Sequences of rDNA internal transcribed spacers from the chloroplast DNA of 26 bryophytes: properties and phylogenetic utility

We determined the sequence of the region of the chloroplast DNA inverted repeat spanning from the 3'-terminus of the 23S rRNA gene to the 5'-terminus of the tRNA[Arg](ACG) gene (about 700 bp) from 25 bryophytes and from the charophycean alga Chara australis. Phylogenetic analysis of these sequences using the neighbor-joining method suggests an early dichotomy of bryophytes and their paraphyly relative to the tracheophyte lineage. A monophyly of liverworts (Marchantiidae plus Jungermanniidae), a deep divergence of Metzgeriales among Jungermanniidae and a close affinity of the two subclasses of mosses, Sphagnidae and Andreaeidae, are evident. The branching pattern observed is consistent with the phylogenetic distribution of several prominent indels observed in the alignment.

Aortic endothelial cells regulate proliferation of human monocytes in vitro via a mechanism synergistic with macrophage colony-stimulating factor. Convergence at the cyclin E/p27(Kip1) regulatory checkpoint

Monocyte-derived macrophages (Mphis) are pivotal participants in the pathogenesis of atherosclerosis. Evidence from both animal and human plaques indicates that local proliferation may contribute to accumulation of lesion Mphis, and the major Mphi growth factor, macrophage colony stimulating factor (MCSF), is present in atherosclerotic plaques. However, most in vitro studies have failed to demonstrate that human monocytes/Mphis possess significant proliferative capacity. We now report that, although human monocytes cultured in isolation showed only limited MCSF-induced proliferation, monocytes cocultured with aortic endothelial cells at identical MCSF concentrations underwent enhanced (up to 40-fold) and prolonged (21 d) proliferation. In contrast with monocytes in isolation, this was optimal at low seeding densities, required endothelial cell contact, and could not be reproduced by coculture with smooth muscle cells. Intimal Mphi isolated from human aortas likewise showed endothelial cell contact-dependent, MCSF-induced proliferation. Consistent with a two-signal mechanism governing Mphi proliferation, the cell cycle regulatory protein, cyclin E, was rapidly upregulated by endothelial cell contact in an MCSFindependent fashion, but MCSF was required for successful downregulation of the cell cycle inhibitory protein p27(Kip1) before cell cycling. Thus endothelial cells and MCSF differentially and synergistically regulate two Mphi genes critical for progression through the cell cycle.

[Molecular biological research on the origin of the angiosperms]

Nucleotide sequence of 23S-5S chloroplast rDNA spacer region including 4.5S rRNA gene of several dozens of seed plants was determined. The data obtained were used to construct phylogenetic trees and to compare them with the analogous data from literature. Topologies of trees constructed for various types of macromolecules and by different methods demonstrate obvious similarities although they are not identical. Some clue stages of seed plants evolution still remain obscure. Critical analysis of all the available information allows to come to several more or less definite conclusions. All the data say that angiosperms are a monophyletic group which diversified far before their fossils are definitely registered, i.e., before lower Cretaceous. Ancestral angiosperms were not genealogicaly related to modern woody Magnoliales but were represented by "paleoherbs", i. e. herbaceous and semiherbaceous magnoliids and monocots. Monocots originated at the earliest stages of angiosperms evolution and are not, probably, monophyletic. Woody Magnoliales and eudicots with tricolpate pollen seem to appear later in evolution. The conclusion that Gnetales is a sister group to angiosperms does not find enough support in molecular studies. Summing up, it looks as if a long period of existence of angiophytes preceded the pre-Cretaceous angiosperms irradiation. This line of development originated simultaneously with phylogenetic lineages of modern gymnosperms.

Secretion of a novel T-lymphocyte cytokine possessing both chemotactic and growth factor activity by serotonin-stimulated human aortic endothelial cells

