Insulin-like growth factor-binding proteins in hypophysectomized rat liver: characterization and subcellular...

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Insulin-like growth factors (IGFs) play crucial roles in growth and metabolism.
• IGF binding proteins (IGFBPs) modulate IGF bioavailability and activity.
• Hepatic IGF binding is complex and influenced by subcellular localization.

Purpose of the Study:

• To characterize IGF binding proteins in rat hepatic subcellular fractions.
• To investigate the role of these binding proteins in IGF-II receptor interactions.
• To understand how hypophysectomy affects hepatic IGF binding.

Main Methods:

• Characterization of IGF binding proteins in hepatic subcellular fractions and supernatants from normal and hypophysectomized rats.
• Assessment of [125I]IGF-II binding to microsomal membranes and washed supernatants.
• Scatchard analysis to determine binding affinity constants.
• Cross-linking studies followed by SDS-PAGE to identify IGF binding moieties.

Main Results:

• Hypophysectomy reduced [125I]IGF-II binding to microsomal membranes but increased binding in the washed supernatant.
• Hypox rat liver supernatant exhibited higher affinity for IGF-II compared to normal rat supernatant.
• Specific IGF binding moieties (42K, 39K, 31K, 27K in normal; 42-39K doublet in hypox plasma; 39K in normal microsomal SN; 42K and 34K in hypox microsomal SN) were identified.
• Binding activity was found in Golgi-endosome fractions of hypox rat liver supernatant.

Conclusions:

• Hepatic IGF binding proteins, especially in vesicular elements, interfere with IGF-II binding to membrane receptors.
• These binding moieties may influence intracellular IGF binding and peptide biological activity.
• Hypophysectomy alters the distribution and characteristics of hepatic IGF binding proteins.