Reduction of severe ischemia/reperfusion injury in rat kidney grafts by a soluble P-selectin glycoprotein ligand.

BACKGROUND: Inflammatory leukocyte-endothelium interactions, mediated by selectins, contribute to renal ischemia/reperfusion (I/R) injury. We examined the influence of the soluble P-selectin glycoprotein ligand 1 (sPSGL) on early I/R-induced changes in a rat kidney transplantation model with long cold ischemia. METHODS: After 24 hr of cold storage, syngeneic kidneys were grafted into bilaterally nephrectomized rats. Before transplantation, recipients received either 1 mg/kg of sPSGL or vehicle (n=8 per group). Six hours after reperfusion, grafts were removed for light microscopy and immunohistochemistry. Capillary blood flow was measured under a fluorescence microscope by using the concentric-circles method. RESULTS: A greater proportion, 74.7+/-7.2% (sPSGL) vs. 28+/-7.4% (controls), of all dye-labeled outer medullary capillaries appeared in the 12-microm radius (P<0.01), indicating dense blood flow, whereas 7.6+/-2.9% vs. 43.3+/-9.7%, respectively, appeared in the 60-microm radius (P<0.05), indicating rarefied blood flow. In the sPSGL-treated group, the extent of severe tubular damage within the inner stripe of the outer medulla was lower compared with controls (37.5+/-8.3% vs. 78.4+/-3.5%, P<0.01). Outer medullary heat shock protein 72 expression was 14.5+/-1.6% in the sPSGL-treated group compared with 9.6+/-1.4% in controls (P<0.05). The number of infiltrating polymorphonuclear leukocytes was similar in both groups. Treatment with sPSGL had no influence on the serum creatinine level. CONCLUSIONS: Our data suggest that impairment of outer medullary blood flow is crucial in I/R injury of kidney grafts with prolonged cold storage. Reduction of capillary blood flow perturbations by sPSGL protects tubular cells from severe structural damage. Blocking early selectin-mediated leukocyte adhesion may have therapeutic implications in improving the prognosis of renal transplants with severe I/R injury.

Mapping of capillary flow, cellular redox state, and resting membrane potential in hypoperfused rat myocardium.

The influence on myocyte viability of ischemia-induced changes in capillary perfusion was studied in the hearts of anesthetized rats subjected to partial occlusion of the left coronary artery for 45 min. Timed plasma labeling was applied to determine perfusion patterns. Changes in the fluorescence of preloaded potential-sensitive dyes [tetramethylrhodamine methyl ester (TMRM) and bis-oxonol], of trypan blue, and of endogeneous NADH were utilized in characterizing myocyte viability in histological sections of the heart. Within the hypoperfused zone, localized areas appeared vascularly nonlabeled for periods of at least 10 min. Within these areas a reduction in TMRM fluorescence occurred in 82. 5% of the tissue, signaling a reduced resting membrane potential. In the same areas 37.7% of the myocytes revealed an NADH fluorescence lower than that regularly found in anoxic tissues. This correlated with an especially low level of TMRM, with increased fluorescence bis-oxonol and with an accumulation of trypan blue. In conclusion, in localized hypoperfusion-induced zones lacking capillary flow, an inhomogeneous pattern of reductions in myocyte viability develops, which appears to be relevant in ischemia-induced arrhythmias.

Erucylphosphocholine: pharmacokinetics, biodistribution and CNS-accumulation in the rat after intravenous administration.

The clinical use of alkylphosphocholines (APC) in cancer patients is restricted because of the high gastrointestinal toxicity and the need for oral administration. Therefore we evaluated the clinical pharmacology of erucylphosphocholine (ErPC), the first derivative of the APC family suitable for intravenous administration with strong antineoplastic activity, in vitro and in vivo in rats. The pharmacokinetic parameters after a single intravenous dose of 40 mg/kg were calculated using a two-compartment model: C(max) = 1.6 +/- 0.3 micromol/ml, T(1/2alpha) = 0.18 +/- 0.09 h, T(1/2beta) = 3.3 +/- 0.88 h, clearance = 9.7 +/- 1.2 ml/h, AUC = 2.5 +/- 0.3 micromol/ml per h and Vss = 40.4 +/- 7.9 ml. Biodistribution studies were performed after repeated ErPC administration at different doses. Intravenous injections of 20 mg/kg given at intervals of 48 h for up to 4 weeks were well tolerated. Neither clinical evaluation nor laboratory parameters (haematology and clinical chemistry) revealed toxic side effects. In contrast, higher doses of ErPC (40 mg/kg per 48 h) led to weight loss. After 2 and 4 weeks of therapy with 20 mg/kg per 48 h a high ErPC accumulation was found in the adrenal glands, small intestine and brain. The brain to serum concentration ratios averaged 2.1 after 2 weeks and 4.5 after 4 weeks. Significant leucocytosis and thrombocytosis were observed after 4 weeks of ErPC treatment. The findings suggest that ErPC is a suitable candidate for clinical trials. In particular, owing to the high accumulation in brain tissue, ErPC is a potential agent for chemotherapy against malignant brain tumours.

