High-performance liquid chromatography for the separation of angiotensin and its metabolites in human plasma and sweat

A reversed-phase high-performance liquid chromatography (HPLC) method with gradient elution for the separation of angiotensin peptides is described. The highly reproducible method allows the base-line separation of angiotensin peptides with UV detection at 225 nm. This chromatographic methodology in combination with radioimmunoassay (RIA) is used for the characterization of angiotensin peptides in human plasma and sweat.

Release of immunoreactive angiotensin II from neuronal cultures: adrenergic influences

The effects of adrenergic drugs on the release of immunoreactive angiotensin II (ANG II-ir) from brain cells in culture were examined. In neuronal cultures, basal release of Ang II-ir was 43.65 +/- 7.44 pg/5-min incubation period (n = 14 experiments; 52 individual determinations), and in astrocytic glial cultures, it was 21.76 +/- 5.7 pg (n = 8 experiments; 24 individual determinations) when cells were exposed to buffer alone. Incubation of neuronal cultures with the alpha 2-adrenergic antagonist yohimbine (0.1-50 microM, 5 min) caused concentration-dependent increases in ANG II-ir release above basal levels. Analysis of the released material by high-pressure liquid chromatography revealed that authentic ANG II was present. No increase in the release of ANG II-ir was seen from glial cells. Experiments using neuronal cultures revealed that the yohimbine-induced release of ANG II-ir may be secondary to increased norepinephrine (NE) release. Incubation of neuronal cultures with NE (10 nM-50 microM) caused concentration-dependent increases in the release of ANG II-ir. This effect of NE was not inhibited by the alpha 1-adrenergic blocker prazosin. However, a weaker release of ANG II-ir from neuronal cultures was stimulated by the beta-adrenergic agonist isoproterenol at 100 microM. These data show that ANG II-ir can be released from neuronal but not glial cell cultures by adrenergic receptor-mediated mechanisms.

Metabolism of angiotensin peptides by neuronal and glial cultures from rat brain

The degradation pattern and rate of [Ile5]-Angiotensin (Ang) I, II, and III were studied in neuron-enriched and glia-enriched cells in primary cultures from rat brain. Metabolites were separated by HPLC, and their identities were evaluated by comparison of their retention times with those of synthetic Ang peptide fragments and by analysis of their amino acid composition. Major metabolites were identified as des-Asp1-[Ile5]-Ang I, des-Asp1-[Ile5]-Ang II, [Ile5]-Ang II (3-8) hexapeptide, [Ile5]-Ang II (4-8) pentapeptide, and [Ile5]-Ang II (5-8) tetrapeptide. Glia-enriched cells degraded [Ile5]-Ang I and [Ile5]-Ang III significantly faster than neuron-enriched cells, whereas no difference between the two types of cells was found in the degradation rate of [Ile5]-Ang II. Although the half-lives of [Ile5]-Ang I and [Ile5]-Ang III in neuron-enriched cells from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were not significantly different, neuron-enriched cultures from WKY rats metabolized [Ile5]-Ang II about 2.6 times faster than neuron-enriched cells derived from SHR.

Chromatographic methods for characterization of angiotensin in brain tissue

Ang II antiserum with high sensitivity and specificity was produced. The native Ang II antiserum was purified by affinity chromatography on Affi-Gel 102 with covalently coupled [Ile5]Ang II, and purified Ang II antiserum was covalently coupled to Affi-Gel 10. The column with the covalently coupled Ang II antiserum was used for the specific enrichment of Ang II from brain extracts. The efficiency and usefulness of affinity chromatography for the purification of Ang II from biological sources were tested with 125I-labeled, 3H-labeled, and synthetic [Ile5]Ang II added to rat brains prior to extraction. In addition, the methodology was used for the purification of endogenous Ang II from pig brain. The described three-step procedure for the isolation and purification of Ang II including extraction, affinity chromatography, and HPLC is rapid and highly specific with high loading capacity. We have applied the method to the peptide Ang II in brain, but the methodology may also be used in general for the rapid purification of other neuropeptides. A combination of HPLC with specific radioimmunoassays for Ang I and Ang II was utilized to demonstrate that rat brain cells in culture devoid of the influence of the peripheral RAS were able to synthesize radioactively labeled Ang I and Ang II after incubation with [3H]isoleucine. And, finally, an HPLC system capable of separating Ang I, Ang II, and its metabolites was used to obtain insight into the degradation pattern of angiotensin peptides in the brain. Aminopeptidases appear to be the major angiotensin-degrading enzymes, and endopeptidases do not appear to be involved.

