Measurement of angiotensin II: use of two injectors to minimize HPLC shadowing

Specific and non-specific measurements of tissue angiotensin II cascade members

Although angiotensin II (ANG II) has been the focal regulatory peptide of the renin-angiotensin system, its proteolytic fragments have recently been demonstrated to have biological effects. Conventional measurement of angiotensins involves radioimmunoassay (RIA), which is a sensitive binding technique capable of measuring low physiological concentrations. However, ANG II antibody cross-reacts with ANG II and its fragments (ANG II cascade), rendering RIA measurement alone to be a non-specific measure of immunoreactive ANG II (ir-ANG II). On the other hand, high-performance liquid chromatography (HPLC) is capable of separating immunoreactive ANG II cascade members, but may not be sensitive enough to detect these low peptide concentrations often present in biological samples. Consequently, a reverse-phase HPLC method, with triethylammoniun formate as an ion-pair reagent, was developed to separate ANG II and its fragments, ANG III, ANG IV and ANG V. This HPLC separation was applied to extracts from normal canine hearts and ANG II cascade immunoreactive fractions were collected. Collected fractions were quantified by RIA, with the use of separate standard curves. The isocratic HPLC separation of ANG II, ANG III, ANG IV and ANG V was achieved in less than 5 min with adjacent peaks having baseline resolution. Measured cardiac left ventricle ANG III, ANG IV and ANG V concentrations (mean+/-SD) were 5.3+/-2.2,4.0+/-1.0 and 3.1+/-1.0 fmol/g (n=9), respectively. There was a significant difference (P=0.003, n=9) between left ventricular immunoreactive ANG II and 'true' ANG II, corrected for recovery rates of 86.2+/-22.5 and 53.5+/-16.2 fmol/g, respectively. We conclude that the combination of HPLC with RIA ensures the specific measurement of the ANG II cascade family members while non-chromatographic processing of tissue renders ANG II measurement non-specific. In addition, the use of triethylammonium formate as mobile phase additive is superior in the HPLC separation of the angiotensins.

Simultaneous separation of angiotensin and endothelin peptide families by high-performance liquid chromatography: application to the specific radioimmunoassay measurement of angiotensin II or endothelin-1 from tissue

Currently available measurements of endogenous angiotensin II (ANG II) and endothelin-1 (ET-1) concentrations by radioimmunoassay (RIA) lack specificity to ANG II or ET-1. ANG II and ET-1 antibodies cross-react with immuno-reactive angiotensin and endothelin family members, respectively. We have therefore developed an ion-pair reversed-phase high-performance liquid chromatography (HPLC) for simultaneously separating angiotensin and endothelin peptides and enhancing RIA specificity in the measurement of ANG II and ET-1. The developed HPLC separation was applied to canine myocardium extracts; ANG II or ET-1 fractions were collected and quantified by RIA. Elution times for both peptide families, ANG I, ANG II, ANG III, ANG IV, ANG II(4-8), bET-1, ET-1, ET-2 and ET-3 were within 25 min. In normal canine myocardium from the right atrium, right ventricle, left atrium and left ventricle, ANG II concentrations were 39+/-11, 28+/-21, 31+/-11 and 21+/-8 fmol/g and ET-1 concentrations were 43+/-16, 42+/-19, 55+/-21 and 57+/-34 fmol/g (mean+/-SD, N=7), respectively. The combination of HPLC with RIA renders the measurement of ANG II or ET-1 specific and convenient, and saves time. This HPLC separation may be applied to the specific measurement of other immuno-reactive angiotensin and endothelin peptides.