Angiotensin I converting enzyme of rat intestinal and vascular surface membrane

High levels of angiotensin I converting enzyme are present in rat intestinal mucosa and in intestinal arteries. Homogenates of both tissues were subfractionated and fractions enriched in vascular plasma membrane or intestinal brush border were prepared. The preparations were identified and their purities established by marker enzyme enrichment and/or electron microscopy. Converting enzyme activity was highly enriched on both the vascular plasma membrane and the intestinal brush border. Subsequently the properties of these membrane-bound enzymes were compared. Both surface membrane-bound enzymes were highly sensitive to inhibition by captopril (SQ 14225) and teprotide (SQ 20881). Similar to converting enzyme isolated from other sources, they were also inhibited by bradykinin, angiotensin I, EDTA and o-phenanthroline. Finally, both membrane-bound enzymes were relatively resistant to activation by sonication, freezing and thawing or detergent. These results demonstrate significant similarities between surface membrane-bound converting enzyme from vascular and non-vascular sites. In addition, in view of the possible relationship of kinins and angiotensins to gastrointestinal function and blood flow, inhibition of gastrointestinal converting enzyme by captopril may affect some aspects of intestinal physiology.

Angiotensin-converting enzyme substrates hydrolyzed by fibroblasts and vascular endothelial cells

Angiotensin-converting enzyme (ACE, E.C. 3.4.15.1) activity has been documented in eight cultures of fibroblasts with the ACE substrates benzoyl-phe-ala-pro and hippuryl-his-leu. Hydrolysis of these ACE substrates by fibroblasts is inhibited by SQ-14225 and SQ-20881, specific inhibitors of ACE activity, and by EDTA. However, ACE activity in seven of eight cultures of fibroblasts tested is less than ACE activity in two cultures of vascular endothelial cells. The rats of hydrolysis of benzoyl-phe-ala-pro by fibroblasts and by endothelial cells differ at high substrate concentrations; therefore, the ACE activity in fibroblasts may be due to either a different isoenzyme of ACE of a different accessibility to substrate. Production of angiotensin II from angiotensin I is documented in cultures of vascular endothelial cells but not in cultures of fibroblasts, however, angiotensin II is further degraded by fibroblasts and not by endothelial cells.

Immunohistochemical localization of tonin in rat salivary glands and kidney

Tonin has been localized in salivary glands and kidney by the indirect immunofluorescence technique of Coons and by the unlabeled antibody technique of Sternberger. Both techniques gave identical results. Immunoreactive tonin was localized in the cytoplasm of granular convoluted tubular cells and on the apical surface of striated duct cells and collecting duct cells of the submandibular gland. In the parotid and sublingual glands, which lack granular cells, tonin was only found on the apical surface of striated duct and collecting duct cells. In the kidney, immunoreactive tonin was found only associated with cells of the distal convoluted tubules. After fixation with Bouin fluid or with ethanol, tonin was found not only on the apical surface of the cells but also in the apical and perinuclear cytoplasm. This cytoplasmic staining has been attributed to artefactual diffusion since, after fixation with formol-picric acid, the enzyme could only be localized on the apical surface of the tubular cells.

Brain angiotensin-converting enzyme activity in experimental hypertensive rats

Angiotensin-converting enzyme (ACE) activity was measured in six areas of the brain of normotensive and experimental hypertensive rats; one-clip, one-kidney (1-c, 1-k) and one-clip, two-kidney (1-c, 2-k) Goldblatt hypertensive (GH) rats. ACE activity was consistently high in the thalamus of normotensive and both 1-c, 1-k and 1-c, 2-k GH rats. However, the enzyme activity in the hypothalamus of 1-c, 2-k GH rats was significantly higher than that of normotensive rats, while there was no significant difference in the enzyme activity between normotensive and 1-c, 1-k GH rats. These results demonstrate that in 1-c, 2-k GH rats, increased ACE activity in the brain may play a central role in the hypertension.

