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Clinical Chemistry 47: 726-729, 2001;
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(Clinical Chemistry. 2001;47:726-729.)
© 2001 American Association for Clinical Chemistry, Inc.

Articles

Measurement of Immunoreactive Angiotensin-(1–7) Heptapeptide in Human Blood

Juerg Nussbergera,1, Dorette B. Brunner1, Juerg A. Nyfeler1, Lilly Linder1 and Hans R. Brunner1

1 Hypertension Division CHUV, CH-1011 Lausanne, Switzerland.
a Author for correspondence. Fax 41-21-314 0761; e-mail juerg.nussberger{at}chuv.hospvd.ch.

Background: The renal enzyme renin cleaves from the hepatic {alpha}2-globulin angiotensinogen angiotensin-(1–10) decapeptide [Ang-(1–10)], which is further metabolized to smaller peptides that help maintain cardiovascular homeostasis. The Ang-(1–7) heptapeptide has been reported to have several physiological effects, including natriuresis, diuresis, vasodilation, and release of vasopressin and prostaglandins.

Methods: To investigate Ang-(1–7) in clinical settings, we developed a method to measure immunoreactive (ir-) Ang-(1–7) in 2 mL of human blood and to estimate plasma concentrations by correcting for the hematocrit. A sensitive and specific antiserum against Ang-(1–7) was raised in a rabbit. Human blood was collected in the presence of an inhibitor mixture including a renin inhibitor to prevent peptide generation in vitro. Ang-(1–7) was extracted into ethanol and purified on phenylsilylsilica. The peptide was quantified by radioimmunoassay. Increasing doses of Ang-(1–7) were infused into volunteers, and plasma concentrations of the peptide were measured.

Results: The detection limit for plasma ir-Ang-(1–7) was 1 pmol/L. CVs for high and low blood concentrations were 4% and 20%, respectively, and between-assay CVs were 8% and 13%, respectively. Reference values for human plasma concentrations of ir-Ang-(1–7) were 1.0–9.5 pmol/L (median, 4.7 pmol/L) and increased linearly during infusion of increasing doses of Ang-(1–7).

Conclusions: Reliable measurement of plasma ir-Ang-(1–7) is achieved with efficient inhibition of enzymes that generate or metabolize Ang-(1–7) after blood sampling, extraction in ethanol, and purification on phenylsilylsilica, and by use of a specific antiserum.






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