Showing papers on "Angiogenesis published in 1988"

Vasculogenesis and angiogenesis in embryonic-stem-cell-derived embryoid bodies

Abstract: Embryonic stem cells (ESC) have been established previously from the inner cell mass cells of mouse blastocysts. In suspension culture, they spontaneously differentiate to blood-island-containing cystic embryoid bodies (CEB). The development of blood vessels from in situ differentiating endothelial cells of blood islands, a process which we call vasculogenesis, was induced by injecting ESC into the peritoneal cavity of syngeneic mice. In the peritoneum, fusion of blood islands and formation of an in vivo-like primary capillary plexus occurred. Transplantation of ESC and ESC-derived complex and cystic embryoid bodies (ESC-CEB) onto the quail chorioallantoic membrane (CAM) induced an angiogenic response, which was directed by nonyolk sac endoderm structures. Neither yolk sac endoderm from ESC-CEB nor normal mouse yolk sac tissue induced angiogenesis on the quail CAM. Extracts from ESC-CEB stimulated the proliferation of capillary endothelial cells in vitro. Mitogenic activity increase during in vitro culture and differentiation of ESC. Almost all growth factor activity was associated with the cells. The ESC-CEB derived endothelial cell growth factor bound to heparin-sepharose. The identification of acidic fibroblast growth factor (FGF)in heparin-sepharose-purified material was accomplished by immunoblot experiments involving antibodies against acidic and basic FGF. We conclude that vasculogenesis, the development of blood vessels from in situ differentiating endothelial cells, and angiogenesis, the sprouting of capillaries from preexisting vessels are very early events during embryogenesis which can be studied using ESC differentiating in vitro. Our results suggest that vasculogenesis and angiogenesis are differently regulated.

Phenotypic modulation of endothelial cells by transforming growth factor-beta depends upon the composition and organization of the extracellular matrix.

Abstract: Transforming growth factor beta (TGF-beta) is angiogenic in vivo. In vitro, endothelial cell proliferation is inhibited by TGF-beta. We have correlated this inhibitory effect with an increase in cellular fibronectin synthesis and deposition in a two-dimensional culture system using specific matrix coatings. The inhibitory effect was mimicked by addition of soluble fibronectin to cultures. In contrast, TGF-beta was found to elicit the formation of tube-like structures (mimicking angiogenesis) when microvascular endothelial cells were grown in three-dimensional collagen gels. In this culture system TGF-beta elicited rapid extensive formation of complex, branching, tube-like structures, while cell proliferation was not inhibited. These data confirm and support the hypothesis that TGF-beta is angiogenic and may exert some of its effects through modulation of matrix synthesis and are consistent with the hypothesis that the organization of the extracellular environment influences cellular responses to this "panregulin."

Tumor necrosis factor suppresses transcription of the thrombomodulin gene in endothelial cells.

Abstract: Tumor necrosis factor (TNF) dramatically alters the levels of various surface components of the blood vessel wall, such as blood coagulation enzyme receptors, leukocyte-adhesive receptors, and class 1 major histocompatibility complex antigens, which may have relevance to its effects in septic shock, angiogenesis, and tumor growth. However, the precise mechanism by which the cytokine is able to accomplish this remodeling of the endothelial cell surface has not been defined. We have demonstrated that exposure of bovine and human endothelial cells to TNF leads to suppression of the functional cell surface thrombin receptor, thrombomodulin (TM), and TM mRNA of virtually identical magnitude. The cytokine has no significant effect on the stability of TM mRNA or endothelial receptor turnover. Nuclear run-on studies reveal that the treatment of endothelial cells with TNF for short periods reduces TM gene transcription to as little as 3% of control values and that this inhibition does not require new protein synthesis.

Basic fibroblast growth factor fused to a signal peptide transforms cells.

Abstract: Basic fibroblast growth factor (bFGF) is a potent growth and angiogenic factor that is found in abundance in tissues such as brain, hypothalamus, kidney and cartilage1,2. Despite this copious production of bFGF, most of these tissues are not undergoing either active growth or angiogenesis, suggesting that bFGF activity must be regulated so as to prevent autostimulation of cell growth. In cultured cells, bFGF is associated mainly with cells and basement membranes and is not released into the medium3,4. Prevention of release could be a mechanism for regulation of bFGF activity and may be a consequence of the apparent absence of a secretory-signal sequence in the bFGF protein5. Here we investigate whether this regulation can be overridden through the forced secretion of bFGF. Such secretion might provide the bFGF access to its receptor and in turn lead to autocrine transformation of the cell. We report that bFGF, as specified by a recombinant plasmid, is itself unable to induce such transformation, but acquires this ability after fusion with a secretory-signal sequence. The resulting transformants undergo unusual morphological alteration and display tumorigenicity.

