Biomedical subjects

F Yuan

Publications and source records attributed to F Yuan.

At least 73 records · Page 4Linked to original sources

PubMed1996

Quantitation and physiological characterization of angiogenic vessels in mice: effect of basic fibroblast growth factor, vascular endothelial growth factor/vascular permeability factor, and host microenvironment.

A prerequisite for the development of novel angiogenic and anti-angiogenic agents is the availability of routine in vivo assays that permit 1) repeated, long-term quantitation of angiogenesis and 2) physiological characterization of angiogenic vessels. We report here the development of such an assay in mice. Using this assay, we tested the hypothesis that the physiological properties of angiogenic vessels governed by the microenvironment and vessel origin rather than the initial angiogenic stimulus. Gels containing basic fibroblast growth factor (bFGF) or vascular endothelial growth (VEGF) were implanted in transparent windows in the dorsal skin or cranium of mice. Vessels could be continuously and non-invasively monitored and easily quantified for more than 5 weeks after gel implantation. Newly formed vessels were first visible on day 4 in the cranial window and day 10 in the dorsal skinfold chamber, respectively. The number of vessels was dependent on the dose of bFGF and VEGF. At 3000 ng/ml, bFGF- and VEGF-induced blood vessels had similar diameters, red blood cell velocities, and microvascular permeability to albumin. However, red blood cell velocities and microvascular permeability to albumin were higher in the cranial window than in the dorsal skinfold chamber. Leukocyte-endothelial interaction was nearly zero in both sites. Thus, newly grown microvessels resembled vessels of granulation and neoplastic tissue in many aspects. Their physiological properties were mainly determined by the microenvironment, whereas the initial angiogenic response was stimulated by growth factors.

Animals↗

PubMed1996

[Experimental study on adenosine hypothesis of bradyarrhythmias occurring in myocardial hypoxia and its clinical significance].

Important role of endogenous adenosine in the pathogenesis of hypoxic bradyarrhythmias was verified experimentally both in vivo and in vitro models of myocardial hypoxia in 180 guinea pigs and 40 rabbits by using enzyme differential spectrophotometry, synchronous quantitative analysis of correlated factors and adenosine antagonist. Results disclosed that endogenous adenosine in hypoxic myocardium increased markedly from a gram myocardial tissue 5.8 +/- 1.7 nmol of the control group to 27.5 +/- 2.0 nmol of 5% O2 inhalation group (P < 0.01). Sinus bradycardia and A-V block induced by injection of exogenous adenosine were closely akin to those caused by myocardial hypoxia both in ECG characteristics and dose-response curve. Both of their His electrograms showed prolongation of A-H interval but nochange of H-V interval, indicating the same locality of conduction block. Synchronous quantitative analysis of 3 related factors revealed a correlation coefficient of 0.99 (P < 0.01) between endogenous adenosine and bradyarrhythmias, denoting a subordinate instead of coordinate relation. Moreover, cause and effect relation could be shown between them from the result that aminophylline (50 mg, i.p.) could abolish completely II degrees-III degrees A-V block which would otherwise be bound to occur after inhalation of 5% O2. The present study is the first in vivo experimental verification of adenosine hypothesis throughout the world which not only can well explain those atropine-resistant cases, but also opens up the way to an entirely new therapeutic strategy for these kinds of bradyarrhythmias, i.e. instead of M-cholinoceptor blocker, adenosine antagonist (methylxanthines, e.g. aminophylline) should be prescribed.

Adenosine↗

PubMed1996

Glutamate-induced swelling of cultured astrocytes is mediated by metabotropic glutamate receptor.

The effects of glutamate and its agonists and antagonists on the swelling of cultured astrocytes were studied. Swelling of astrocytes was measured by [3H]-O-methyl-D-glucose uptake. Glutamate at 0.5, 1 and 10 mmol/L and trans-1-aminocyclopentane-1, 3-dicarboxylic acid (trans-ACPD), a metabotropic glutamate receptor (mGluR) agonist, at 1 mmol/L caused a significant increase in astrocytic volume, whereas alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) was not effective. L-2-amino-3-phosphonopropionic acid (L-AP3), an antagonist of mGluR, blocked the astrocytic swelling induced by trans-ACPD or glutamate. In Ca(2+)-free condition, glutamate was no longer effective. Swelling of astrocytes induced by glutamate was not blocked by CdCl2 at 20 mumol/L, but significantly reduced by CdCl2 at 300 mumol/L and dantrolene at 30 mumol/L. These findings indicate that mGluR activation results in astrocytic swelling and both extracellular calcium and internal calcium stores play important roles in the genesis of astrocytic swelling induced by glutamate.

