Biomedical subjects

V G Manolopoulos

Publications and source records attributed to V G Manolopoulos.

17 recordsLinked to original sources

PubMed2005

Pharmacogenomics education: International Society of Pharmacogenomics recommendations for medical, pharmaceutical, and health schools deans of education.

Pharmacogenomics would be instrumental for the realization of personalized medicine in coming decades. Efforts are evident to clarify the potential bioethical, societal, and legal implications of key pharmacogenomics-based technologies projected to be soon introduced into the core practice of medicine. In sharp contrast, a lack of sufficient attention to educational aspects of pharmacogenomics, both for professionals and for society at large, is evident. In order to contribute to this discussion, a 'Pharmacogenomics Education Forum' was held on October 2, 2004 during the 3rd Annual Meeting of the International Society of Pharmacogenomics (ISP) at Santorini, Greece. The participants, members of the ISP Pharmacogenomics Education Forum, after deliberate discussions, proposed a document of 'Background Statement' and 'Recommendations and Call for Action' addressed to Deans of Education at Medical, Pharmaceutical, and Health Schools globally. This document has been considered by the education committee of the International Society of Pharmacogenomics and the result is presented here. We hope that this call would be listened to, and soon followed by beneficial action, ultimately leading to enhanced implementation of personalized medicine into core medical education and practice.

Curriculum↗

PubMed2001

Regulation of extracellular matrix remodeling and MMP-2 activation in cultured rat adrenal medullary endothelial cells.

We previously reported that short term exposure of cultured rat adrenal medullary endothelial cells (RAMEC) to thrombin enhances the subendothelial deposition of extracellular matrix (ECM) proteins fibronectin, laminin, and collagen types I (C-I) and IV (C-IV) (Papadimitriou et at., 1997). In this work, we extended our previous studies on factors that affect ECM protein deposition to include agents that activate or inhibit some of the most common intracellular signals such as cAMP, protein kinase C (PKC) and calcium. Furthemore, we investigated the possible link between the observed alterations in ECM protein deposition and the secretion of matrix metalloproteinase-2 (MMP-2). Forskolin (adenylyl cyclase activator) caused a dose-dependent increase in the deposition of all four ECM proteins studied. Isoproterenol (beta-adrenergic receptor agonist) and the membrane-permeant cAMP analogue dibutyryl-cAMP, significantly increased the deposited amounts of ECM proteins at low concentrations, and this increase was reversed at higher concentrations of both agents. All these agents had the opposite effect on MMP-2 secretion, increasing it at doses where they decreased ECM protein deposition and vice-versa. However, elevation of cAMP by the phosphodiesterase inhibitor IBMX had no effect neither on the deposited amounts of any of the ECM proteins studied nor on MMP-2 secretion. Activation of PKC by phorbol ester (PMA) resulted in a decrease in ECM protein deposition and an increase in MMP-2 secretion. Finally, chelation of intercellular calcium with BAPTA-AM resulted in an increased ECM deposition and a decrease in MMP-2 secretion, Our results show a complex pattern of regulation of ECM protein deposition by cAMP-mobilizing agents, and also indicate an inverse correlation between ECM protein deposition and secretion of MMP-2. The concerted regulation of both these processes is essential in the formation of new blood vessels and for the integrity of the vascular wall.

Adrenal Medulla↗

PubMed2001

Regulation of extracellular matrix remodeling and MMP-2 activation in cultured rat adrenal medullary endothelial cells.

