Letter to the editor: Angiotensin quantification by mass spectrometry

TO THE EDITOR:
With great interest, we have read Mark Chappell’s (4) comprehensive overview on molecular components of the renin-angiotensin system (RAS). It focused on the analytical methods that can be used to determine the activity or concentration of these molecules, with special emphasis on RIA and ELISA.
We fully agree that the sampling procedure is critical to obtain reliable data on angiotensin levels, independent of the method that is used for detection. Obtaining blood samples for angiotensin quantification requires the immediate addition of an efficient protease inhibitor cocktail ensuring efficient stabilization of angiotensin metabolites by instantly blocking all proteases involved in their metabolism. The sampling time has to be kept as short as possible, and an immediate and efficient mixture of the blood sample and the inhibitor cocktail is essential to avoid artifacts, which is particularly challenging when collecting blood samples from mice. The importance of the sampling time is often underestimated and is likely the cause of unexpected shifts of peptide metabolite patterns despite the use of appropriate protease inhibitor cocktails.
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