Cells originating from sarcoid granulomas in vitro

In an attempt to obtain in vitro experimental models for sarcoidosis, the primary cultures of granuloma cells were initiated with lymph nodes from 10 sarcoidosis patients. The cells migrating from tissue explants became confluent at 2 wk of culture. These cells exhibited overall morphologic features and enzymatic activities resembling those of in vivo granuloma epithelioid cells. By light and electron microscopy, the epithelioid cell in vitro contained a clear, large nucleus with 1 or 2 prominent nucleoli. The cytoplasm was characterized by the occurrence of lysosomal dense bodies and electron-lucent vacuoles, besides many mitochondria and well-developed Golgi complexes. The cell surface exhibited many processes, mainly lamellipodia. Large amounts of angiotensin converting enzyme activity (3.9 to 50.1 nmol/min/ml) lysozyme activity (3.9 to 23.0 micrograms/ml) were demonstrated in the medium used for culture. The results indicated that the major cell population grown in these cultures is derived from the epithelioid cells in sarcoid granulomas.

[Increased concentration of angiotensin I converting enzyme in the alveolar fluid of patients with sarcoidosis]

Angiotensin converting enzyme (ACE) was assayed both in serum (SACE) and in bronchoalveolar fluid lavage (LACE) in 14 healthy controls and in 45 patients with sarcoidosis with mediastinal and pulmonary involvement. Concentration of SACE was 4466 +/- 2202 U x 100 ml-1 (mean +/- SD) in sarcoidosis and 2470 +/- 547 U x 100 ml-1 (chi +/- SD) in sarcoidosis and 2470 +/- 547 U . 100 ml-1 in controls. Concentrations of LACE were 65.2 +/- 48.4 U . 100 ml-1 and 21.1 +/- 14.7 U . 100 ml-1 respectively in sarcoidosis and in controls. These results are in favor of an intraalveolar secretion of ACE in sarcoidosis. LACE could be a better criterium than SACE for the evaluation of the pulmonary activity of sarcoidosis.

Effect of sodium intake on brain angiotensin-converting enzyme activity in spontaneously hypertensive rat

The effect of sodium intake on angiotensin-converting enzyme activity in five areas of the brain (the cerebral cortex, midbrain, striatum, thalamus and hypothalamus) was studied in normotensive, spontaneously hypertensive and stroke-prone spontaneously hypertensive rats. The enzyme activity was significantly higher in the hypothalamus than in other areas of the brain of spontaneously hypertensive rats. Sodium intake resulted in a significant rise of the enzyme activity in the midbrain of spontaneously hypertensive rats and also in the midbrain and the striatum of stroke-prone spontaneously hypertensive rats. In normotensive rats, however, there was no significant difference in the enzyme activity in any area of brain between the control and the salt-treated group. It is likely therefore that a high circulating sodium level increases angiotensin-converting enzyme content of the brain in spontaneously hypertensive rats, and it is suggested that the increased converting-enzyme activity may play a role in development of hypertension induced by sodium loading.

Angiotensin converting enzyme concentrations in the lung lavage of normal rabbits and rabbits treated with nitrogen mustard exposed to hyperoxia

Increased concentrations of angiotensin converting enzyme (ACE) were found in lung lavages from rabbits exposed to hyperoxia for 72 h and the concentrations of ACE were correlated with ratios of extravascular lung water to body weight (r = 0.69, p less than 0.05) and albumin concentrations in lung lavages (r = 0.89, p less than 0.01). In parallel studies, rabbits treated with nitrogen mustard in which granulocytopenia was maintained throughout the 72-h hyperoxic exposure period had less evidence of edematous lung injury and lower concentrations of ACE in their lung lavages than similarly treated rabbits in which granulocytopenia was not maintained. The results suggested that granulocytes contribute to acute edematous lung injury from hyperoxia and that ACE concentrations in lung lavages reflect this process.