Changes in renal microcirculation induced by infusion of (Fe3+)-and (Fe2+)-myoglobin during hemorrhagic hypotension in the anesthetized rat: influence of L-NAME and 8-Br-cyclic GMP.

The effects of myoglobin on renal microcirculation were studied in anesthetized rats subjected to hemorrhagic hypotension. Capillary flow distribution was determined by allowing two dyes to circulate for 3 and 1 min, respectively, freezing the left kidney and quantifying the dye distribution in histological sections by analyzing the distances of regularly spaced test points to the next dye-labeled capillary. Control experiments showed 88% of distances to be < 12 microns in the cortex [medullary outer stripe (OS): 77%, inner stripe (IS): 93%] and no distance to be > 60 microns. Myoglobin induced disturbances in intrarenal perfusion with a significantly higher potency of (Fe2+)- as compared to (Fe3+)-myoglobin. With the reduced species, the fraction of distances > 60 microns increased to 54% in the cortex (OS: 69%; IS: 67%). L-NAME, an inhibitor of nitric oxide synthesis, induced similar defects of perfusion. The cGMP analogue 8-Br-cGMP was able to nearly completely prevent these effects. The results support the view that myoglobin when released during hemorrhagic hypotension impairs renal microcirculation supposedly by scavenging the endogenous relaxing factor nitric oxide.

Capillary perfusion pattern and microvascular geometry in heterogeneous hypoxic areas of hypoperfused rat myocardium.

The origin of heterogeneities in tissue oxygenation due to low-flow ischemia was studied in hypoperfused myocardium of anesthetized rats. In frozen sections of myocardial biopsies the localization of increases in NADH fluorescence, an indicator of tissue hypoxia, was compared with microvascular flow distribution and capillary geometry. The latter parameters were accomplished through capillary labeling with indicator dyes in vivo and enzyme-histochemical staining in vitro, respectively. Most NADH-fluorescent areas were found to have developed despite sustained capillary flow. When the fractions of arterial, venous, and intermediate capillary segments were analyzed within circumscribed hypoxic fields (< 200 microns diam), frequencies of 30.7 +/- 6.1, 35.3 +/- 5.3, and 30.8 +/- 5.0%, respectively, were found. In contrast, a significantly higher fraction of arterial segments (63.2 +/- 3.3%) and a lower percentage of venous segments (16.4 +/- 2.5%) were determined in nonhypoxic islands enclosed by hypoxic tissue. These results support the view that the latter zones are located near the arterial portion of the capillary bed where their oxygenation is favored during low-flow states. This effect appears to contribute to the supply heterogeneities in hypoperfused myocardium.

Disturbances in renal microcirculation induced by myoglobin and hemorrhagic hypotension in anesthetized rat.

The question was studied of whether myoglobin (Mb), when released into the general circulation during hemorrhagic hypotension (HH), causes disturbances of renal blood flow. In anesthetized rats 250 mg/kg Mb was intravenously infused within 1 h; HH at 50 mmHg with subsequent retransfusion was induced for 30 min. By allowing two dyes to circulate for 1 and 3 min, respectively, and detecting their localization histologically after rapid freezing of the organ, intrarenal distribution of capillary blood flow was studied. In contrast to the results obtained with Mb or HH alone, when Mb was infused during HH, the development of large areas within cortex and medulla lacking any capillary perfusion was observed. In > 70% of the tissue, a distance > 60 microns to the next dye-labeled capillary was found (in controls 0%). At this time total renal flow had decreased from 5.3 to 0.20 ml/min (HH without Mb: 5.1 to 1.1 ml/min). It is concluded that the observed changes in renal blood flow contribute to the known direct nephrotoxic potential of Mb.

Pulmonary uptake of bupivacaine in isolated perfused rat lung.