Animals↗

PubMed1995

Rolling in P-selectin-deficient mice is reduced but not eliminated in the dorsal skin.

P-selectin-mediated rolling is believed to be important in the recruitment of leukocytes to tissue after ischemia-reperfusion injury. The dorsal skin chamber was used to examine differences in the rolling and stable adhesion of circulating leukocytes in subcutaneous (SC) vessels of P-selectin-deficient and age-matched wild-type mice, both under basal conditions and after ischemia-reperfusion. Rolling in the postcapillary venules in SC tissue of P-selectin-deficient mice was significantly lower than that in wild-type mice under the basal conditions and post-ischemia-reperfusion (P < .05), but was not eliminated by the deletion of the P-selectin gene. No significant difference between P-selectin-deficient and wild-type mice in shear rate or leukocyte-endothelial adhesion was observed up to 24 hours after ischemia-reperfusion. These results show that P-selectin-mediated rolling is not a prerequisite for ischemia-reperfusion-induced leukocyte-endothelial adhesion in the skin.

Animals↗

PubMed1995

Vascular permeability in a human tumor xenograft: molecular size dependence and cutoff size.

Molecular size is one of the key determinants of transvascular transport of therapeutic agents in tumors. However, there are no data in the literature on the molecular size dependence of microvascular permeability in tumors. Therefore, we measured microvascular permeability to various macromolecules in the human colon adenocarcinoma LS174T transplanted in dorsal skin chambers in severe combined immunodeficient mice. These molecules were fluorescently labeled and injected i.v. into mice. The microvascular permeability was calculated from the fluorescence intensity measured by the intravital fluorescence microscopy technique. The value of permeability varied approximately 2-fold in the range of molecular weight from 25,000 to 160,000. These data indicate that tumor vessels are less permselective than normal vessels, presumably due to large pores in the vessel wall. The transport of macromolecules appears to be limited by diffusion through these pores. The cutoff size of the pores was estimated by observations of transvascular transport of sterically stabilized liposomes of 100-600 nm in diameter. We found that tumor vessels in our model were permeable to liposomes of up to 400 nm in diameter, suggesting that the cutoff size of the pores is between 400 and 600 nm in diameter.

Animals↗

PubMed1995

Evaluation of comparative protein modeling by MODELLER.

We evaluate 3D models of human nucleoside diphosphate kinase, mouse cellular retinoic acid binding protein I, and human eosinophil neurotoxin that were calculated by MODELLER, a program for comparative protein modeling by satisfaction of spatial restraints. The models have good stereochemistry and are at least as similar to the crystallographic structures as the closest template structures. The largest errors occur in the regions that were not aligned correctly or where the template structures are not similar to the correct structure. These regions correspond predominantly to exposed loops, insertions of any length, and non-conserved side chains. When a template structure with more than 40% sequence identity to the target protein is available, the model is likely to have about 90% of the mainchain atoms modeled with an rms deviation from the X-ray structure of approximately 1 A, in large part because the templates are likely to be that similar to the X-ray structure of the target. This rms deviation is comparable to the overall differences between refined NMR and X-ray crystallography structures of the same protein.

Amino Acid Sequence↗

PubMed1995

Quantitative analysis of angiogenesis and growth of bone: effect of indomethacin exposure in a combined in vitro-in vivo approach.

Nonsteroidal anti-inflammatory agents have been used experimentally and clinically to suppress a variety of physiological events, including angiogenesis and formation of bone. The exact mechanisms by which indomethacin alters skeletal tissue generation are unknown, due in part to methodological limitations. By the use of an organ culture assay and an animal model using intravital microscopy in mice bearing dorsal skinfold chambers, the effect of indomethacin on growth and angiogenesis of neonatal femora was characterized over 16 days. In both assays, femora significantly elongated with time (P < 0.05). The in vitro growth rate was more rapid than in vivo and dependent on the serum concentration, culture medium and age of mice. Although enhancing the serum content promoted cellular proliferation in organ culture, it dose-dependently suppressed femoral elongation, leading at 20% fetal calf serum to growth rates identical to those observed in vivo. Indomethacin supplementation (2 and 10 mg l-1) significantly accelerated longitudinal femoral growth in organ culture (P < 0.05), whereas in vivo indomethacin (2 mg kg-1) did not modulate either angiogenesis or elongation of bone. Our in vitro data propose a central role of serum in the regulation of bone formation. Although indomethacin altered femoral growth in vitro, our findings do not suggest that indomethacin suppresses angiogenesis or growth of bone in vivo. The complexity of physiological events in vivo may be obscuring a detectable effect.

