'Dynorphin' in plasma: enzymatic artifact and authentic immunoreactivity.

Area of Science:

• Neuroendocrinology
• Peptide Hormone Research

Background:

• The opioid peptide dynorphin (DYN) is present in vasopressinergic neurons and adrenal medulla, suggesting potential plasma secretion.
• Accurate measurement of plasma DYN is crucial for understanding its physiological roles.

Purpose of the Study:

• To develop a sensitive radioimmunoassay for quantifying dynorphin (DYN) in human plasma.
• To investigate the presence and characteristics of DYN-like immunoreactivity (irDYN) in human circulation.

Main Methods:

• Development of a radioimmunoassay for DYN.
• Plasma extraction using various methods including leached silica glass (Vycor) and Sep-Pak C18 cartridges.
• Investigation of artifactual immunoreactivity due to enzymatic degradation.
• Immunoaffinity extraction coupled with gel filtration chromatography.

Main Results:

• Unextracted plasma or plasma extracted with Vycor showed artifactual irDYN due to tracer degradation.
• Sep-Pak C18 extraction from acidified plasma did not detect irDYN.
• Extraction of non-acidified plasma using immunoaffinity chromatography revealed a single peak of irDYN with a molecular size similar to DYN.

Conclusions:

• A small amount of a DYN-like peptide circulates in human plasma.
• This circulating peptide is not identical to porcine DYN(1-17).
• Careful extraction methods are essential to accurately measure DYN and similar peptides in plasma, avoiding enzymatic artifacts.