Summary
The availability of a sensitive and highly specific rabbit antiserum and the development
of a peptide-extraction method employing glass beads permitted the evolution of a
rapid reliable radioimmunoassay that measures the sum of the concentration of angiotensin
II and its active metabolite, angiotensin III. At a dilution of 1:32,000 the antiserum
is capable of measuring 1 fmol (1 pg) of angiotensin II. Cross reactivities of this
antiserum, taking angiotensin II as 1.0, are: angiotensin III, 0.75; angiotensin-(3-8)
hexapeptide, 0.11; angiotensin I, 0.006; angiotensin-(1-14) tetradecapeptide, 0.0001.
The recovery of angiotensin II added to hormone-free plasma was 73 ± 2% [mean ± standard
deviation (SD), n = 20]. When 0.9 ml of plasma was extracted, the minimal concentration
of angiotensin II and III that could be quantified was 4 fmol/ml. When larger volumes
of plasma were extracted, sensitivity was enhanced. Plasma blanks were zero. Intraassay
variability was 7.6% SD and interassay variability was 11.7% SD. Angiotensin II and
III concentration in venous plasma of normal volunteers on an ad libitum diet was
15 ± 8 fmol/ml (mean ± SD, range < 4 to 35 fmol/ml). The plasma of a patient with
primary aldosteronism had an unmeasurable value (< 4 fmol/ml). Posture, converting
enzyme inhibition, and renal artery stenosis resulted in expected changes of angiotensin
concentration.
Key-Words:
Angiotensin II
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Peptide-Extraction
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Radioimmunoassay
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Angiotensin III