Animals↗

PubMed1994

Vascular permeability and microcirculation of gliomas and mammary carcinomas transplanted in rat and mouse cranial windows.

Many brain tumors are highly resistant to chemotherapy, presumably due to the presence of a tight blood-tumor barrier. For a better understanding of the regulation of this barrier by the brain environment, a new intravital microscopy model was established by transplanting tumor tissue into cranial windows in both rats and mice. The model was characterized by RBC velocities, vessel diameters, and vascular permeabilities of various tumors: R3230AC (a rat mammary adenocarcinoma), MCaIV (a mouse mammary adenocarcinoma), and U87 and HGL21 (human malignant astrocytomas). Our results showed that tumor blood flow in cranial windows was one to three orders of magnitude lower than the blood flow in pial vessels and similar to that in dorsal skin-fold chambers observed in previous studies. The mean vessel diameter ranged from 6.8 +/- 1.3 microns for HGL21 to 30.4 +/- 8.5 microns for MCaIV. At least one order of magnitude difference in vascular permeability to albumin was observed between tumor lines: 0.11 +/- 0.05 x 10(-7) cm/s for HGL21 versus 3.8 +/- 1.2 x 10(-7) cm/s for U87. The low vascular permeability of HGL21, which was also confirmed by both sodium fluorescein and Lissamine green injections, suggests that not all tumors are leaky to tracer molecules and that the blood-tumor barrier of this tumor still possesses some characteristics of blood-brain barrier as observed in other intracranial tumors. The model presented here will allow us to manipulate the vascular permeability in brain tumors and thus may provide new information on the regulation of the blood-tumor barrier and new strategies for improving drug delivery in brain tumors.

Animals↗

PubMed1994

Microvascular permeability and interstitial penetration of sterically stabilized (stealth) liposomes in a human tumor xenograft.

Microvascular permeability and interstitial penetration of sterically stabilized liposomes in both normal s.c. tissue and human colon adenocarcinoma LS174T xenograft were quantified by using the dorsal skin-fold chamber implanted in severe combined immunodeficient mice and intravital fluorescence microscopy. Significant extravascular accumulation was the dominant feature of liposome distribution in tumors, whereas only minimal intramural accumulation in postcapillary and collecting venules was observed in normal s.c. tissue. The extravasated liposomes in tumors distributed heterogeneously and formed perivascular clusters that did not move significantly and could be observed for up to 1 week. The effective permeability of tumor vessels to liposomes (2.0 +/- 1.6 x 10(-8) cm/s; n = 23) was six times smaller than that to bovine serum albumin (1.2 +/- 0.5 x 10(-7) cm/s; n = 6). These results provide new insights into the mechanisms of transendothelial pathways of liposomes and improvements in liposome-mediated drug delivery.

Adenocarcinoma↗

PubMed1994

Effect of beta-lymphocyte- and NPC-derived EBV-LMP1 gene expression on in vitro growth and differentiation of human epithelial cells.

The effect of expression of the Epstein-Barr-virus (EBV) latent membrane protein (LMP1) derived from B-lymphocytes (B) and nasopharyngeal carcinoma (NPC) (C) on the in vitro growth and differentiation of a human keratinocyte line, Rhek-1, was analyzed in clonal growth and in in vitro differentiation assays. In contrast to the polygonal parental cells, the B-LMP1-expressing sublines were spindle-shaped while the C-LMP1-expressing cells were pleomorphic. Both B- and C-LMP1-expressing sublines showed increased proliferation as evidenced by: (1) higher colony-forming efficiency (CFE) and larger colony size at reduced serum levels; (2) an increased number of epithelial cell layers formed in the air-liquid-interface culture system and (3) increased expression of proliferative cell nuclear antigen (PCNA). At low serum concentration, the C-LMP1-expressing sublines formed larger colonies than those expressing B-LMP1. In the air-liquid-interface culture system, both B- and C-LMP1-expressing lines showed reduced epithelial differentiation resulting in reduced stratification and reduced involucrin expression similar to those of the cancer cell line, Siha. The results of the present study indicate that the expression of LMP1 in human keratinocytes is associated with morphological transformation and predisposes these cells to a more neoplastic phenotype. The structural difference between the 2 genes responsible for the functional differences and transforming ability will be pinpointed in further experiments.