We previously reported that short-term exposure of cultured rat adrenal medullary endothelial cells (RAMEC) to thrombin enhances the subendothelial deposition of extracellular matrix (ECM) proteins fibronectin, laminin, and collagen types I (C-I) and IV (C-IV) (Papadimitriou et al. 1997). In this work, we extended our previous studies on factors that effect ECM protein deposition to include agents that activate or inhibit some of the most common intracellular signals such as cAMP, protein kinase C (PKC), and calcium. Furthermore, we investigated the possible link between the observed alterations in ECM protein deposition and the secretion of matrix metalloproteinase-2 (MMP-2). Forskolin (adenylyl cyclase activator) caused a dose-dependent increase in the deposition of all four ECM proteins studied. Isoproterenol beta-adrenergic receptor agonist) and the membrane permeant cAMP analogue dibutyryl-cAMP significantly increased the deposited amounts of ECM proteins at low concentrations, and this increase was reversed at higher concentrations of both agents. All these agents had the opposite effect on MMP-2 secretion, increasing it at doses where they decreased ECM protein deposition and vice versa. However, elevation of cAMP by the phosphodiesterase inhibitor IBMX had no effect either on the deposited amounts of any of the ECM proteins studied or on MMP-2 secretion. Activation of PKC by phorbol ester (PMA) resulted in a decrease in ECM protein deposition and an increase in MMP-2 secretion. Finally, chelation of intercellular calcium with BAPTA-AM resulted in an increased ECM deposition and a decrease in MMP-2 secretion. Our results show a complex pattern of regulation of ECM protein deposition by cAMP-mobilizing agents and also indicate an inverse correlation between ECM protein deposition and secretion of MMP-2. The concerted regulation of both of these processes is essential in the formation of new blood vessels, and for the integrity of the vascular wall.

Adrenal Medulla↗

PubMed2000

Inhibition of angiogenesis by blockers of volume-regulated anion channels.

Osmotic cell swelling activates an outwardly rectifying Cl(-) current in endothelial cells that is mediated by volume-regulated anion channels (VRACs). In the past, we have shown that serum-induced proliferation of endothelial cells is arrested in the presence of compounds that potently block the endothelial VRACs. Here we report on the effects of four chemically distinct VRAC blockers [5-nitro-2-(3-phenylpropylamino)benzoic acid] (NPPB), mibefradil, tamoxifen, and clomiphene-on several models of experimental angiogenesis. Mibefradil (20 microM), NPPB (100 microM), tamoxifen (20 microM), and clomiphene (20 microM) inhibited tube formation by rat microvascular endothelial cells plated on matrigel by 42.9 +/- 8.8%, 25.3 +/- 10.4%, 32.2 +/- 4.5%, and 20 +/- 5.8%, respectively (p < 0.05). Additionally, NPPB (50-100 microM) and mibefradil (10-30 microM) significantly inhibited bFGF (10 ng/ml) + TNFalpha (2.5 ng/ml)-stimulated microvessel formation by human microvascular endothelial cells plated on fibrin by 30-70%. Furthermore, NPPB, mibefradil, and clomiphene concentration dependently inhibited spontaneous microvessel formation in the rat aorta-ring assay and vessel development in the chick chorioallantoic membrane assay. These results suggest that VRAC blockers are potent inhibitors of angiogenesis and thus might serve as therapeutic tools in tumor growth and other angiogenesis-dependent diseases.

Allantois↗

PubMed1999

Characterisation of explanted endothelial cells from mouse aorta: electrophysiology and Ca2+ signalling.

We describe here the isolation and primary culture of endothelial cells from mouse aorta ("primary explant technique"). These cells provide an excellent model for functional studies in transgenic mice. The primary explant method delivers cells that grow out from small pieces of mouse aorta placed on Matrigel enriched with endothelial growth factors. Cells can be studied on the Matrigel after removing the pieces of aorta or after passages by using dispase and reseeding the cells on gelatine-coated cover-slips. Cells on Matrigel or from the first and second passages were characterised using the combined patch-clamp and fura-2 fluorescence methods. Cells had a mean membrane resting potential of -19+/-3 mV (n=21), a membrane capacitance of 49+/-5 pF (n=37) and a resting cytosolic free [Ca2+] ([Ca2+]i) of 103+/-8 nM (n=30). Adenosine 5'-triphosphate (ATP), acetylcholine and bradykinin, but not histamine, induced fast release of intracellular Ca2+ followed by a sustained rise in [Ca2+]i. Oscillations in [Ca2+]i were observed at lower agonist concentrations. In nearly all cells (93%, n=30), these agonists activated charybdotoxin-sensitive, Ca2+-activated K+ channels and induced hyperpolarisation. In 84% of the cells (n=32), an increase in [Ca2+]i also activated strongly outwards-rectifying Cl- channels. These activated slowly at positive potentials and inactivated rapidly at negative potentials. Increasing [Ca2+]i to 1 microM activated a non-selective cation channel in 86% of the cells (n=28). Each tested cell responded to a challenge with hypotonic solution by activating a Cl- current that was modestly outwards rectifying and inactivated at positive potentials. This current is similar to the well-described swelling-activated current through volume-regulated anion channels (VRAC) in endothelial cells. However, its activation is slower, its inactivation faster and the current density lower than in cultured endothelial cells. It is concluded that the primary explant technique provides a reliable cell model for studying mouse vascular endothelial cell function.