Angiogenic properties of Kaposi's sarcoma-derived cells after long-term culture in vitro

Abstract: Cells derived from lung biopsies and pleural effusions from AIDS patients with Kaposi's sarcoma (KS) of the lungs were established in long-term culture with the aid of conditioned medium from HTLV-II-transformed T cells (HTLV-II CM). These AIDS-KS cells were similar to the so-called spindle cells in KS lesions and had some of their features. They produced factors that supported their own growth (autocrine) and the growth of other cells (paracrine), including umbilical vein endothelium and fibroblasts. That the AIDS-KS cells also expressed potent angiogenic activity was demonstrated by the chorioallantoic membrane assay and by subcutaneous inoculation of AIDS-KS cells into nude mice, which resulted in the development of angiogenic lesions composed of mouse cells and showing histological features similar to those of human KS lesions. These data suggest that AIDS-associated KS and possibly other types of KS may be initiated by signals that induce the growth of particular cells (spindle cells of lymphatic or vascular origin) and the expression of autocrine and paracrine activities.

Differential effects of laminin, intact type IV collagen, and specific domains of type IV collagen on endothelial cell adhesion and migration.

Abstract: Laminin and type IV collagen were compared for the ability to promote aortic endothelial cell adhesion and directed migration in vitro. Substratum-adsorbed IV promoted aortic endothelial cell adhesion in a concentration dependent fashion attaining a maximum level 141-fold greater than controls within 30 min. Aortic endothelial cell adhesion to type IV collagen was not inhibited by high levels (10(-3) M) of arginyl-glycyl-aspartyl-serine. In contrast, adhesion of aortic endothelial cells on laminin was slower, attaining only 53% of the adhesion observed on type IV collagen by 90 min. Type IV collagen when added to the lower well of a Boyden chamber stimulated the directional migration of aortic endothelial cells in a concentration dependent manner with a maximal response 6.9-fold over control levels, whereas aortic endothelial cells did not migrate in response to laminin at any concentration (.01-2.0 X 10(-7) M). Triple helix-rich fragments of type IV collagen were nearly as active as intact type IV collagen in stimulating both adhesion and migration whereas the carboxy terminal globular domain was less active at promoting adhesion (36% of the adhesion promoted by intact type IV collagen) or migration. Importantly, aortic endothelial cells also migrate to substratum adsorbed gradients of type IV collagen suggesting that the mechanism of migration is haptotactic in nature. These results demonstrate that the aortic endothelial cell adhesion and migration is preferentially promoted by type IV collagen compared with laminin, and has a complex molecular basis which may be important in angiogenesis and large vessel repair.

Transforming growth factor-beta: possible roles in carcinogenesis.

Abstract: TGF-beta is the prototype of a large family of multifunctional regulatory proteins. The principal sources of the peptide, platelets and bone, suggest that it plays a role in healing and remodeling processes. In vitro, TGF-beta is chemotactic for monocytes and fibroblasts and can greatly enhance accumulation of extracellular matrix components by fibroblasts. Its ability to stimulate the formation of granulation tissue locally and the demonstration of specific time- and tissue-dependent expression in embryogenesis suggest that similar mechanisms are operative in vivo. By analogy to its effects in wound healing and embryogenesis, it is proposed that TGF-beta, secreted by tumour cells, can augment tumour growth indirectly by effects on the stromal elements. These effects include suppression of the immune response, and enhancement of both angiogenesis and formation of connective tissue. Many tumour cells have escaped from direct growth inhibitory effects of TGF-beta by a variety of mechanisms including inability to activate the latent form of the peptide, loss of cellular receptors for TGF-beta, and loss of functional intracellular signal transduction pathways.