Antigens, Viral↗

PubMed1994

Noninvasive measurement of microvascular and interstitial oxygen profiles in a human tumor in SCID mice.

Simultaneous measurements of intravascular and interstitial oxygen partial pressure (PO2) in any tissue have not previously been reported, despite the importance of oxygen in health and in disease. This is due to the limitations of current techniques, both invasive and noninvasive. We have optically measured microscopic profiles of PO2 with high spatial resolution in subcutaneous tissue and transplanted tumors in mice by combining an oxygen-dependent phosphorescence quenching method and a transparent tissue preparation. The strengths of our approach include the ability to follow PO2 in the same location for several weeks and to relate these measurements to local blood flow and vascular architecture. Our results show that (i) PO2 values in blood vessels in well-vascularized regions of a human colon adenocarcinoma xenograft are comparable to those in surrounding arterioles and venules, (ii) carbogen (95% O2/5% CO2) breathing increases microvascular PO2 in tumors, and (iii) in unanesthetized and anesthetized mice PO2 drops to hypoxic values at < 200 microns from isolated vessels but drops by < 5 mmHg (1 mmHg = 133 Pa) in highly vascularized tumor regions. Our method should permit noninvasive evaluations of oxygen-modifying agents and offer further mechanistic information about tumor pathophysiology in tissue preparations where the surface of the tissue can be observed.

Adenocarcinoma↗

PubMed1994

Flow velocity in the superficial lymphatic network of the mouse tail.

The present study had two goals: 1) to establish an animal model in which a large network of the initial lymphatics of the skin can be investigated in vivo and 2) to measure effective flow velocity (defined as axial component of the flow velocity) in the lymph capillary network of the skin for the first time. A fluorescence microlymphography technique was used to stain the lymph capillaries in the superficial layer of the skin of the nude mouse tail in 10 female animals (mean age 45.8 +/- 2.4 days; mean wt 21.2 +/- 0.8 g). With the use of densitometric image analysis, effective flow velocity along the tail was measured. The network consisted of a honeycomb-like layer of hexagonally shaped meshes that could be stained in all animals. Effective lymph flow velocities were in the range of 1.4-20.4 microns/s with a mean value of 7.7 +/- 5.9 microns/s; median value was 6.2 microns/s (4.5-10.5; 25 and 75% percentiles). This new animal model allows studies of a large network of lymph capillaries in the skin and should provide new insight into the physiology and pathophysiology of the initial lymphatics.

Animals↗

PubMed1994

Angiogenesis and growth of isografted bone: quantitative in vivo assay in nude mice.

BACKGROUND: Understanding the regulation of vascularization and formation of bone after skeletal trauma is essential for the development of methods to promote healing. The lack of information on the biology of bone healing led us to establish an experimental model that facilitates the in vivo assessment of angiogenesis and growth of bone. EXPERIMENTAL DESIGN: Fresh, cryopreserved (frozen in the presence or absence of 10% dimethyl sulfoxide (DMSO)) or boiled neonatal femora were transplanted into dorsal skin fold chambers in adult mice of the identical strain, and angiogenesis and growth were monitored over 16 days. Computerized analysis of brightfield and epifluorescence images was employed to characterize the process of angiogenesis. Bone formation was quantified in vivo by the use of oxytetracycline. RESULTS: Reperfusion of pre-existing blood vessels of the graft was observed only in fresh transplanted femora, whereas femora of all experimental groups elicited angiogenic response from the host tissue. The rank order of the angiogenic response was: fresh > cryopreservation with DMSO > cryopreservation without DMSO > boiled. Growth of femora was completely abolished after cryopreservation or boiling. Only fresh transplanted femora increased in length (95 microns/day) and in cartilage diameter (41 microns/day). CONCLUSIONS: Our study demonstrates that (a) angiogenesis and growth of transplanted femora can be chronically assessed using in vivo microscopy; (b) the introduction of oxytetracycline for in vivo fluorescence microscopy allows the differential quantification of bone and cartilage growth; and (c) cryoprotection using DMSO enhances restoration of angiogenic potency after freezing. We consider this assay an excellent experimental model to study in vivo effects of agents or procedures that potentially modulate angiogenesis and growth of bone.