The development of an extralymphatic T-lymphocyte focus of inflammation requires chemoattractant-induced cell migration and growth factor-induced cell proliferation. In a previous study, we identified a novel 13- to 15-kDa T-lymphocyte-specific chemotactic cytokine, endothelial cell-derived lymphocyte chemoattractant activity (ED-LCA), secreted by serotonin-stimulated human aortic endothelial cells. Based on its physicochemical and functional characteristics and antibody inhibition studies, ED-LCA is distinct from previously identified endothelial cell-derived IL-1, IL-6, and IL-8. Because of the association between T-lymphocyte chemotactic and growth factor activity, in the current study, we investigated the effect of ED-LCA on T cell growth by assessing its capacity to induce markers of the passage of T cells from the resting (G0) state into the G1 phase of the cell cycle, such as receptors for IL-2 (IL-2R) and transferrin (TFR), and class II major histocompatibility complex antigens (HLA-DR). Incubation of G0 freshly isolated human T lymphocytes for 48 h with chromatographically resolved, partially purified ED-LCA resulted in a threefold increase in expression of IL-2R, a threefold increase in TFR, and a twofold increase in HLA-DR. Double antibody labeling demonstrated that IL-2R was induced in both CD4+ and CD8+ T cell subsets. Although incubation of human T cells with ED-LCA alone did not induce DNA synthesis, addition of exogenous IL-2 to T cells pulsed with ED-LCA for 24 h caused an increase in DNA synthesis with a stimulation index of 3.5. By up-regulating functional cell surface receptors for IL-2 on T lymphocytes and priming them to respond to exogenous IL-2, ED-LCA is a competence growth factor. By virtue of its effect on T cells, as a chemotactic and competence factor, this endothelial cell-derived mitoattractant could participate with other T-cell growth factors like IL-2 in the generation of an extralymphatic T-lymphocyte inflammatory response.

[The regional morphological characteristics of the endothelium of the human thoracic aorta in perfusion fixation]

The ultramicroscopic organization and the endotheliocyte surface relief in ventral portions of the thoracic part of human aorta and in zones of division of blood flow were studied under conditions of early post mortem examinations and perfusion fixation of corpses of 14 humans dead from accidental causes. Zones of entrance into the intercostal aortas are compared with the straight portions of the aorta and are found to be characterized, as compared with the latters, by polymorphism of the endothelium, higher adhesiveness of its surface to blood elements, as well as by the presence of intravitally de-endothelialized portions localized on the ridge of the intimal valve.

[Signal-conducting and low molecular weight GTP-binding proteins from the lung and endothelium: localization in membranes and cytosol, interaction with F-actin]

The following proteins have been identified in mammalian lung and endothelium, using [32P]ADP-ribosylation by bacterial ADP-ribosyltransferase, immuno- and [alpha-32P]GTP-blottings: 41 kDa Gi1 alpha, 40 kDa Gi2 alpha, 41 kDa Gi3 alpha, 40 kDa and 45 kDa subunits of GS alpha, 36 kDa beta 1 and 35 kDa beta 2 subunits of signal-transmitting GTP-binding proteins (G-proteins), the 19-26 kDa low molecular weight GTP-binding proteins (SMG-proteins) ras, rho, rac, G25K (Gp), as well as ARF and SMG proteins binding with a high affinity to [alpha-32P]GTP. These G- and SMG-proteins are contained in various proportions in membrane and cytosol fractions of lung and endothelium cells. Subunits Gi2 alpha and GS alpha (but not beta 1 or SMG-proteins) my partially (approximately 1%) dissociate from the membrane by the action of the GTP analogs GTP[S] or Gpp(NH)p in the presence of magnesium ions. Extraction with low ionic strength buffer solutions in the presence of EDTA is accompanied by the release of G-actin sensitive to whooping cough toxin Gi2 alpha and beta i subunits. The functionally coupled into a alpha beta gamma heterodimer Gi-protein subunits (predominantly Gi2 alpha and beta i) present in the cytosol fraction as well as the SMG-proteins revealed by [alpha-32P]GTP-blotting (but not the SMG-proteins sensitive to the botulinic C3 exoenzyme, rho/rac, or ARF, may interact with F-actin. Approximately 20% of these proteins are associated with the Triton X-100 insoluble (cytoskeletal) fraction of the endothelium. A conclusion is drawn that interactions of G- and SMG-proteins with actin filaments may be the reason for the formation of "multidisperse" structure in a cell.