Acetylcholine↗

PubMed1999

Expression patterns of sarco/endoplasmic reticulum Ca(2+)-ATPase and inositol 1,4,5-trisphosphate receptor isoforms in vascular endothelial cells.

Expression patterns of sarcoplasmic/endoplasmic-reticulum Ca(2+)-ATPase (SERCA) and inositol 1,4,5-trisphosphate receptor (IP3R) isoforms were studied in endothelial cells at the mRNA level by ratio RT-PCR technique and subsequent restriction-enzyme analysis. Three types of cells have been used in the present study: rat adrenal medulla microvascular endothelial cells (RAMEC), rat aortic endothelial cells (RAEC), and human umbilical vein endothelial cells (HUVEC). Our data show the presence of multiple SERCA and IP3R isoforms in each type of endothelial cells. Freshly isolated HUVEC were an exception in this respect since they contained only SERCA3 without SERCA2b messengers. The expression patterns changed upon cell proliferation: SERCA3 and IP3R-1 messengers decreased, while IP3R-3 increased with culturing. Upon cell differentiation, induced by culturing the cells on Matrigel, the expression pattern of the IP3R changed even further in all endothelial cell types: IP3R-1 was reduced in all three cell kinds, while IP3R-3 raised significantly in RAEC and RAMEC. In HUVEC the expression of SERCA returned, upon differentiation, to the levels observed in the freshly isolated cells. Thus, the plasticity of expression of various SERCA and IP3R isoforms shows that possibly different Ca2+ pools may play distinct roles in cell proliferation and differentiation.

Adrenal Medulla↗

PubMed1997

The thrombin receptor in adrenal medullary microvascular endothelial cells is negatively coupled to adenylyl cyclase through a Gi protein.

The effects of thrombin on adenylyl cyclase activity were examined in rat adrenal medullary microvascular endothelial cells (RAMEC). Confluent RAMEC monolayers were stimulated for 5 min with cAMP-generating agents in the absence and presence of thrombin, and intracellular cAMP was measured with a radioligand binding assay. Thrombin (0.001-0.25 U/ml) dose-dependently inhibited IBMX-, isoproterenol- and forskolin-stimulated cAMP accumulation. A peptide agonist of the thrombin receptor, gamma-thrombin, and the serine proteases trypsin and plasmin, also inhibited agonist-stimulated cAMP levels, while proteolytically inactive PPACK- or DIP-alpha-thrombins were without effect. Moreover, the thrombin inhibitor hirudin abolished the inhibitory effect of thrombin but not of the peptide agonist. These results suggest that the inhibitory action of thrombin on cAMP accumulation is mediated by a proteolytically-activated thrombin receptor. The inhibitor of G(i)-proteins pertussis toxin abolished the inhibitory effect of thrombin on isoproterenol- or IBMX-stimulated cAMP production, while the phorbol ester PMA partly impaired it. The protein kinase C inhibitors staurosporine or H7 and the intracellular Ca2+ chelator BAPTA-AM were without effect. Collectively, our data suggest that the thrombin receptor in RAMEC is negatively coupled to adenylyl cyclase through a pertussis toxin-sensitive G(i)-protein.

Adenylate Cyclase Toxin↗

PubMed1997

Hypotonicity and thrombin activate taurine efflux in BC3H1 and C2C12 myoblasts that is down regulated during differentiation.

The efflux of organic osmolytes such as taurine is an important mechanism by which cells regulate their volume. The effects of hypotonicity and thrombin on taurine efflux were studied in BC3H1 and C2C12 cells, two mouse myoblastic cell lines that can be induced to differentiate with serum deprivation. In proliferating cultures of both cell types preloaded with [3H]taurine, exposure to 27% hypotonicity activated a 10- to 20-fold increase in [3H]taurine efflux (Jtau). This effect was blocked by the C1- channel inhibitors NPPB and flufenamic acid. Thrombin and the thrombin receptor agonist SFLLRN also activated Jtau that was abolished by NPPB and flufenamic acid. Together, hypotonicity and thrombin synergistically activated Jtau. In differentiated myocytes, the effect of thrombin was abolished, while that of hypotonicity was significantly reduced. These results suggest that (i) hypotonicity and thrombin activate taurine-permeable anion channels in BC3H1 and C2C12 cells, and (ii) these anion channels may be involved in cell proliferation.