Animals↗

PubMed1993

Microvascular permeability of albumin, vascular surface area, and vascular volume measured in human adenocarcinoma LS174T using dorsal chamber in SCID mice.

A novel method was developed to measure the effective permeability of microvessels in three-dimensional tumors. Two unique features characterized our approach: (i) Texas Red (with peak excitation and peak emission wavelengths of 596 and 615 nm, respectively) was used for macromolecular labeling, to minimize the absorption of fluorescence light by hemoglobin in blood. Thus the tumor tissue could be treated approximately as a uniform medium with respect to light absorption. (ii) The light absorption and scattering in tumor tissues were accounted for in relating the fluorescence intensity to the amount of Texas Red-labeled macromolecules extravasated. The vascular permeability of Texas Red-labeled bovine serum albumin in human tumor xenograft LS174T implanted in dorsal skin-fold chamber in severe combined immunodeficient mice was measured using this method. The average permeability-surface area product per unit volume (PS/V, x 10(-4) sec-1) and the average effective permeability (P, x 10(-7) cm/sec) were found to be 1.26 +/- 0.72 and 6.06 +/- 4.30, respectively; the fractional volume of tumor vessels (Vves/V, %) was found to be 9.2 +/- 2.9, and the total surface area of vessels per unit volume (S/V, cm2/cm3) was found to be 239 +/- 82. The errors in the estimation of these parameters are discussed. The method described here is general and can be adapted to study the microvascular permeability of superficial tumors in various organs in patients or animals.

Adenocarcinoma↗

PubMed1993

Fluorescence photobleaching with spatial Fourier analysis: measurement of diffusion in light-scattering media.

A new method for the measurement of diffusion in thick samples is introduced, based upon the spatial Fourier analysis of Tsay and Jacobson (Biophys. J. 60: 360-368, 1991) for the video image analysis of fluorescence recovery after photobleaching (FRAP). In this approach, the diffusion coefficient is calculated from the decay of Fourier transform coefficients in successive fluorescence images. Previously, the application of FRAP in thick samples has been confounded by the optical effects of out-of-focus light and scattering and absorption by the sample. The theory of image formation is invoked to show that the decay rate is the same for both the observed fluorescence intensity and the true concentration distribution in the tissue. The method was tested in a series of macromolecular diffusion measurements in aqueous solution, in agarose gel, and in simulated tissue consisting of tumor cells (45% v/v) and blood cells (5% v/v) in an agarose gel. For a range of fluorescently labeled proteins (MW = 14 to 600 kD) and dextrans (MW = 4.4 to 147.8 kD), the diffusion coefficients in aqueous solution were comparable to previously published values. A comparison of the spatial Fourier analysis with a conventional direct photometric method revealed that even for the weakly scattering agarose sample, the conventional method gives a result that is inaccurate and dependent on sample thickness whereas the diffusion coefficient calculated by the spatial Fourier method agreed with published values and was independent of sample thickness. The diffusion coefficient of albumin in the simulated tissue samples, as determined by the spatial Fourier analysis, varied slightly with sample thickness. In contrast, when the same video images were analyzed by direct photometric analysis, the calculated diffusion coefficients were grossly inaccurate and highly dependent on sample thickness. No simple correction could be devised to ensure the accuracy of the direct photometric method of analysis.These in vitro experiments demonstrate the advantage of our new analysis for obtaining an accurate measure of the local diffusion coefficient in microscopic samples that are thick (thickness greater than the microscope depth of focus) and scatter light.

Biopolymers↗

PubMed1992

Angiogenesis, microvascular architecture, microhemodynamics, and interstitial fluid pressure during early growth of human adenocarcinoma LS174T in SCID mice.