Levels of angiotensin-converting enzyme in pleural effusion

The value of determining the angiotensin-converting enzyme (ACE) in serum has been clearly established, particularly in sarcoidosis, but is significance in pleural effusions is practically unknown. In the present study, ACE level was determined in the pleural fluid of 18 hospitalized patients along with the values for total protein, lactic acid dehydrogenase (LDH), complete and differential cell counts and cytology. The ACE level was higher in exudates than in transudates and paralleled closely the total protein level in the pleural fluid. There was no correlation between ACE and LDH levels and either WBC or RBC counts in the effusions. The ACE levels failed to discriminate between benign and malignant diseases or to correlate with any specific etiology for the effusion. There was a significant gradient between ACE levels that were higher in the serum than in the effusion of all nine patients in whom both were measured. The filtration coefficient (ratio of pleural fluid to serum concentration of a protein) of ACE was less than that of total protein and was compatible with ACE penetration in the pleural fluid by a process of diffusion.

Inhibition of rabbit tissue kininase by anti-(endo-oligopeptidase A) antibodies

Highly purified rabbit brain endo-oligopeptidase A injected into goats produced, after 60 days of immunization, antisera that specifically inhibit purified rabbit brain endo-oligopeptidase A. An immunoreactive kininase having the same specificity as rabbit brain endo-oligopeptidase A for bradykinin was detected in several rabbit tissues. The highest amount of this immunoreactive kininase was found in the 25000 g supernatant fraction (S fraction) of heart, liver, skeletal muscle, ovary, brain and testis homogenates, corresponding to 89, 86, 78, 59, 56 and 53% respectively of the whole kininase activity found in the S fraction.

Immunohistologic diagnosis of sarcoidosis. Detection of angiotensin-converting enzyme in sarcoid granulomas

Angiotensin-converting enzyme (ACE) was detected by indirect immunofluorescence examination. ACE was present in the cytoplasm of epithelioid cells in granulomas from 38 of 39 patients who had clinical sarcoidosis but not in any of 37 nonsarcoid granulomas, normal lymph nodes, or splenic controls. Intensity of staining with ACE antiserum was inversely proportional to the degree of fibrosis and was significantly less intense in fibrotic granulomas. The detection of ACE appears to be a distinct aid in establishing a definitive tissue diagnosis of sarcoidosis.

Angiotensin-converting enzyme in Crohn's disease and ulcerative colitis

The relationship between serum angiotensin-converting enzyme activity and inflammatory bowel disease was investigated in 37 patients who had Crohn's disease, 31 patients who had ulcerative colitis, and 104 control subjects. The enzyme activity tended to be depressed in Crohn's ileitis (P less than 0.05) and colitis, but not in Crohn's ileocolitis and ulcerative colitis. No increase in enzyme activity was observed in Crohn's disease ileum or colon or in ulcerative colitis colon. The granulomatous inflammation in Crohn's disease differs from that in sarcoidosis, in which striking elevation of angiotensin-converting enzyme is present in granulomatous tissue and frequently in serum.

Assessment of bleomycin lung toxicity using angiotensin-converting enzyme in pulmonary lavage

Activity of the dipeptidyl hydrolase angiotensin-converting enzyme has been observed to be altered by treatment with bleomycin. We used an animal model of bleomycin lung toxicity to study the effects on angiotensin-converting enzyme activity in various lung fractions. Serum activity of angiotensin-converting enzyme increased only 23% after a single intratracheal instillation of bleomycin. Lung tissue angiotensin-converting enzyme activity fell to 40% of control level (p < 0.05) and returned toward and eventually exceeded control values during the ensuing 6 weeks. However, angiotensin-converting enzyme activity in alveolar lavage fluid from bleomycin-treated rats was elevated 30-fold above the barely detectable levels found in control animals. Angiotensin-converting enzyme activity in lavage fluid was soluble and was not associated with the alveolar cell pellet. Maximum elevation of lavage angiotensin-converting enzyme activity occurred 3 days following bleomycin instillation. Significant transudation of serum into alveolar lavage fluid occurred in bleomycin-treated rats. Nevertheless, this phenomenon would not explain the high levels of angiotensin-converting enzyme activity found in lavage fluid. Elevated lavage angiotensin-converting enzyme levels were detected after doses of bleomycin too low to cause significant sequelae of pulmonary fibrosis. Lavage angiotensin-converting enzyme is a sensitive monitor of tissue response to bleomycin.