Biosynthesis of angiotensinogen and angiotensins by brain cells in primary culture

This study focuses on the ability of primary rat brain cells in culture to synthesize angiotensinogen, angiotensin I, and angiotensin II. HPLC in combination with radioimmunoassay was used to characterize these compounds. Following incubation with 3H-labeled isoleucine, radioactively labeled angiotensinogen with an approximate molecular weight of 25,000 was identified in both glial and neuronal cells. Other molecular weight forms of angiotensinogen with molecular weights of about 300 and 160,000 were present in both cell types. In addition to angiotensinogen, radioactively labeled angiotensin I and angiotensin II were also synthesized by neuronal and glial cells. These results suggest that glial and neuronal cells can synthesize angiotensinogen, angiotensin I, and angiotensin II in a similar manner shown for the peripheral renin angiotensin system.

Measurement and characterization of angiotensin peptides in plasma

We report a method for the extraction of angiotensin peptides from plasma with a mixture of acetone, 1 mol/L HCl, and water (40/1/5 by vol). The method is highly reproducible for the measurement of angiotensin I and angiotensin II in small sample volumes, with analytical recoveries of about 80% for both peptides. We investigated the influence of sample handling and found a standard procedure for blood collection, plasma preparation, and extraction was essential. The method was used to measure angiotensin I and II in rat and human plasma. In rat plasma, the mean (+/- SEM) concentrations of angiotensin I and angiotensin II were determined to be 67 (+/- 8) and 14 (+/- 1) pmol/L (n = 10), respectively. Neither angiotensin I nor angiotensin II was detectable 24 h after bilateral nephrectomy. Acute oral administration of the converting-enzyme inhibitor ramipril caused a significant increase of angiotensin I from 85 (+/- 6) to 257 (+/- 33) pmol/L (n = 10; P less than 0.001) and a significant decrease of angiotensin II from 12 (+/- 1) to 7 (+/- 0.4) pmol/L in rat plasma (n = 9; P less than 0.001). In human plasma, angiotensin I and angiotensin II values of 21 (+/- 1) and 6.6 (+/- 0.5) pmol/L (n = 10) were found. A single oral dose of the diuretic furosemide increased angiotensin I significantly from 21 (+/- 1) to 32 (+/- 1.7) pmol/L (n = 5); P less than 0.001), whereas angiotensin II remained unchanged, 6.6 (+/- 0.5) vs 6.4 (+/- 0.4) pmol/L (n = 5). Extracted peptides could be identified as [IIe5]-angiotensin I and [IIe5]-angiotensin II by HPLC in combination with specific radioimmunoassays for angiotensin I and angiotensin II.