To date, most quantitative information on tumor angiogenesis, microcirculation, and transport has been derived from rodent tumors grown in transparent chamber preparations. In this paper we present a chamber technique adapted to immunodeficient mice for the study of human tumor xenografts. Microcirculatory parameters in severe combined immunodeficient mice bearing a dorsal skin fold chamber preparation were quantified using intravital microscopy and image analysis. The take rate of the human colon adenocarcinoma LS174T in the chamber preparation was 100%, and the tumor area doubling time was 6.5 days. Three days following implantation of 2 x 10(5) tumor cells onto the striated skin muscle, capillary sprouts were noted in the tumor cell mass. Microvasculature in the tumors was established after 10 days. Capillary density, vessel diameter, red blood cell velocity, and blood flow rates in individual microvessels measured on days 10, 14, 18, and 22 showed no statistical difference in the striated muscle (capillaries) and subcutaneous tissue (arterioles and venules) of the skin of tumor-free animals (N = 6), whereas these parameters increased slightly, but not significantly, in the LS174T tumors (N = 7). Mean interstitial fluid pressure (+/- SD) in these small tumors was 4.6 +/- 1.7 mmHg (N = 4) on day 10 and 5.1 +/- 0.9 mmHg (N = 4) on day 22 and significantly elevated compared to that in the subcutaneous and skin tissue (-0.9 +/- 0.8 mmHg) (N = 4) (P < 0.001). To our knowledge, this is the first model enabling intravital microscopic studies of human tumor xenografts in a transparent chamber preparation in severe combined immunodeficient mice. Studies on angiogenesis, microcirculation, and transport using such a preparation should provide new insights into microcirculation-mediated mechanisms for cancer treatment.

Adenocarcinoma↗

PubMed1992

Pharmacokinetic analysis of the perivascular distribution of bifunctional antibodies and haptens: comparison with experimental data.

A mathematical model is developed to describe the concentration profiles around individual tumor blood vessels for two-step approaches to cancer treatment. The model incorporates plasma pharmacokinetics, interstitial diffusion, reversible binding between antibody and hapten and between antibody and tumor-associated antigens, and physiological parameters to evaluate present experimental approaches and to suggest new guidelines for the effective use of two-step approaches. Results show considerable interaction between the binding kinetics, initial drug doses, and antigen density, with optimal parameter ranges depending on the desired goal: treatment or detection. The hapten concentration in tumors was found to be nonuniform because of specific binding to antibodies. While binding of the hapten to the bifunctional antibody is necessary for improved retention, too large a binding affinity may lead to very poor penetration of the hapten into regions far away from blood vessels. The time delay between antibody and hapten injection was found to be an important parameter. Longer time delays were found to be advantageous, subject to constraints such as internalization of the antibody and tumor growth during treatment. A proper combination of initial doses for the two species was also seen to be crucial for maximum effectiveness. Comparison of the model with the experimental data of Le Doussal et al. (Cancer Res., 51: 6650-6655, 1991) and Stickney et al. (Cancer Res., 50: 3445-3452, 1990) suggests two novel, yet testable, hypotheses: (a) the early pharmacokinetics of low molecular weight agents can have an important effect on later concentrations using two-step approaches; and (b) metabolism may play an important role in reducing concentrations in the tumor and tumor:plasma concentration ratios. These results should help in the effective design of two-step strategies.

Antibodies, Neoplasm↗

PubMed1992

Adenosine's role in the genesis of bradyarrhythmias induced by acute myocardial hypoxia.

A close or even causal relation between myocardial adenosine and bradyarrhythmias during acute myocardial hypoxia was testified in guinea pig, rabbit and dog mainly by using specific competitive antagonist and synchronous quantitative analysis of 3 variables: intensity of myocardial hypoxia, degree of endogenous adenosine increment and severity of bradyarrhythmias. Results disclosed: A) striking resemblance of the bradyarrhythmias with hypoxic origin to those caused by exogenous adenosine, B) same locality of A-V conduction block induced by both myocardial hypoxia and exogenous adenosine, C) precise parallelism among the above-listed 3 variables with very high correlativity (r = 0.99, P < 0.01), D) frequent accompaniment of reversal of hypoxic bradyarrhythmias through resupply of 21% O2 with normalization of preexisted increase in myocardial adenosine, E) satisfactory blockade of hypoxic bradyarrhythmias by adenosine's specific antagonist--aminophylline and their augmentation by adenosine's uptake inhibitor--dipyridamole, F) close similarity of the characteristic curve representing relation among the above 3 variables to that among intensity of myocardial hypoxia, degree of endogenous adenosine increment and amount of coronary blood flow in which adenosine's role as a mediator has been well documented and G) reproducible persistence of bradyarrhythmias during myocardial hypoxia irrespective of preliminary vagotomy and atropinization, denoting independence of the occurrence of such dysarrhythmias upon vagal drive, suggestive of a mechanism other than vagotonia. We advocated that hypoxia-induced bradyarrhythmias was caused by increment in endogenous adenosine.

Adenosine↗