Phenotype related changes of intimal smooth muscle cells from human aorta in primary culture

To study the functional characteristics of smooth muscle cell (SMC) phenotypes, we have investigated myosin expression, cell proliferation, collagen production and low-density lipoprotein (LDL) receptor activity in intimal SMCs of normal human aorta during their growth in primary culture. By staining with rabbit antibodies to smooth muscle myosin (ASMM) 3 cell types could be distinguished in culture: homogeneously stained cells, cells with discontinuous myosin fibrils and myosin-negative cells. The ratio of cell types greatly changed with culture growth: on days 5, 7 and 14 it was 82:1:17%, 70:5:25% and 10:30:60%, respectively. After 5-6 days of culture intimal SMCs began to proliferate and DNA-synthesizing nuclei were seen 1.5-4.3 times more frequently in myosin-negative cells than in cells with homogeneous myosin distribution. At that time the number of cells reacted with monoclonal antibody (MAb) to an epitope shared collagen types I and III started to increase. By double immunofluorescence staining it was shown that the cultured cells containing both ASMM and MAb markers were found 2.0-4.8 times more rarely than MAb-positive staining in myosin-negative cells. During the first 5 days in culture LDL binding and uptake were diminished in intimal cells with intercellular lipid inclusions independently of their myosin staining pattern, but their activity increased with culture growth. Thus, SMCs from human aortic intima change their phenotype on days 6 and 7 in primary culture as manifested by alteration of myosin expression, increased cell proliferation, collagen production and LDL receptor activity. Changes in myosin expression, however, are not an essential prerequisite for cell proliferation and collagen production.

Prothrombotic phenotype diversity of human aortic endothelial cells in culture

We have previously demonstrated that human aortic endothelium exhibits morphologic heterogeneity in situ, and this heterogeneity can be reproduced in culture. In this study, we have compared prothrombotic properties of cultured endothelial cells (EC) from areas of human aorta at high risk for atherosclerosis (HP-EC) with EC from areas at low risk (LP-EC). Using paired cultures from the same donors, we have found that the expression of cell surface thrombomodulin (TM)--as measured by the ability to generate activated protein C (APC) from protein C in the presence of thrombin--is relatively reduced on HP-EC compared to LP-EC (respectively, 4.98 +/- 4.43 vs. 5.83 +/- 4.37 pM APC/min/cm2; p = .03, n = 12). Furthermore, HP-EC more efficiently assemble the prothrombinase complex on their cellular surface, resulting in an increased rate of thrombin generation from prothrombin (9.81 +/- 3.10 (HP-EC) vs. 7.96 +/- 3.20 nM thrombin/min/cm2 (LP-EC); p less than .03, n = 7). The combination of reduced TM expression and increased prothrombinase complex assembly on HP-EC suggests a prothrombotic phenotype in these cells. These findings may be important in the pathogenesis of thrombosis associated with atherosclerotic plaques.

Cytokine secretion by human aortic endothelial cells is related to degree of atherosclerosis

We have previously described a 13- to 15-kDa T-lymphocyte-specific chemotactic protein (endothelial cell-derived lymphocyte chemoattractant activity, ED-LCA) secreted by serotonin-stimulated bovine aortic endothelial cells. In the current study, we have identified a similar serotonin-induced chemotaxin secreted by human aortic endothelial cells (HAEC). Like the bovine ED-LCA, secretion of this human T-cell chemotaxin peaked at 10(-5) M serotonin, was blocked by 5-HT2-receptor antagonists, and was not induced by other vasoactive amines, such as histamine or angiotensin II. In addition, human ED-LCA had no effect on neutrophil or monocyte migration. Using HAEC and human pulmonary arterial endothelial cells (HPAEC) from the same individual, we found that serotonin-stimulated HAEC, but not HPAEC, secreted ED-LCA. Because human vascular endothelium affected by atherosclerosis is morphologically, ultrastructurally, and phenotypically distinct from unaffected areas, we evaluated the secretion of this cytokine from cultured HAEC derived from areas of aorta differentially affected by atherosclerosis. We found that the degree of atherosclerotic involvement of an individual vessel was associated with a decrease in the uptake of serotonin and a reduction in serotonin-induced ED-LCA secretion. In response to serotonin, HAEC derived from atherosclerotic plaques did not secrete ED-LCA, whereas HAEC derived from fatty streaks secreted lesser amounts of ED-LCA than HAEC derived from normal areas. These studies demonstrate that in vivo morphological heterogeneity of HAEC is maintained in vitro and is associated with alterations in function, as measured by cytokine secretion.

