In vivo processing of LVV‐hemorphin‐7 in rat brain and blood utilizing microdialysis combined with electrospray mass spectrometry

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Abstract
In vivo microdialysis in combination with liquid chromatography/electrospray time‐of‐flight mass spectrometry was used to study the processing of LVV‐hemorphin‐7, an endogenous decapeptide with opioid activity, in rat brain and blood. A microdialysis probe (flow rate 0.4 μL/min) was used to both introduce LVV‐hemorphin‐7 into the striatum of the brain (1.0 pmol/μL) or the venous blood (10 pmol/μL) and to collect the metabolic products. LVV‐hemorphin‐7 was extracellularly metabolized in the striatum to form C‐terminal fragments 2–10, 3–10, 4–10, 5–10, 6–10, 7–10, and N‐terminal fragments 1–9, 1–8, 1–6. Infusion of the aminopeptidase inhibitor amastatin (1.0 pmol/μL) into the striatum, together with LVV‐hemorphin‐7, decreased the processing of LVV‐hemorphin‐7 to form C‐terminal fragments 2–10, 3–10, 4–10, but increased the relative levels of fragment 5–10 and N‐terminal fragments 1–9, 1–8 and 1–6. The major metabolic product from LVV‐hemorphin‐7 in the striatum was the C‐terminal fragment 5–10, which may be processed by an endopeptidase not sensitive to amastatin. The LVV‐hemorphin‐7 infusion to the venous blood produced the C‐terminal fragments 2–10, 3–10, 4–10, and 5–10, N‐terminal fragment 1–9, and internal fragments 4–7 and 4–9. It is concluded that the combination of microdialysis and electrospray mass spectrometry provides a powerful tool for the study of extracellular metabolism and kinetic processes of complex reaction systems in vivo. Copyright © 2003 John Wiley & Sons, Ltd.

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