Endothelial cell response to pulsed electromagnetic fields: Stimulation of growth rate and angiogenesis in vitro

Abstract: The effects of pulsed electromagnetic fields on the repopulation rate of denuded regions of endothelial cell monolayers and on endothelial cell reorganization into complex vessellike structures was monitored in vitro by using human umbilical vein and bovine aortic endothelial cells. A small (20–40%) but statistically significant enhancement in growth rate of partially denuded endothelial cell monolayers as determined by tritiated thymidine incorporation was observed in the presence of pulsed electromagnetic fields. Morphologically, endothelial cells entering the denuded regions were observed to be elongated, often connecting end to end to form a mycelial or “sprouting” pattern when exposed to pulsed electromagnetic fields. This was in contrast to cells outside of the field which had a more cuboidal morphology. Complete disruption of the endothelial cell monolayer by passaging the cells with EDTA trypsin resulted in reorganization of some of the cells into three-dimensional vessellike structures after as little as 5–8 hours in the presence of the pulsed electromagnetic field. This reorganization occurred in the presence of heparin, endothelial cell growth factor, and a competent fibronectin matrix. Vas-cularization for comparable cultures outside of the field did not occur during the time-course of the experiments. Discrete stages of neovascularization were observed in the presence of the field that were qualitatively similar to stages of angiogenesis observed in vivo.

Endothelial cells synthesize basic fibroblast growth factor and transforming growth factor beta.

Abstract: Endothelial cells, including human umbilical vein endothelial cells (HUVEC), bovine aortic endothelial cells (BAEC), and bovine capillary endothelial cells (BCEC) in culture synthesize basic fibroblast growth factor (bFGF) and transforming growth factor type beta (TGF-beta). Basic FGF was cell-associated and synthesis was demonstrated by (i) the presence of bFGF mRNA species, (ii) binding to heparin-Sepharose and elution at 1.5 M NaCl, (iii) cross-reactivity with anti-bFGF antibodies when analyzed by electrophoretic blotting, and (iv) biological activity. Basic FGF was found in cell lysates at 2.3 ng/10(6) cells in HUVEC, 2.0 ng/10(6) cells in BCEC, and 13 ng/10(6) cells in BAEC. TGF-beta was secreted into media, and synthesis was demonstrated by (i) presence of TGF-beta mRNA species, (ii) cross-reactivity with anti-TGF-beta antibodies when analyzed by immunoprecipitation, (iii) competitive binding with authentic human platelet-derived TGF-beta that was blocked by TGF-beta specific blocking antibodies, and (iv) inhibition of [3H]TdR incorporation in CCl-64 cells. TGF-beta was secreted in an inactive form and required acid activation for detection. HUVEC synthesized 2.0 ng TGF-beta/10(6) cells per 12 hr; BCEC, 3.5 ng; and BAEC, 3.5 ng. HUVEC proliferation was not affected by treatment with exogenous TGF-beta, while BCEC proliferation was decreased by treatment with TGF-beta. Vascular endothelium is thus a source for these two potent multifunctional regulatory molecules, both of which may affect the growth of endothelium and neighboring fibroblasts, smooth muscle cells and white blood cells. The activation or release of these factors by endothelium may be a precipitating event in important cellular processes such as wound healing, organogenesis, and angiogenesis.

Neovascularisation and its role in the osteoarthritic process.

Abstract: In osteoarthritis angiogenesis is involved in the reinitiation of cartilage growth and mineralisation. A number of heparin binding protein growth factors have been proposed as angiogenic factors, but none of them is specific for microvessel cells. Another factor which is specific for microvessel cells, is of low molecular weight and non-profit has been called endothelial cell stimulating angiogenic factor (ESAF). ESAF has been found in significantly increased amounts in sera and synovial fluids of osteoarthritic patients and dogs. In addition to its angiogenic activity ESAF is able to activate neutral prometalloproteinases and to reactive the active enzyme-inhibitor complex. The implication of these observations in the pathogenesis of osteoarthritis is discussed.

Peptides with laminin activity

Abstract: Peptides with laminin activity are provided as follows: tyrosine-isoleucine-glycine-serine-arginine; proline-aspartine-serine-glycine-arginine; and cysteine -aspartate-proline-glycine-tyrosine-isoleucine-glycine-serine-arginine. These peptides block angiogenesis, alter the formation of capillary structures by endothelial cells, prevent the formation of excess blood vessels in tissues, and inhibit in vivo tumor cell colonization of tissues.

Angiogenin activates endothelial cell phospholipase C.