Stellate cells of aortic intima: II. Arborization of intimal cells in culture

The present study analyzed effects of different cAMP-elevators on cell morphology in primary culture of human intimal and medial cells from grossly normal and atherosclerotic areas. In primary culture of human aortic cells adenylate cyclase activator forskolin and other cAMP elevators induced arborization of cells, i.e. they reversibly changed the shape of cells. This resulted in the formation of thin branching processes and in the concentration of cytoplasm around the nucleus. In the culture, the shape of the arborized cells resembled that of stellate ones detected in the aortic intima in situ. The arborization of cells was accompanied by destruction of myofilaments. Due to cAMP elevators' effect, most of the arborized cells were exhibited in the cultures isolated from the elastic-hyperplastic layer of the intima. The number of arborized cells was significantly less in the cultures isolated from the musculo-elastic layer and still lesser in those isolated from media. We failed to reveal any significant difference in the number of arborized cells cultured from fatty streaks, atherosclerotic plaques and grossly normal aortic areas. Obtained results suggest that the previously revealed polymorphism of human aortic intimal cells may be accounted for by the cell shape transformations underlined by the mechanism similar to that of arborization in vitro.

A monoclonal antibody, VM64, reacts with a 130 kDa glycoprotein common to platelets and endothelial cells: heterogeneity in antibody binding to human aortic endothelial cells

A new monoclonal antibody (mAb), VM64, reacts with a common antigen on the surface of human platelets and vascular endothelial cells (EC). Under nonreduced conditions it recognized in immunoblotting a protein of 130 kDa both in platelets and EC. VM64 precipitated the same 130 kDa protein from the lysate of surface radioiodinated platelets. Electrophoretic mobility of this protein was not altered by reduction and differed from the bands precipitated by reference mAb against platelet glycoproteins (GP) Ia-IIa, Ib, IIb-IIIa and GMP130. VM64 binding to platelets and EC was specific and saturable. The number of binding sites on platelets was 9.9 +/- 3.5 x 10(3) per platelet and on the surface of EC monolayer -2.40 +/- 0.32 x 10(6) per cell. VM64 also binds to platelets from Glanzmann's thrombasthenia patients which lack GPIIb-IIIa. VM64 did not affect platelet aggregation induced by ADP, collagen, thrombin and ristocetin. In the monolayers of EC from umbilical vein and human aorta, VM64 stained the area at the periphery of the cells adjacent to the cell-cell boundaries. In preconfluent cultures preferential staining was observed at the active leading margins of the cells. Unlike EC cultures from umbilical vein, where all cells were positively stained, in aortic EC cultures some unstained or poorly stained cells were constantly present, indicating a heterogeneity of EC population related to the expression of VM64 antigen. The biochemical characteristics of VM64 antigen, its presence both on platelets and EC and typical distribution on the surface of EC suggested that this antigen is identical to PECAM (CD31) protein.

Angiosperm origin and early stages of seed plant evolution deduced from rRNA sequence comparisons

Complete or partial nucleotide sequences of five different rRNA species, coded by nuclear (18S, 5.8S, and 5S) or chloroplast genomes (5S, 4.5S) from a number of seed plants were determined. Based on the sequence data, the phylogenetic dendrograms were built by two methods, maximum parsimony and compatibility. The topologies of the trees for different rRNA species are not fully congruent, but they share some common features. It may be concluded that both gymnosperms and angiosperms are monophyletic groups. The data obtained suggest that the divergence of all the main groups of extant gymnosperms occurred after the branching off of the angiosperm lineage. As the time of divergence of at least some of these gymnosperm taxa is traceable back to the early Carboniferous, it may be concluded that the genealogical splitting of gymnosperm and angiosperm lineages occurred before this event, at least 360 million years ago, i.e., much earlier than the first angiosperm fossils were dated. Ancestral forms of angiosperms ought to be searched for among Progymnospermopsida. Genealogical relationships among gymnosperm taxa cannot be deduced unambiguously on the basis of rRNA data. The only inference may be that the taxon Gnetopsida is an artificial one, and Gnetum and Ephedra belong to quite different lineages of gymnosperms. As to the phylogenetic position of the two Angiospermae classes, extant monocotyledons seem to be a paraphyletic group located near the root of the angiosperm branch; it emerged at the earliest stages of angiosperm evolution. We may conclude that either monocotyledonous characters arose independently more than once in different groups of ancient Magnoliales or that monocotyledonous forms rather than dicotyledonous Magnoliales were the earliest angiosperms. Judging by the rRNA trees, Magnoliales are the most ancient group among dicotyledons. The most ancient lineage among monocotyledons leads to modern Liliaceae.

