uptake into muscle and mammary gland. The mechanisms by which IGF affects AIB accumulation remains to be established, but it may be that the mechanisms are tissue specific. In addition, AIB uptake differed between the two food-restricted groups, suggesting that animals may adapt differently to food-restriction, depending either upon the duration of the restriction and/or the level of maternal reserves which are available.
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