Animals↗

PubMed1997

Thrombin modulates vectorial secretion of extracellular matrix proteins in cultured endothelial cells.

We have identified a novel cellular action of thrombin on cultured rat adrenal medullary endothelial cells (RAMEC). Five-minute incubation of RAMEC with physiological concentrations of thrombin (<1 U/ml) caused within 3 h an increase in the basolateral deposition of the extracellular matrix (ECM) proteins fibronectin, laminin, and collagens IV and I, concomitant with a corresponding decrease in the apical release of these proteins into the medium. This shift in vectorial secretion of ECM proteins, quantitated with enzyme-linked immunoassays, was time dependent. Maximal stimulation of ECM protein deposition was observed after incubation of cells with thrombin for 5-15 min. Prolonged exposure (>1 h) to thrombin resulted in loss of proteins from the ECM. Thrombin-stimulated ECM protein deposition exhibited a bell-shaped dose dependence, peaking for all proteins at 0.25 U/ml of thrombin, and was independent of de novo mRNA or protein synthesis. Maximal amounts of deposited proteins increased between 2.5-fold (fibronectin) and 4-fold (collagen I) over baseline values. Similar results were obtained with thrombin receptor agonist peptide (TRAP), proteolytically active gamma-thrombin, and, to a lesser extent, other serine proteases such as trypsin and plasmin. A scrambled TRAP, proteolytically inactive PPACK-thrombin, DIP-thrombin, and type IV collagenase were ineffective. Together, these results suggest that the thrombin effects are mediated by proteolytic activation of the thrombin receptor. Possible involvement of the phospholipase C-signaling pathway in thrombin-mediated ECM protein deposition was also investigated. Inhibition or downregulation of protein kinase C (PKC) and chelation of intracellular or extracellular Ca2+ did not suppress, but rather enhanced, basal and thrombin-stimulated ECM protein deposition. Quantitative differences in augmentation of basolateral deposition by these treatments suggest differential regulatory pathways for individual ECM proteins. Our data indicate that, in cultured RAMEC, short-term activation of the thrombin receptor causes an increase in amounts of deposited ECM protein by a cellular signaling pathway that is independent of PKC activation and/or elevation of intracellular Ca2+.

Adrenal Medulla↗

PubMed1997

Swelling-activated efflux of taurine and other organic osmolytes in endothelial cells.

We used a combined biochemical, pharmacological, and electrophysiological approach to study the effects of hyposmotic swelling on organic osmolyte efflux in endothelial cells (EC). In [3H]taurine-loaded monolayers of calf pulmonary artery EC (CPAEC), hyposmolality activated time- and dose-dependent effluxes of [3H]taurine. Swelling-activated [3H]taurine efflux (Jtau swell)in CPAEC was inhibited by the anion channel blockers tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), fenamates, and also quinine (in a pH-dependent manner), ATP, and the phospholipase A2 inhibitor 4-bromophenacyl bromide. In contrast, Jtau swell was partly or totally insensitive to bumetanide, forskolin, phorbol 12-myristate 13-acetate, and staurosporine. Swelling also activated myo-[3H]inositol efflux that was blocked by tamoxifen, NPPB, DIDS, and niflumic acid. Moreover, the cellular content of taurine and other amino acids was significantly reduced in osmotically activated CPAEC. Finally, in whole cell patch-clamp experiments, taurine, glycine, aspartate, and glutamate exhibited significant permeability for swelling-activated anion channels. In conclusion, hyposmotic swelling activates efflux of taurine and other organic osmolytes in EC. In addition, our results suggest that anion channels may provide a pathway for swelling-activated efflux of organic osmolytes in EC.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1996

Tissue factor expression is differentially modulated by cyclic mechanical strain in various human endothelial cells.

