Measurement of immunoreactive angiotensin-(1-7) heptapeptide in human blood.
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.
Hypertension Division CHUV, CH-1011 Lausanne, Switzerland. juerg.nussberger@chuv.hospvd.ch
J
J
Nussberger
D B
DB
Brunner
J A
JA
Nyfeler
L
L
Linder
H R
HR
Brunner
D000328:Adult; D000803:Angiotensin I / Q000097:blood*; D006801:Humans; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood*; D011863:Radioimmunoassay; D012016:Reference Values; D015203:Reproducibility of Results
D010446:Peptide Fragments; D000803:Angiotensin I; C118790:angiotensin I (1-7)