Measurement and characterization of angiotensin peptides in plasma

We report a method for the extraction of angiotensin peptides from plasma with a mixture of acetone, 1 mol/L HCl, and water (40/1/5 by vol). The method is highly reproducible for the measurement of angiotensin I and angiotensin II in small sample volumes, with analytical recoveries of about 80% for both peptides. We investigated the influence of sample handling and found a standard procedure for blood collection, plasma preparation, and extraction was essential. The method was used to measure angiotensin I and II in rat and human plasma. In rat plasma, the mean (+/- SEM) concentrations of angiotensin I and angiotensin II were determined to be 67 (+/- 8) and 14 (+/- 1) pmol/L (n = 10), respectively. Neither angiotensin I nor angiotensin II was detectable 24 h after bilateral nephrectomy. Acute oral administration of the converting-enzyme inhibitor ramipril caused a significant increase of angiotensin I from 85 (+/- 6) to 257 (+/- 33) pmol/L (n = 10; P less than 0.001) and a significant decrease of angiotensin II from 12 (+/- 1) to 7 (+/- 0.4) pmol/L in rat plasma (n = 9; P less than 0.001). In human plasma, angiotensin I and angiotensin II values of 21 (+/- 1) and 6.6 (+/- 0.5) pmol/L (n = 10) were found. A single oral dose of the diuretic furosemide increased angiotensin I significantly from 21 (+/- 1) to 32 (+/- 1.7) pmol/L (n = 5); P less than 0.001), whereas angiotensin II remained unchanged, 6.6 (+/- 0.5) vs 6.4 (+/- 0.4) pmol/L (n = 5). Extracted peptides could be identified as [IIe5]-angiotensin I and [IIe5]-angiotensin II by HPLC in combination with specific radioimmunoassays for angiotensin I and angiotensin II.

Immunocytochemical and biochemical characterization of angiotensin I and II in cultured neuronal and glial cells from rat brain

Neuronal and glial cells cultured from neonatal rat brains showed staining for both angiotensin I and II using the peroxidase-antiperoxidase method. In glial cell extracts of normotensive Wistar-Kyoto rats, the concentrations of angiotensin I and II were 12.47 +/- 2.71 (n = 4) and 66.73 +/- 13.28 fmol/mg protein (n = 4). Angiotensin I and II found in neuronal cell extracts of normotensive Wistar-Kyoto rats were 11.29 +/- 2.99 (n = 4) and 60.25 +/- 12.77 fmol/mg protein (n = 4). No significant difference was found in the concentration of angiotensin I and II in both cell types from the same rat strain. Angiotensin I concentrations of 16.83 +/- 3.43 fmol/mg protein (n = 5) determined in neuronal cell extracts derived from spontaneously hypertensive rats did not differ significantly from those found in neuronal cell extracts of Wistar-Kyoto rats. However, neuronal cell extracts from spontaneously hypertensive rats revealed values of 25.19 +/- 4.31 fmol angiotensin II/mg protein (n = 4). This was significantly different (p less than 0.05) and represented a 58% reduction in the angiotensin II levels in neuronal cells from spontaneously hypertensive rats compared to Wistar-Kyoto rat cultures. Angiotensin I and II measured in the growth medium containing 10% plasma-derived horse serum was below the detection limit of both radioimmunoassays. No difference in the angiotensin I and II levels was found in cells kept in serum-free medium. The angiotensin I and II immunoreactive material determined in the cell extracts could be characterized on reversed-phase high pressure liquid chromatography as (Ile5)-angiotensin I and II. (Ile5)-angiotensin III was not detectable.

Presence of renin in primary neuronal and glial cells from rat brain

Immunocytochemical and biochemical techniques have been utilized in the present study to characterize renin in brain cell cultures. With the use of renin-specific antibody, positive renin staining was seen in neuronal and in astrocytic glial cells using the peroxidase-antiperoxidase method. Renin concentration was pH-dependent with highest concentrations at 5.5, decreasing from pH 6.0 to 6.5. At pH 7.4 no renin was detectable in either glial or neuronal cells. The contribution of cathepsin D to the measured renin was about 10% at pH 5.5; 7% at pH 6.0 and 3% at pH 6.5. Comparison of glial with neuronal cells from WKY rats revealed significantly elevated renin at pH 5.5 in glial cells. No difference was seen between glial and neuronal renin levels in WKY rats at pH 6.0 and 6.5. At pH 5.5 and 6.0 renin was significantly increased in neuronal cells of SHR compared to WKY, whereas at pH 6.5 no difference was observed. The renin concentration in cells kept for 2 days in serum-free medium did not differ from those measured in cells kept in serum-containing medium. The generated peptide was identified as [Ile5]Angiotensin I on reversed-phase HPLC.