Abstract: Low concentrations of angiogenin activate the inositol-specific phospholipase C of cultured pulmonary artery, umbilical vein, and capillary endothelial cells, promoting a transient increase in the intracellular levels of 1,2-diacylglycerol and inositol trisphosphate. The response is strongly dose dependent with a maximum in the ng/ml concentration range and, for some cell lines, a marked decrease at concentrations greater than 1 ng/ml; e.g., arterial endothelial cells respond weakly to angiogenin concentrations comparable to that in normal human plasma (approximately equal to 400 ng/ml). Chemical modification of the active site of angiogenin or inhibition with placental ribonuclease inhibitor abolishes its activation of endothelial cell phospholipase C; this correlates with the concomitant loss of both intrinsic ribonucleolytic and angiogenic activity. The response to low concentrations of angiogenin is consistent with its potency of inducing vascularization in classical angiogenesis assays. In vivo, endothelial cells are exposed to concentrations of angiogenin higher than that required to elicit a cellular response; it seems likely, therefore, that expression of a surface receptor or some other process must be rate limiting in the cellular response.

Venular endothelial cells from bovine heart.

Abstract: Coronary venular endothelial cells were isolated by a bead-perfusion technique that allowed the selection of endothelial cells from venules of a specific size. Culture conditions for the microvascular cells were established. Cells grew well in supplemented Dulbecco's modified Eagle's medium. The effect of various substrata on the proliferation of the venular endothelial cells was determined. Matrigel, gelatin, and fibronectin supported high levels of proliferation. Cell shape was correlated with ability of the substratum to support cell proliferation. Cells exhibiting a broad, flattened morphology achieved high levels of proliferation. The formation of vessel meshworks by the coronary venular endothelial cells provides an in vitro model for the study of coronary angiogenesis. Confluent monolayers of these cells can be utilized to examine mechanisms of water and protein transport across coronary venules.

Endothelial cell growth factors in embryonic and adult chick brain are related to human acidic fibroblast growth factor.

Abstract: We have investigated the nature of endothelial cell growth factors in 14-day embryonic and adult chick brain extracts. Mitogenic activity was isolated by a combination of cation-exchange, heparin-Sepharose affinity, and reverse-phase HPLC. Two major mitogenic fractions eluted from heparin-Sepharose at 0.8-1.3 M and 1.5-2 M. Biologically active proteins eluting at 0.8-1.3 M NaCl, after purification to homogeneity from embryonic and adult brain, were found to possess the same amino-terminal sequence as human acidic fibroblast growth factor (aFGF). The notion that the isolated mitogens represent chick aFGF is further supported by the findings that their affinity for heparin and their retention behavior in highly resolutive HPLC are indistinguishable from those of genuine aFGF. Mitogenic activities eluting at 1.5-2 M NaCl were also present in embryonic and adult brain, but in quantities insufficient for preliminary characterization. The high specific mitogenic activity for endothelial cells, high affinity for heparin and cross-reactivity with antibodies against bovine basic FGF (bFGF) suggest a relationship of those materials with basic FGF. Our data also suggest that the sequence of aFGF is highly conserved among vertebrates. While angiogenesis occurs predominantly in the embryonic brain, the absence of notable differences in the contents of the potent angiogenic factors aFGF and bFGF in embryonic versus adult chick brain is interesting.

Rate of basement membrane biosynthesis as an index to angiogenesis.

Abstract: A method was developed for assessing collagenous protein biosynthesis from [U-14C]proline in relation to angiogenesis in the chick chorioallantoic membrane (CAM). The rate of collagenous protein biosynthesis both in vitro and in vivo was maximum between days 8 and 11 of chick embryo development. This was the stage of maximum angiogenesis as shown by morphological evaluation of the vascular density. At day 10 the rate of collagenous protein biosynthesis was 11-fold higher than that of day 15, when angiogenesis had reached a plateau. The collagenous protein formed by CAM co-elutes on SDS-agarose chromatography with the collagenous component of [3H]-acetylated-basement membrane (BM) from bovine lens capsule. 8,9-dihydroxy-7-methyl-benzo[b]quinolizinium bromide (GPA1734), which was shown previously to be a specific inhibitor of BM collagen biosynthesis, caused about 80% reduction in collagenous protein synthesis by CAM. These results indicate that most of the collagenous protein synthesized by CAM was BM collagen and this can be used as a biochemical index of angiogenesis.

Induction of angiogenesis in vitro by vanadate, an inhibitor of phosphotyrosine phosphatases

Abstract: We have previously shown that capillary endothelial cells grown on the surface of three-dimensional collagen gels can be induced to invade the underlying fibrillar matrix and to form capillary-like tubular structures in response to tumor-promoting phorbol esters or the angiogenic agent fibroblast growth factor (FGF). Since both phorbol esters and FGF stimulate phosphorylation of tyrosine residues, we treated endothelial cells with vanadate, an inhibitor of phosphotyrosine-specific phosphatases, to determine whether this agent could induce the expression of an angiogenic phenotype in these cells. We show here that vanadate stimulates endothelial cells to invade collagen matrices and to organize into characteristic tubules resembling those induced by FGF or phorbol esters. We have further observed that vanadate concomitantly stimulates endothelial cells to produce plasminogen activators (PAs), proteolytic enzymes which are induced by phorbol esters and FGF, and which have been implicated in the neovascular response; this stimulation can be accounted for by an increase in the levels of urokinase-type PA and tissue type PA mRNA. These results suggest a role for tyrosine phosphorylation in the regulation of the angiogenic phenotype in capillary endothelial cells.