Inhibition of cholesterol synthesis by lovastatin tested on six human cell types in vitro

Lovastatin (mevinolin) caused a strong and dose-dependent inhibition of cholesterol synthesis in six types of cultured human cells. Fifty percent inhibition of cholesterol synthesis in human enterocytes was observed at a lovastatin concentration of about 0.004 ng/ml and in other cells at a lovastatin concentration of about 0.03 ng/ml. At lovastatin concentrations between 1.0 and 100.0 ng/ml, a moderate tissue selectivity of lovastatin action was noted. At optimal concentrations, lovastatin inhibited cholesterol synthesis in hepatocytes by 98%, in normal and LDL-receptor negative fibroblasts, arterial smooth muscle cells and hepatoma G-2 cells by about 90%, and in enterocytes by 75%. In rat enterocytes lovastatin inhibited cholesterol synthesis by only 60%.

[Interferon production by primary culture of human endothelial cells]

Endothelial cells of human umbilical vein are capable of producing interferon upon induction with Newcastle disease virus, influenza virus, and poly I: poly C, but not staphylococcal enterotoxin A. All the interferons produced belonged to the alpha-type. After treatment with influenza virus the endothelial cells produce two subtypes of alpha-interferon: acid-labile and acid-stable.

Influence of ions on the structure of water under conditions far away from equilibrium

The paper deals with the influence of electrolytes on the structure temperature of water. The variations in water structure have been investigated by the method of the states spectra of water, i.e. by the distribution function of the wetting angle of water drops, which evaporate under constant conditions. Some results have been obtained about the mechanism of the action of ions, stabilizing and breaking the water structure, on the stable states in the latter under conditions far away from equilibrium.

Mechano-chemical control of human endothelium orientation and size

Human umbilical vein endothelial cells (EC) were grown on elastic silicone membranes subjected to cyclic stretch, simulating arterial wall motion. Stretching conditions (20% amplitude, 52 cycle/min) stimulated stress fiber formation and their orientation transversely to the strain direction. Cell bodies aligned along the same axis after the actin cytoskeleton. EC orientation response was inhibited by the adenylate cyclase activator, forskolin (10(-5) M), which caused stress fiber disassembly and the redistribution of F-actin to the cortical cytoplasm. Preoriented EC depleted of stress fibers by forskolin treatment retained their aligned state. Thus, stress fibers are essential for the process of EC orientation induced by repeated strain, but not for the maintenance of EC orientation. The monolayer formed by EC grown to confluence in conditions of intermittent strain consisted of uniform elongated cells and was resistant to deformation. In contrast, the monolayer assembled in stationary conditions was less compliant and exposed local denudations on initiation of stretching. When stretched in the presence of 10(-5) M forskolin it rapidly (3-4 h) reestablished integrity but gained a heterogeneous appearance since denuded areas were covered by giant cells. The protective effect of forskolin was because of the stimulation of EC spreading. This feature of forskolin was demonstrated while studying its action on EC spreading and repair of a scratched EC monolayer in conventional culture. Thus mechanical deformation and adenylate cyclase activity may be important factors in the control of endothelium morphology in human arteries.

[Phylogenetic analysis of partial nucleotide sequences of 18S rRNA for 14 plant species]

The variable 260 base long region from the interior of 18S rRNA of 14 plant species was determined by chain termination method with the use of reverse transcriptase. The hairpin revealed in this region appeared to be conservative in all species compared. Thermodynamic stability of such hairpin is lower than of an alternative structure with different base pairing mode. From sequence data dendrograms were produced by clustering algorithms and by the compatibility method. In addition to the plant sequences these dendrograms included also the homologous regions from yeast and Xenopus 18S rRNAs. The compatibility method seems to be more reliable. Inferences were drawn on relations between gymnosperms and angiosperms, monocots and dicots on the bases of the analysis of this tree.

Effects of forskolin and phorbol-myristate-acetate on cytoskeleton, extracellular matrix and protein phosphorylation in human endothelial cells

The role that the intracellular mediators, cAMP and Ca2+/phosphatidylserine-dependent protein kinase C, play in the regulation of endothelial cell (EC) motility was investigated. The adenylate cyclase activator, forskolin, at 10 microM induced rapid and reversible alterations in the shape of cultured human EC, disappearance of actin bundles and the concentration of F-actin at cell borders. Actin reorganization provoked by forskolin coincide with redistribution of vinculin to the cell periphery and rapid elimination of surface-associated fibronectin. A protein kinase C activator, phorbol 12-myristate 13-acetate (PMA) at 10-100 microM induced no visible alterations of cell shape, but enhanced the effect of forskolin. PMA stimulated formation of "stress fibers" and increased the number of vinculin plaques in central areas of the cell. A decrease in the amount of the surface-associated fibronectin in PMA-treated cells has also been observed, but, this effect was considerably slower than that produced by forskolin. Forskolin, but not PMA stimulated phosphorylation of the major intermediate filament protein, vimentin.