[Value and rank of diagnostic laboratory parameters in cardiovascular diseases. Results of multivariant and discriminant analyses of the Berlin EBMO-Cor population study]

Based on present clinical-chemical parameters a representative population were studied; importance and order of rank of 10 data chosen from a total data pool are determined by means of multivariant and discriminant analysis. As a result the validity of characters with and without apriori probabilities for 5 pairs of classes (persons suffering from a heart disease in comparison to healthy persons divided in sexes and overall, as well as examination of separate sexes for healthy persons and those suffering from a heart disease) are examined (alpha less than or equal to 0.05). This calculation tested the importance of the parameters hemoglobin and creatinine in being different in males and females. To diagnose persons suffering from a heart disease (X-ray-morphologically defined suspects of heart and vessel diseases) from healthy persons, the optimized number of characteristics were determined in cholesterol, erythrocyte sedimentation rate, ASAT, blood glucose (independent of sex). By means of these results it is possible to identify persons suffering from a heart disease from healthy persons and to call for illustrative laboratory examinations using already mentioned parameters and the function of discriminance W = p sigma i = 1 ai X Xi. The determination of sensitivity and specification yielded a value of up to 98 per cent resp. 94 per cent depending on whether with or without apriori probabilities. This enables use to be modified to suit different purposes.

Isolation and purification of angiotensin II using affinity and high-pressure liquid chromatography

Peptides have been found in a variety of tissues including brain. To purify the peptide angiotensin II, a three-step method for the isolation and purification has been developed using extraction, affinity chromatography, and high-pressure liquid chromatography. Angiotensin II antiserum purified by affinity chromatography was covalently coupled to Affi-gel 10 (Affi-gel 10-AB). The efficiency and usefulness of this column for the purification of angiotensin II from biological sources were tested with 125I- and 3H-labeled (Ile5)-angiotensin II added to rat brains prior to extraction. After extraction, the recoveries for both peptides were 74 and 75%, respectively. Recovery after the purification on Affi-gel 10-AB was 84 and 82%. Thirty-two percent of the radioactivity was not retained and 50% of the radioactivity could be eluted with 0.1 M Na citrate buffer containing 1 M NaCl using a stepwise pH gradient. Characterization by HPLC of the unretained radioactivity from the Affi-gel 10-AB column showed one peak for [125I]angiotensin II, coeluting with the [125I]angiotensin II standard and two minor peaks. Only 30% of unretained [3H]angiotensin II could be identified as intact [3H]angiotensin II on HPLC. Both [125I]angiotensin II and [3H]angiotensin II elutable at pH 5.0 and 4.0 on Affi-gel 10-AB could be demonstrated as highly purified [125I]angiotensin II and [3H]angiotensin II on HPLC with a purity of more than 90%. On HPLC, the recovery was 81% for [125I]angiotensin II and 99% for [3H]angiotensin II. The recovery for the entire three-step procedure was about 60%. The loading capacity of the Affi-gel 10-AB column for (Ile5)-angiotensin II was 550 ng.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinins in cerebrospinal fluid: reduced concentration in spontaneously hypertensive rats

Rat cerebrospinal fluid contains peptides which displace radiolabeled bradykinin from its specific antibodies. Two peptides which showed the same retention time as kallidin and bradykinin in a reverse phase high pressure liquid chromatography system were detected in cerebrospinal fluid of rats. The concentration of radioimmunologically detected kinins in the cerebrospinal fluid of spontaneously hypertensive rats of the Okamoto strain was lower than that of the Wistar Kyoto control rats.