The ability of rat lung to remove the local anaesthetic drug bupivacaine from the blood was studied in isolated organs which were perfused either in an open (single-pass mode) or in a closed system (recirculating medium). Isolated perfused rat lungs exhibited a very low capacity to metabolize bupivacaine within 3 h during which the drug circulated continuously through the organ. The clearance values differed only by 0.2 ml/min from the control parameters in sham perfusions. The calculated extraction ratio was 0.2% and the elimination half-life was about 210 min. The volume of distribution of bupivacaine was 133 ml which remarkably surmounted the reference values obtained for sham perfusions. The distribution of bupivacaine into the pulmonary tissue was investigated applying the multiple indicator dilution technique to isolated lungs perfused in the single-pass mode. The mean elimination time of model compounds for distribution into the intravascular space, 14C-insulin, and the total water space, 3H-water, were 68 and 75 s at a flow rate of 6 ml/min. The volume of distribution was 5.9 ml for inulin and 6.5 ml for water. The mean transit time for concomitantly injected bupivacaine was 221 s and the volume of distribution was 14.4 ml. The respective parameters of sham perfusions performed without an isolated organ were substantially lower, i.e. mean elimination time 50, 50 and 61 s and distribution volume 4.9, 5.0 and 6.1 ml for inulin, water and bupivacaine.2+ f1p4

Method for simultaneous determination of the distribution of capillary plasma flow and myocyte redox state (NADH-fluorescence) in the hypoperfused myocardium of the anesthetized rat.

A method is described which allows to observe the pattern of capillary plasma filling simultaneously with the redox state (NADH-fluorescence) of the myocytes in the hypoperfused myocardium. In anesthetized rats the coronary perfusion pressure was reduced to a defined level, the blood plasma labeled with dye-conjugated albumin and a myocardial biopsy-sampled. Freeze-substitution of histological sections allowed to detect the intravascular plasma label as well as the myocyte NADH-fluorescence on a microscopic level. It was found that areas showing increased cellular NADH-fluorescence did not arise in a distribution congruent with zones of failing capillary plasma flow in the hypoperfused myocardium.

Reconstruction of blood flow distribution in the rat kidney during postischemic renal failure.

Inner medullary blood flow has been found to remain nearly unchanged during postischemic renal failure, despite a severely disturbed perfusion in the outer medulla. In order to elucidate this discrepancy, rats were subjected to 1 h left renal artery occlusion and 1 h reflow. The blood plasma was then labeled by dye-conjugated globulin for 1 min. The in vivo indicator distribution was histologically analyzed, especially in the medullary vascular bundles. The filling there was observed along a section plane positioned through the inner stripe along the long and the short axis of the organ. Vessels centrally located within the bundles were more labeled than those in the periphery of the bundles. In addition, the degree of filling on the whole was almost twice as high in the tissue near the renal sinus as in the central area. At the same time, filling defects in the renal papilla were restricted mostly to the center of that tissue. The observations support the assumption that differences in blood flow obstruction exist within each bundle. They also show that perfusion defects of the outer medulla occur more readily in the center of the organ, thus allowing blood to enter the inner medulla via vascular bundles located marginally, adjacent to the renal sinus of the kidney.

Capillary filling kinetics in the rabbit heart during normoxemia and hypoxemia.

In experiments on anesthetized rabbits the kinetics of capillary plasma filling in the heart during normoxemia and hypoxemia were studied. Three gamma globulins originating from three different species were infused into the left atrium for various periods of time. The hearts were shock frozen, and the respective globulins were immunohistochemically identified in parallel sections. The anatomic capillary density was determined by staining the capillary basement membrane. During normoxemia 69 and 66% (subepicardium and subendocardium, respectively) of the capillaries were labeled within 2 s, 84 and 78% within 5 s, and 96 and 92% within 10 s. Labeling was complete after 20 s. Hypoxemia (arterial PO2 27 mmHg, 5 min) led to a significant acceleration of capillary filling kinetics: 93 and 95% within 2 s, 98 and 99% within 5 s, 100 and 99% within 10 s. During hypoxemic conditions the entire left coronary flow was found increased by a factor of 2.3. The data may best be explained by the fact that hypoxemia does not lead to mobilization of previously nonperfused capillaries but induces either an amplification of capillary flow velocities or an increased frequency of periods with high capillary blood flow.

Acute changes in microvascular blood flow distribution in the myocardium of the rat during partial occlusion of the right coronary artery; effects of dihydroergotamine.