Many of the hemostatic properties of endothelium are modulated by chemical and mechanical stimuli. The nature of such endothelial cell (EC) responses often depends upon the anatomical origin of the cells within the vascular tree. In the present study, we used a chromogenic assay to investigate the effect of cyclic strain or tumor necrosis factor alpha (TNF alpha), or both, on tissue factor (TF) activity in human EC derived from umbilical veins (HUVEC), aortae (HAEC), and dermal microvessels (HMVEC). Basal TF activities were low in all three cell types. Incubation for 5 h with (10 ng/ml) TNF alpha resulted in quantitatively diverse elevation of TF activity in all three EC types. Exposure to cyclic strain for 5 h induced significant elevation of TF activity only in HMVEC and HAEC. Concomitant application of cyclic strain and TNF alpha resulted in synergistic elevation of TF expression only in HMVEC. Pharmacologic elevation of cyclic AMP (cAMP) levels and inhibition of protein kinase C (PKC) levels inhibited TNF alpha-induced TF expression in all EC types. However, none of these treatments affected the stimulatory action of cyclic strain in HMVEC. Thus, we have shown that TNF alpha differentially increases TF activity in human EC of various origins, that cyclic strain variably modulates TF activity in human EC, and that both PKC and cAMP mediate TNF alpha-induced TF activity, whereas cyclic strain acts independently of these pathways. These results show differential modulation of the procoagulant potential of diverse human endothelial cells in vitro by hemodynamic stimuli.

Cells, Cultured↗

PubMed1995

Adenylyl cyclase isoforms are differentially expressed in primary cultures of endothelial cells and whole tissue homogenates from various rat tissues.

The expression of five adenylyl cyclase isoforms (types II-VI) was studied with reverse transcription-polymerase chain reaction in whole tissue homogenates and in primary cultures of endothelial cells isolated from rat aorta, vena cava, heart, lung, adipose fat, brain, and adrenal medulla. It was found that: i) all endothelial cell types express all adenylyl cyclase isoforms studied, albeit at different levels depending on the tissue origin of the cells, and ii) the adenylyl cyclase isoform profile of isolated endothelial cells differs from that of homogenates of their parent tissues. Our data show a unique endothelial cell type specificity of AC isoform expression, which varies from that of the whole organ. These results support the idea that one of the factors mediating differential regulation of the cAMP cascade in EC in various locations within the vascular tree might be quantitative differences in the levels of AC isoforms expressed in each EC type.

Adenylyl Cyclases↗

PubMed1995

Regulation of the adenylyl cyclase signaling system in various types of cultured endothelial cells.

We studied the effects of modulators of the adenylyl cyclase pathway on the accumulation of cAMP in endothelial cells isolated from bovine aortas, pig pulmonary arteries, human umbilical veins, and human subcutaneous adipose microvessels. In addition to quantitative differences in the basal levels, cAMP stimulation in different endothelial cell types varied in sensitivity and magnitude in response to both the direct adenylyl cyclase activator forskolin and the beta-adrenergic receptor agonist isoproterenol. Furthermore, the ubiquitous phosphodiesterase inhibitor IBMX differentially enhanced both the basal and the stimulated cAMP levels in the various cell types. Histamine caused an elevation of cAMP only in bovine aortic endothelial cells and in human umbilical vein endothelial cells. Treatment of the cells with cholera and pertussis toxins, which uniquely affect G-protein subunits, resulted in divergent elevation of cAMP in the various cells. Thus, in each cell type, a distinct profile of regulation of the cAMP levels was found. Our results suggest that the adenylyl cyclase signaling system in various types of endothelial cells can be differentially regulated at the levels of receptors, G-proteins, adenylyl cyclase, and phosphodiesterase.

1-Methyl-3-isobutylxanthine↗

PubMed1993

Cyclic strain and forskolin differentially induce cAMP production in phenotypically diverse endothelial cells.

The effects of cyclic strain and forskolin on cAMP production were studied in 4 endothelial cell types. Basal cAMP levels varied among the various types. Cyclic strain induced an increase in cAMP levels in endothelial cells isolated from bovine aortae, pig pulmonary arteries and human adipose microvessels, but not in endothelial cells isolated from human umbilical veins. 100 microM forskolin induced a differential increase in cAMP which ranged from 5-fold in pig pulmonary artery endothelial cells to 50-fold in human microvascular endothelial cells. Forskolin and cyclic strain, when applied to the cells concomitantly, had no additional effects on cAMP levels. However, when forskolin was applied 5 min after initiation of cyclic strain, a synergistic elevation of cAMP was observed in human umbilical vein endothelial cells. This action of forskolin was not mimicked by isoproterenol (10 microM). We suggest that the cAMP signalling system of phenotypically diverse endothelial cells is differentially regulated by cyclic strain and forskolin and that these differences might contribute to endothelial cell phenotypic diversity.