Angiotensin converting enzyme in the brain of spontaneously hypertensive rats

1. Angiotensin converting enzyme (ACE) was measured in homogenates of regions of rat brain using the substrate Hip-His-Leu. 2. The enzyme resembles classical ACE in its marked Cl- dependence and inhibition by both SQ 20,881 (24 micro mol/1) and EDTA (1 mmol/1). 3. Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto controls (NT-WK) were killed at 20-22 weeks of age their brains dissected into eight regions. 4. There were marked region variations of ACE with highest levels in striatum, hippocampus, cerebellum and pituitary and lower levels in hypothalamus and cerebral cortex. 5. In three brain regions ACE was significantly lower in SHR compared to NT-WK: medulla oblongata (P < 0.05), hypothalamus (P < 0.02) and cerebral cortex (P < 0.05). In the other sites the levels were not different. 6. These region-specific differences of ACE in the SHR could lead to altered production or metabolism of central neuropeptides postulated to be involved in the control of blood pressure.

Immunofluorescent detection of angiotensin-converting enzyme (ACE) in Gaucher cells

The cellular localization of the elevated angiotensin-converting enzyme (ACE) in the spleen of a patient with Gaucher's disease was examined by immunofluorescence using an antibody prepared against highly purified human lung enzyme. Intense ACE-specific cytoplasmic fluorescence was observed in Gaucher cells, but not in various controls, indicating the localization of large quantities of enzyme in these cells. These results and the demonstrated capability of mononuclear phagocytes for marked induction of this enzyme suggest the possibility that induction of active synthesis of ACE in Gaucher cells may be responsible for the elevated enzyme levels in the serum and spleen of patients with Gaucher's disease.

Lack of detection of factor VIII in sarcoidal epithelioid cells

We investigated the possibility that epithelioid cells in sarcoidosis contain abundant angiotensin-converting enzyme, because these cells are derived from endothelial cells, which normally contain the enzyme in abundance. Granulomas from 9 patients with sarcoidosis were examined for the presence of the endothelial cell marker, factor VIII, by immunofluorescence microscopy using monospecific anti-human factor VIII antibody. Strong factor VIII-specific fluorescence was detected in the endothelial cells but no fluorescence was observed in the epithelioid cells. These results do not support the origin of epithelioid cells in sarcoidosis from endothelial cells as an explanation for their abundance of angiotensin-converting enzyme.

Effects of captopril (SQ 14, 225) on the renin-angiotensin-aldosterone system in normal rats

High doses of captopril (SQ 14, 225) (120-160 mg/kg/day) were administered orally to normal rats, and the effects on the renin-angiotensin-aldosterone system were observed. Plasma angiotensin converting enzyme (ACE) activity was elevated significantly on the 3rd, 7th and 30th days of captopril administration. ACE activity in the lung and the kidney was significantly decreased on the 1st day then gradually increased, becoming significantly higher than that of controls by the 30th day. Plasma renin activity (PRA) was significantly elevated on the 1st day and remained at a high level until the 30th day. Renal renin content was found to be significantly lower on the 1st and 3rd days. Plasma aldosterone concentration was not affected by captopril treatment, whereas serum potassium concentration was found to be significantly lower on the 1st, 3rd and 30th days. It is suggested that besides its inhibitory action on ACE, captopril has a direct or indirect stimulating action on ACE production as well as on renin release.