The role of mast cells in wound healing.

Abstract: Mast cells are known to participate in three phases of wound healing: the inflammatory reaction, angiogenesis and extracellular-matrix reabsorption. The inflammatory reaction is mediated by released histamine and arachidonic acid metabolites. Compound 48/80 and disodium-cromoglycate are both able to increase skin breaking strength shortly after wounding. Under light and electron microscopy we found that small, granule-poor, irregular mast cells (MLMC) accumulate in the wound. This suggests that the small MLMC (mucosal-like mast cells) migrate into the skin during wound healing, and that both CTMC (connective-tissue mast cells) and MLMC are involved in tissue repair. Moreover, there is some evidence that mast cells participate in angiogenesis, since heparin is able to stimulate endothelial-cell migration and proliferation in vitro, and protamine to inhibit these processes and also angiogenesis in vivo. When the effect of protamine on wound breaking strength was examined, we encountered a decrease which was not prevented by heparin administration. Further studies are needed to demonstrate that protamine is specifically involved in inhibiting heparin-mediated angiogenesis in wounded tissue. Finally, mast cells may play a role in the extracellular matrix remodelling, on the basis of in-vitro experiments (but there are still no in-vivo data).

Inhibition of basement membrane biosynthesis prevents angiogenesis.

Abstract: GPA1734, an inhibitor of BM collagen biosynthesis, was investigated in the CAM model system for its effect on angiogenesis. Evaluation of angiogenesis was performed by placing a thin plastic coverslip inscribed with concentric circles on the CAM and counting the number of vessels intercepting the circles. The rate of BM collagen biosynthesis was monitored using [U-14C] proline incorporation into CAM proteins and determining the collagenase-digestible protein fraction. A marked depression in the vascular density was observed in the CAM area under a plastic disc containing GPA1734 as compared to control discs placed on the CAM about 1 cm apart from days 9 to 12 of incubation. A concomitant decrease in collagenous protein biosynthesis was observed in the area under the discs containing GPA1734 and [U-14C]proline as compared to control discs containing only the radiolabeled proline. The forementioned effects of GPA1734 on CAM were specific because no similar effects were observed with a closely related compound, 9,10-dihydroxy-7-methyl-benzo[b]quinolizinium bromide or with GPA1734 plus Fe++, which did not affect the rate of BM collagen biosynthesis. These results suggest that inhibitors of BM collagen biosynthesis prevent angiogenesis by interfering with the formation of an essential component of the vessel wall. The search for such inhibitors may be a new approach in the development of antiangiogenic agents.

Tumor-promoting phorbol esters induce angiogenesis in vivo

Abstract: It has been hypothesized that tumor growth is dependent on the concomitant growth of its vascular supply, and thus agents that stimulate angiogenesis may help support tumor growth. Phorbol esters are potent tumor promoters that induce a variety of biochemical effects in cells, including activation of protein kinase C. The specific mechanisms responsible for tumor promotion by phorbol esters are unknown. The objective of this study was to determine whether the tumor-promoting phorbol esters can induce vascular growth. Phorbol esters were tested for their ability to stimulate angiogenesis in vivo using the chick chorioallantoic membrane and rabbit cornea assays. The active tumor promoters 12-O-tetradecanoyl phorbol-13-acetate and phorbol 12,13-didecanoate, which activate protein kinase C, were found to stimulate angiogenesis in a dose-dependent manner. In contrast, 4 alpha-phorbol 12,13-didecanoate, which is inactive as a tumor promoter and does not activate protein kinase C, did not stimulate angiogenesis. Phorbol esters may be indirect angiogenic factors, since no mitogenic effect on bovine capillary endothelial cells in culture could be detected. The results demonstrate that the tumor-promoting activity of phorbol esters may, in part, be secondary to stimulation of neovascularization to support tumor growth and suggest a role for the activation of protein kinase C in this process.