Animals↗

PubMed1991

Inositol phosphates formed in rat aorta after alpha 1-adrenoceptor stimulation are inhibited by forskolin.

Rat aortic smooth muscle rings without endothelial cells were subjected to alpha 1-adrenoceptor stimulation. We measured the contractile state of the smooth muscle cells and the formation of inositol phosphates (InsPs) on receptor stimulation. Using different extracellular calcium-containing solutions (2.5 mM, 0.1 mM and Ca(2+)-free) enabled us to discriminate three contractile phases after noradrenaline (10(-5) M) stimulation: an initial fast contraction (15 s) and a fast and slow component of the sustained contraction, which was established 10 min after stimulation. Under normal calcium conditions in the presence of 10 mM LiCl the formation of Ins(1,4,5)P3 was increased predominantly after stimulation, while the formation of Ins(1,3,4)P3, Ins(1,3,4,6)P4, Ins(1,3,4,5)P4, Ins(3,4,5,6)P4 and InsP5/InsP6 was also stimulated. The cAMP-inducing agent forskolin (0.5 microM) induced a relaxation of the basal tone and increased the level of the InsP4 isomers. The noradrenaline-induced contractile responses as well as the formation of InsP fractions mentioned were inhibited by forskolin. Further an increase in the formation of phosphatidylinositol bisphosphate was observed. It is concluded that in rat aorta InsPs and in particular Ins(1,4,5)P3 is involved in the different contractile phases caused by alpha 1-adrenoceptor stimulation. The relaxation induced by forskolin under these circumstances could be explained by an interaction of forskolin, most likely via the formation of cAMP, with InsPs formation at the level of phospholipase C activation.

Adrenergic alpha-Agonists↗

PubMed1991

Human plasma-derived material with clonidine displacing substance (CDS)-like properties contracts the isolated rat aorta.

1. The biological activity of a plasma-derived, clonidine displacing substance (CDS)-like material was tested on isolated rat aortic rings and compared to that of clonidine, an imidazoline with alpha 2-adrenoceptor agonist properties. 2. The CDS-like material was partially purified from expired human blood. This product inhibited in a dose-dependent manner the binding of [3H]-clonidine to rat brain membranes with a ki of 0.87 +/- 0.4 u ml-1, without affecting the binding of the alpha 1-antagonist, [3H]-WB4101. 3. When the CDS-like material (0.14-6 u ml-1) was applied to the bathing medium of isolated rat aortic rings, it caused dose-dependent contractions with an EC50 of 1.0 +/- 0.18 u ml-1. Clonidine also dose-dependently contracted rat aortic rings (EC50, 1.1 +/- 0.24 x 10(-7) M). The maximal tension developed in response to clonidine, however, was higher (1.37 +/- 0.15 g) compared to that developed in response to the CDS-like material (0.92 +/- 0.12 g). 4. Contractions induced by both CDS-like material and clonidine were antagonized by 5 x 10(-7) M rauwolscine, an alpha 2-adrenoceptor antagonist. Prazosin, an alpha 1-adrenoceptor antagonist, at 10(-8) M, greatly reduced contractions caused by clonidine while leaving those caused by CDS-like material unaffected. 5. The CDS-like material failed to alter the tension of intact or endothelium-denuded rat aortic rings which had been precontracted with methoxamine. Clonidine on the other hand, caused dose-dependent relaxations in intact, though not in denuded, precontracted rat aortic rings.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗

PubMed1989

Angiotensin converting enzyme activity is present in the endothelium-denuded aorta.

Angiotensin converting enzyme activity was measured in intact aortic rings utilizing the synthetic tripeptide [3H]-benzoyl-Phe-Ala-Pro as the substrate. Intact aortic rings possessed angiotensin converting enzyme activity which was blocked by captopril. Enzyme activity was reduced by approximately 30% after removal of the endothelium by chemical or mechanical methods. The remaining activity was also captopril-sensitive. These results suggest that in addition to endothelium, angiotensin converting enzyme activity is present in other vascular cells and may contribute to the metabolism of angiotensin I generated within the vessel wall.

Acetylcholine↗