Angiotensin-converting enzyme: II. Pulmonary endothelial cells in culture

Direct studies of the function of a given cell type often require that the cell type be obtained in pure culture. A number of different specific metabolic activities have been attributed to pulmonary endothelial cells, yet with few exceptions the conclusions were based on indirect evidence. Thus, to improve our ability to examine directly for specific metabolic activities, we began a program to obtain pulmonary endothelial cells in culture. Two methods have been developed: (1) cells can be obtained from pulmonary artery and vein of large animals (cow, pig), and (2) cells can be obtained from the microvasculature of small animals (rat, guinea pig, and rabbit). The latter technique can also be used to obtain cells from a lobe of lung from large animals and may be adaptable for use with human tissue. In the first technique, pulmonary arteries, free of blood, are filled with collagenase (0.25%, 500 units) in Puck's saline for 25 min. The collagenase mixture containing cells is removed and centrifuged. The pellet is resuspended and seeded into culture flasks. In the second method, lungs are perfused (artery to vein) with Krebs-Henseleit solution until the effluent is blood-free. Collagenase (0.25%, 500 units) is introduced, and the lungs are then perfused in the opposite direction (vein to artery) until the flow stops spontaneously (ca. 15 min). The detached cells are collected and seeded as before. The endothelial cells attach as small clumps (10-50 cells). Those flasks which contain more than 95% endothelial cells (by phase microscopy) are retained for culture and the lines are purified usng differential adherence procedures. The cells grow as monolayers with a cobblestone appearance. They contain Weibel-Palade bodies. They possess converting enzyme activity and are reactive with antibodies to converting enzyme, Factor VIII and alpha 2-macroglobulin. The cells synthesize prostaglandins and related substances. In addition, they possess ADPase and synthesize angiotensin-converting enzyme.

Angiotensin-converting enzyme: I. New strategies for assay

The disposition of converting enzyme (kininase II) on the luminal surface of pulmonary endothelial cells is well established. Further, it is known that there is a net conversion of angiotensin I into angiotensin II as blood passes through the lungs. However, little is known about modulations of converting enzyme activity that may arise through, e.g., changes in the quality of inhalants, blood flow, or blood oxygenation. There are few data on the effects of lung disease. A major barrier to studies to examine for pathophysiologic modulations of converting enzyme is that of assay. The enzyme can be measured in terms of the rate of formation of angiotensin II from a known quantity of angiotensin I. However, both peptides are biologically active, and lungs contain other enzymes capable of degrading them. We have developed a series of radiolabeled, acylated tripeptides to improve our ability to examine for changes in the net converting enzyme of intact lungs. The enzyme, a dipeptidyl carboxypeptidase, is capable of removing C-terminal dipeptides from a variety of oligopeptides. We have prepared benzoyl-Gly-Gly-Gly (I), benzoyl-Pro-Phe-Arg (II), benzoyl-Gly-His-Leu (III), benzoyl-Phe-Ala-Pro (IV), and benzoyl-Phe-His-Leu (V), each containing a (3)H-atom in the para position of the benzoyl moiety. Substrates I and III have been used previously in photometric assays of low sensitivity. II is the acylated C-terminal tripeptide of bradykinin, IV is an acylated tripeptide analog of BPP(5a) (<Glu-Lys-Trp-Ala-Pro) and V is the acylated C-terminal tripeptide of angiotensin I. These substrates can be used in vitro or in vivo to measure converting enzyme. The (3)H-labeled product is separable by partitioning between an organic solvent and acidified aqueous solution. The product is quantified by scintillation counting of the organic phase. The choice of substrate depends on the goals of the experiment: substrate I or III when wide variations in substrate concentrations are needed but high sensitivity is not; substrate IV when high sensitivity is needed.

Effect of acute lung injury on angiotensin converting enzyme in serum, lung lavage, and effusate

The administration of an acute pulmonary edemagenic dose (ip) of thiourea to rats results in an elevation of angiotensin converting enzyme (ACE) in serum, lung lavage, and pleural effusion. The increased serum ACE corresponds to a reduction in lung ACE, but it is transient, lasting between 1 and 2 h. ACE remains elevated in lung lavage and pleural effusion for at least 4 h after the administration of thiourea.

Angiotensin-converting enzyme in human prostate

The activity of angiotensin-converting enzyme in human prostate was measured by spectrophotometric method using Hippuryl-L-histidyl-L-leucine (Hip-His-Leu) as substrate. Benign hypertrophic prostate had significantly higher concentration of angiotensin-converting enzyme (1.99 +/- 0.36 (S.E.M.) units/g of tissue, n = 13) than normal prostate (0.44 +/- 0.1 units/g of tissue, n = 5) (p less than 0.01). More than 80% of the enzyme activity occurred in soluble fraction of normal and hypertrophied prostates. Human prostatic angiotensin-converting enzyme, partially purified from benign hypertrophic prostates, had an apparent molecular weight of 290,000 and pI of 4.1. Optimum pH of the enzyme with KM value of 1.0 mmol/l was 7.8 in 0.1 mmol/l borate/sodium/carbonate buffer. The enzyme was competitively inhibited by captopril (Ki, 1.8 nmol/l).