Angiogenic activity of bovine corpora lutea at several stages of luteal development

Abstract: Samples from corpus haemorrhagicum, mid-cycle corpus luteum (CL) and late-cycle CL were tested for their abilities to stimulate neovascularization of chorioallantoic membranes (CAM) of developing chicks. Responses were graded from 0 to 4 (4 being the greatest response). Luteal tissue implants from each stage of the oestrous cycle stimulated growth of CAM blood vessels, and vascular responses increased with age of CL. Implants from late-cycle CL were typically graded 3 or 4. Luteal tissues from several stages of development were also incubated for 6 h in serum-free medium containing no hormone, LH, PGF-2 alpha or both hormones. Media conditioned by luteal tissues were assayed for progesterone and tested for their ability to stimulate mitogenesis and migration of bovine aortic endothelial cells in vitro. All media conditioned by luteal tissues stimulated mitogenesis and migration of endothelial cells, but media from late-cycle CL exhibited the greatest activity. Luteinizing hormone significantly increased in-vitro secretion of a factor(s) that stimulated migration of endothelial cells. PGF-2 alpha alone had no effect on production of endothelial cell mitogen or migration-stimulating factor(s) from luteal incubations; however, the ability of LH to enhance secretion of the migration-stimulating factor(s) was blocked by PGF-2 alpha. This study demonstrates that angiogenic activity of bovine luteal tissues increases with age of the CL and in-vitro secretion of angiogenic factor is responsive to hormones known to regulate luteal function.

Oncogenes and growth factors

Abstract: Certain polypeptide gene products regulate mitosis, differentiation, and other basic biologic functions of cells. These genes and their products are well preserved throughout evolution. Other sets of genes encode receptors for these polypeptides. Polypeptide growth factors can stimulate the cells that express receptors for them. Autocrine growth occurs when a cell produces a growth factor and also expresses receptors for it. When certain genes remain in a permanently switched-on position or are amplified, excessive amounts of growth factors are produced and receptor-positive cells continuously respond, thus achieving illegitimate growth advantage over other cells. Permanently switched-on and/or point-mutated receptor-encoding genes direct the synthesis of truncated receptors that do not need to capture their ligand for signaling receptor activation, thus their cells remain in a permanently activated state. When immortalization and/or malignant transformation results from these activities, the gene is recognized as a protooncogene-oncogene. Acutely transforming retroviruses contain close derivatives of these cellular genes (c-onc----v-onc) obtained through transduction. Genes encoding the synthesis of nontransforming growth factors (angiogenesis factors, colony-stimulating factors, interleukins, etc.) imitate protooncogenes in stimulating the growth and differentiation-dedifferentiation on nonimmortalized cells. Immortalized and malignantly transformed cells may retain receptors to regulatory growth factors that may induced differentiation and/or cessation of mitosis. Growth factors or receptors produced in excess by transformed cells may be neutralized by monoclonal antibodies (McAb) breaking the chain of autocrine or paracrine growth. Protooncogenes-oncogenes may be deactivated by biological response modifiers (dexamethasone, interferons, bacterial toxins, etc.). These interventions may lead to a new treatment modality for the malignant process.

Microangiographic and histologic analysis of the effects of hyperthermia on murine tumor vasculature

Abstract: The effects of hyperthermia on murine tumor vasculature were studied by microangiography and histological examination. The tumors used were SCC VII carcinoma and mammary adenocarcinoma of syngeneic C3H/He mice. For the quantitative analysis of microangiographic changes, the percent (%) vascular area, which was defined as the percentage of opacified tumor vessel area to the entire tumor area, was determined in each microangiogram. The % vascular area after heating in a water bath at 44 degrees C for 30 min was minimized 24 hr after heating in both types of tumors. The histologic study revealed that the initial decrease of the % vascular area was due to congestion, thrombosis, and rupture of tumor vessels, and its subsequent increase was due to angiogenesis. SCC VII was more heat sensitive than mammary adenocarcinoma in terms of tumor growth delay, and tumor vessels of SCC VII were more vulnerable to heat than those of mammary adenocarcinoma. Histological examinations showed a marked difference in the architecture of vessels between the two types of tumors. Tumor vessels of mammary adenocarcinoma were supported by a connective tissue band, whereas those of SCC VII consisted of a single endothelial cell layer. Our findings suggest that the tumor vessels supported by a connective tissue band are less sensitive to heat than those without such support. The vascular damage of SCC VII was temperature dependent, and the critical temperature at which dramatic vascular damage appeared was between 42.7 degrees C and 43.7 degrees C.