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Insulin-like growth factor-binding proteins in tissue fluids from the lamb
A P Lord1, A A Martin, P E Walton
1Department of Animal Sciences, Waite Agricultural Research Institute, University of Adelaide, Australia.
The Journal of Endocrinology
|April 1, 1991
Summary
This study characterizes insulin-like growth factor-binding proteins (IGFBPs) in sheep plasma, lymph, and cerebrospinal fluid. Differences were found in IGFBP profiles across these fluids and between different lymph types.
Area of Science:
- Endocrinology
- Proteomics
- Comparative Physiology
Background:
- Insulin-like growth factor-binding proteins (IGFBPs) modulate the bioavailability and activity of insulin-like growth factors (IGFs).
- Characterization of IGFBPs in various extracellular fluids is crucial for understanding IGF signaling pathways.
- Previous studies have focused primarily on plasma IGFBPs, with less known about their counterparts in lymph and cerebrospinal fluid (CSF).
Purpose of the Study:
- To characterize and compare insulin-like growth factor-binding proteins (IGFBPs) in ovine plasma, cerebrospinal fluid (CSF), and lymph from different lymph node types.
- To investigate the presence and molecular forms of IGFBPs in extracellular fluids relative to circulating plasma.
- To identify potential tissue-specific differences in IGFBP profiles within the lymphatic system.
Main Methods:
- Heparinized plasma, CSF, and lymph samples were collected from young lambs.
- Insulin-like growth factor-binding proteins (IGFBPs) were analyzed using ligand blotting and competitive binding assays with radiolabeled IGF-I, IGF-II, and des(1-3)IGF-I.
- Size exclusion chromatography (Superose 6) followed by ligand blotting was employed to analyze IGFBP complexes.
Main Results:
- Distinct IGFBP profiles were observed in ovine plasma, lymph, and CSF.
- An IGF-II-specific binding protein (~250 kDa), likely the soluble type-2 IGF receptor, was found in plasma and all lymph types.
- A 130 kDa complex, likely IGFBP-3 bound to the acid-labile subunit, was prominent in plasma and intestinal lymph.
- Multiple IGFBP bands (52, 46, 32, 28, 23.5 kDa) were detected in plasma and lymph, with an additional IGF-II-specific band (22 kDa) in prescapular and popliteal lymph.
- CSF showed a unique profile, lacking the 52/46 kDa bands and with a predominant 35 kDa binding protein that did not significantly bind des(1-3)IGF-I.
Conclusions:
- Significant qualitative and quantitative differences exist in the IGFBP profiles of ovine plasma, lymph, and CSF.
- Marked variations in IGFBP composition were observed among intestinal, prescapular, and popliteal lymphs.
- These findings suggest tissue-specific release of binding proteins into extracellular fluids, contributing to regional IGF signaling regulation.