Kinins and angiotensins. Angiotensin I converting enzyme (kininase II) in endothelial cells cultured from human pulmonary arteries and veins

Human pulmonary endothelial cells were used to study the metabolism of angiotensin I and bradykinin by angiotensin I converting enzyme (kininase II; ACE). The endothelial cells cultured from pulmonary arteries and veins differed with respect to their enzyme activity and their surface structure, as viewed with scanning electron microscopy. Cells from adult pulmonary arteries had greater ACE activity than cells from either adult pulmonary veins or fetal pulmonary arteries. In addition, cells from adult pulmonary arteries exhibited more prominent surface projections than cells from veins or fetal pulmonary arteries. A brief exposure to trypsin decreased the ACE activity in cells from arteries but not in cells from veins. Possible the differences in ACE activity between these cells are related to their surface structures.

Isolation and culture of endothelial cells from the lungs of small animals

Techniques are descirbed for the isolation and culture of endothelial cells from the lungs of small animals. The cells are collected by retrograde perfusion of blood-free lungs with buffered saline containing collagenase. The cells are characterized by light microscopy, electron microscopy of thin sections and surface replicas, and by the presence of angiotensin-converting enzyme (ACE). ACE was assayed using 3H-benzoyl-Phe-Ala-Pro as substrate and was localized by indirect immunofluorescence using guinea pig endothelial cells incubated with rabbit antibodies to guinea pig lung ACE followed by goat anti-rabbit globulins conjugated to fluorescein. Thus, endothelial cultures can be established using small animals commonly employed in studies of pulmonary processing of vasoactive substances.

Chromatographic determination of angiotensin-converting enzyme and angiotensinase activity

An analytical method utilizing an automatic amino acid analyzer is described for the separation, identification, and measurement of 5 to 50 nmol of angiotensin I, angiotensin II, [Des-Phe8]angiotensin II, Phe-His-Leu, His-Leu, isoleucine, leucine, tyrosine, and phenylalanine. Aminex A-5 cation-exchange resin (0.9 x 15 cm) is sequentially eluted with three sodium citrate buffers: pH 3.25, 0.2 N; pH 4.85, 0.54 N, and pH 6.5, 0.39 N at 60 and 80 degrees C. Reaction with ninhydrin is used for detection. This chromatographic system was used to determine angiotensin-converting enzyme activity and the angiotensinase activity of rabbit brain endopeptidase B. In each assay, the unhydrolyzed substrate and both products were measured simultaneously in one step without pretreatment of the hydrolysate. Products were recovered in 1:1 molar ratios and the overall recovery of an hydrolyzed substrate of products was quantitative.

Gestational changes in pulmonary converting enzyme activity in the fetal rabbit

Changes in angiotensin-converting enzyme were measured in the lungs of fetal rabbits isolated and perfused in situ at varying ages from 22 days gestation to 7 days of age under controlled conditions of flow, pH, and temperature. Enzyme activity was assessed by infusing bradykinin or angiotensin I in Krebs-Henseleit solution and measuring residual peptide in the effluent by radioimmunoassay. The levels of substrate studied were below those required for enzyme saturation. Lungs of 22 day gestation fetuses removed only one-third of either peptide. The activity at term and in neonatal life resulted in more than 80% peptide removal. The time of the greatest rise in the percent substrate cleared occurs earlier than the time of the greatest increase in lung and body weight. The lower percentage of substrate cleared in early gestation appears to result in part from a limited surface area for enzyme activity in the primitive fetal pulmonary microvascular bed, since morphological studies with fluorescein-tagged anticonverting enzyme antibody demonstrated the presence of enzyme in the lung as early as 17 days of gestation. Electron micrographs of the pulmonary endothelial cell surface reveal that the degree of surface infolding and hence surface area increases with gestation. The higher percentage of substrate cleared in later gestation closely parallels the structural and ultrastructural development of the vascular bed. The presence of converting enzyme in the placenta by the second third of gestation and the large size of the placenta suggest that this organ may be a major locus of converting enzyme activity in the fetus.

