The human liver growth hormone receptor

Area of Science:

• Endocrinology
• Cell Biology
• Biochemistry

Background:

• Human livers are crucial for metabolic regulation.
• Understanding hormone receptor distribution is key to comprehending cellular responses.
• Growth hormone (GH) and insulin play vital roles in liver function.

Purpose of the Study:

• To characterize the binding sites for human growth hormone (hGH) and insulin in human liver tissue.
• To determine the distribution and affinity of these hormone receptors.
• To investigate potential intracellular localization of hGH receptors.

Main Methods:

• Human liver tissue was obtained and fractionated using differential centrifugation.
• Radioligand binding assays with [125I]hGH and insulin were performed.
• Receptor affinity and capacity were quantified.
• Cross-linking studies identified receptor molecular weights.
• Hormone binding patterns in cellular fractions (nuclear, microsomal, plasma membrane) were analyzed.

Main Results:

• Specific binding of [125I]hGH was observed with high affinity (2.0 x 10^9 M-1) and variable capacity.
• hGH receptor binding sites were found in both plasma membrane and intracellular compartments (microsomes and nuclear fractions).
• Insulin binding was consistent across all livers and primarily localized to the plasma membrane, with some binding to nuclear and microsomal elements.
• Cross-linking studies suggested an hGH receptor molecular weight of approximately 103,000 Da.

Conclusions:

• Human liver possesses specific binding sites for hGH, with significant presence in intracellular compartments beyond the plasma membrane.
• Insulin receptors are predominantly located on the plasma membrane of human liver cells.
• The distribution of hGH and insulin receptors suggests distinct cellular mechanisms for their action in the liver.