[The structure of the centriolar apparatus of the endothelial cells in the embryonic and definitive human aorta]

The fine structure of the centriolar system was studied on serial sections of 90 endothelial cells of human aorta (50 to 60 years) in regions without atherosclerotic platelets and with fibrous and atheromatous platelets and of 30 endothelial cells of human embryonic aorta (22-24 weeks). The vast majority (95%) of endothelial cells of the atheromatous platelets were shown to have a primary cilium over 1 micron long which gives on the basal surface in all the cells. In the regions without platelets and with fibrous platelets a cilium was observed in about 20% of cells and it gives in the vessel lumen. Endothelial cells with a cilium fully embedded in the cytoplasm and with abnormal cilium structure were found in the embryonic aorta. A suggestion is put forward that cilia of the endothelial cells of embryonic aorta and those of adult aorta differ by the mechanism of their formation and can have different functions.

Identification of intimal subendothelial cells from human aorta in primary culture

Subendothelial cells (SEC) were obtained from the inner intimal layer of adult human aorta by collagenase treatment. SEC were identified in primary culture either as smooth muscle cells by staining with FITC-labeled antisera against human smooth muscle myosin or as macrophages, foam cells and contaminating endothelial cells by their uptake of malondialdehyde treated low density lipoproteins labeled with fluorescent dye 3,3'-dioctadecylindocarbocyanine. Between 1 and 5 days in culture, along with smooth muscle cells (SMC, 38-82%), endothelial cells (0-9%), macrophages and foam cells (2-32%), one more type of cell was found. This cell type resembled SMC in size and shape, but was not stained by antisera to SMC myosin. By ultrastructural criteria these cells were characterized as modulated SMC for they contained prominent rough endoplastic reticulum and Golgi complex together with basement membrane and a large number of plasmalemmal vesicles. Like SMC they reacted with phalloidin and were stained by anti-vimentin but not by anti-desmin monoclonal antibodies. The proportion of such cells varied from 5 to 33% of total cell number and increased in parallel to macrophages and foam cells in vessels with well developed atherosclerotic lesions. We conclude that the applied technique may be used for identification of cultured vascular cells including modulated SMC.

An ultrastructural study of centriolar complexes in adult and embryonic human aortic endothelial cells

Ultrastructural organization of centriolar complexes in 90 adult human aortic endothelial cells from uninvolved areas, fibrous and atheromatous plaques and 30 endothelial cells from human embryonic aorta were studied using serial sections. Primary cilia protruding from the abluminal cell surface were found on 28 of 30 endothelial cells from atheromatous plaques. Only five of 30 cells from either fibrous plaques or uninvolved areas developed primary cilia protruding to the lumen. Impaired primary cilia entirely immersed into the cytoplasm were found in embryonic endothelial cells. It was speculated that both the modes of formation and the functions of endothelial cilia in embryonic and adult aortas are different.

Morphological alterations in endothelial cells from human aorta and umbilical vein induced by forskolin and phorbol 12-myristate 13-acetate: a synergistic action of adenylate cyclase and protein kinase C activators

The morphological effects on human endothelial cells of phorbol 12-myristate 13-acetate (PMA) and of agents that increase intracellular cAMP concentration were studied. The adenylate cyclase activator forskolin (10 microM), the cyclic nucleotide phosphodiesterase inhibitor methylisobutylxanthine (100 microM), dibutyryl-cAMP (10 microM), histamine (10 microM), and PMA (0.1 microM) significantly altered the morphology of human aortic and umbilical vein endothelial cells in primary cultures. These effects reached a maximum 40-80 min after the effector addition and became negligible 30-60 min after its removal. PMA and forskolin were strongly synergistic in altering endothelial cell morphology. All the effects of cAMP-elevating compounds and of PMA were abolished completely by 1 microM colchicine. In explants taken from human adult or child aortas, forskolin and PMA produced alterations in endothelial morphology qualitatively identical to those observed in endothelial cell cultures. Endothelium in these preparations closely resembled that found in zones of expected altered hemodynamic stresses of human aorta. Our data suggest that the morphology of endothelium in vivo may be regulated by separate or synergistic action of hormone-dependent adenylate cyclase and of inositol phospholipid turnover systems and might be important for maintenance of endothelial monolayer integrity under normal physiological and pathological conditions.