A direct radioimmunoassay for tonin

A sensitive radioimmunoassay for the measurement of tonin is described. It is based on the use of antibodies produced in rabbits against highly purified tonin obtained from rat submaxillary gland. A radioiodinated enzyme with high specific activity was obtained by the chloramine-T method. Optimal conditions for radioimmunoprecipitation were established and the double-antibody method was used to separate bound and free tonin. The radioimmunoassay may be used to measure tonin in amounts as low as 150 pg. This radioimmunoassay was applied to the measurement of tonin in rat saliva and in homogenates of submaxillary glands. Excellent correlation was found between tonin activity measured fluorometrically and tonin concentration obtained by the radioimmunoassay.

A simple radioassay for angiotensin-converting enzyme

Angiotensin-converting enzyme can be measured by the rate of release of 3H-labelled hippurate from p-[3H]benzoylglycylglycylglycine. The product is separable from the substrate by extraction of acidified reaction mixtures with ethyl acetate. Assay results for human serum angiotensin-converting enzyme can be obtained within 1.5 h of receipt of serum samples. Within the limits tested, the assay appears to be specific. However, interference by hitherto unrecognized enzymes of abnormal sera must be ruled out.

A rapid fluorometric assay of angiotensin-converting enzyme

A rapid, simple and sensitive method is described for the fluorometric assay of angiotesin-converting enzyme using Fluorescamine. The critical factors such as optimal pH, incubation time, chloride ion, and inactivation by EDTA and 8-hydroxyquinoline were examined. The Km value for hippuryl-L-histidyl-L-leucine was 0.5 mM. This method was applied to the assay of angiotensin-converting enzyme in the rat serum and the reproducible values were obtained with a 10 mul of the rat serum.

Sarcoidosis--1977

Sarcoidosis is defined as a multisystem disorder characterised by the finding of epithelioid cell granulomas in more than one system. Diagnosis is aided by the use of the Kveim Siltzbach skin test and the development of an "in vitro" Kmif test is discussed. Despite extensive researches the causative agent(s) remains unknown. The granulomas, morphologically, on light and electron microscopy and histochemistry may be indistinguishable from those caused by known agents. Inclusion bodies are also non specific. Central necrosis is rare, and can be usually distinguished from caseation. The close relationship between the monocyte derived, epithelioid cells and lymphocytes is emphasised. Evidence is accumulating that epithelioid cells in sarcoid type granulomas are primarily synthesising rather than phagocytic cells. The products are considered to be mucoglycoproteins and may have both local and systemic actions. Locally it is suggested that the products may be lymphokines which react with associated thymic derived (T) lymphocytes and mononuclear cells and thus play a role in perpetuating the granulomas. Epithelioid cells may also be a source of circulating T lymphocyte function depressants. It has further been suggested that epitheloid cells are the source of the raised angiotensin converting enzyme found in sarcoid sera. Study of epithelioid cell granulomas in sarcoidosis, despite the disappointing lack of evidence of a causative sarcoid agent(s), is thus of considerable interest in furthering knowledge of many diseases characterised by these curious cellular foci.

The angiotensin I converting enzyme

The angiotensin I converting enzyme (kininase II; peptidyl dipeptidase; EC3.4.15.1) has a dual function: it converts angiotensin I to angiotensin II and it inactivates bradykinin. Lung, kidney, guinea pig plasma and testicles are among the richest sources of the enzyme. Vascular endothelial cells and bursh borders of renal proximal tubular cells contain high concentrations of the enzyme. The availability of synthetic peptide inhibitors was a great help in establishing the function of converting enzyme in normal and pathological conditions.