Changes in blood flow during restricted right coronary perfusion were studied in anesthetized rats. By use of a carotid-coronary shunt system, coronary perfusion pressure could be reduced to 40 mm Hg, leading to a fall in flow from 0.9 ml/min to 0.3 ml/min. The perfusion pattern within the flow-restricted area was determined by labelling the blood plasma with fluoresceinisothiocyanate (FITC) globulin (demonstration of the entire vascular system) and lissamine-rhodamine B200 (RB200) globulin (demonstration of actually perfused myocardial capillaries). In histological sections, arterial ramifications were evaluated with respect to the arrival of RB200 in their branches. Large filling defects were observed when flow was obstructed. After 10s labelling, in ramifications with a feeding artery larger than 15 microns in diameter, 10.5% of the vessels displayed dye in only one of the branches, and 13.5% in neither of the two branches. For smaller ramifications (less than 8 microns), these values amounted to 17.5% and 41.5%, respectively. A similar pattern was observed after vascular labelling for 60 s. When dihydroergotamine (2.0 micrograms/kg i.v.) was applied one minute after onset of occlusion, the perfusion inhomogeneity was significantly reduced (labelling in one branch and in none of the two, respectively: greater than 15 microns: 60% and 10.0%; less than 8 microns: 13.5%, and 26%). It can therefore be concluded that dihydroergotamine reduces hypoperfusion-induced inhomogeneity in myocardial blood flow.

Increased accumulation of plasma albumin in the extracellular space of the heart during hypoxia.

The question which was investigated in this study is whether an augmented capillary protein permeability occurs during hypoxia, an effect which might worsen the supply conditions of the tissue during O2 deficiency. Anaesthetized and thoracotomized rats and mice received an i.v. injection of lissamine-rhodamine B200 (RB200)-conjugated albumin and were then ventilated with a gas mixture of 11 vol % O2 for 3 min. At the end of this period the heart was rapidly frozen and histological sections were subsequently scanned for changes in the distribution of labelled albumin. In the control hearts 4.6% (rats) and 4.5% (mice) of the microscopic fields showed penetration of labelled albumin into the extracellular space of the heart. Hypoxia, however, proved to induce an increased shift of plasma albumin into this space in localized areas with signs of increases in the extracellular volume in these areas. The changes in distribution were observed in 26.0 and 35.8% of fields scanned in the histological preparations of the hearts of rats and mice, respectively. Affected areas were found to be randomly distributed through all layers of the heart. The results show that localized accumulation of plasma albumin and edema formation is induced in the extracellular space of the myocardium by even moderate degrees of respiratory hypoxia.

Effects of diltiazem and allopurinol in postischemic microcirculatory changes in the rat kidney.

The influence of diltiazem and/or allopurinol on kidney microcirculation was studied in anaesthetized rats, which were subjected to 60 min unilateral renal ischemia followed by 60 min reflow. In histological sections capillary plasma flow patterns were determined based on the distribution of two different fluorochrome-labelled globulins administered i.v.. In the outer medulla (OM) of untreated postischemic kidneys labelling of the capillary network was greatly diminished. Tissue areas occupied by red blood cells increased 4-6 fold. During reperfusion massive penetration of red cells in the urine was demonstrated by the occurrence of hemoglobin in the urine. Maintenance of the rats on allopurinol-saturated drinking water for six days prior to the experiment (daily intake approximately 50 mg allopurinol/kg body wt) combined with the i.v. administration of diltiazem during the pre- and postischemic period (16 mg/kg body wt) resulted in an almost complete normalization of capillary plasma flow patterns in the OM. In this region tissue areas occupied by red blood cells were much lesser in extent than in the untreated controls. Furthermore, urine hemoglobin content after the combined drug regimen was largely decreased when compared to the untreated ischemic group. Effects of the treatment with either of the drugs alone were qualitatively similar, but significantly less pronounced. In conclusion, a synergistic effect of diltiazem and allopurinol in improving postischemic renal microcirculation is clearly evident, whereas no improvement in kidney function was demonstrable. This supports the hypothesis that disturbed microcirculation is not a prerequisite for the generation of the renal functional deterioration in the clamp-induced ischemia model in the rat.

Determination of capillary perfusion pattern in rat brain by timed plasma labeling.

The pattern of capillary perfusion was studied in the brain of anesthetized rats. Two plasma labels were used to demonstrate the density of capillaries perfused during a 10-min period [fluorescein isothiocyanate (FITC) globulin], as well as during a 10-, 3-, or 1-s period [lissamine-rhodamine B 200 (RB200) globulin, infused into the left heart chamber], respectively. A special biopsy cutting-freezing system was used to withdraw brain tissue via a cranial window for histological analysis of dye distribution at the end of the infusion period. Complete labeling of all capillaries was already found after 10 s of dye circulation. However, intra-arterial dye infusion for 3 and 1 s led to reduced filling of capillaries: cortex 86.6 +/- 5.2 and 6.8 +/- 1.8%, hippocampus 95.0 +/- 1.6 and 9.9 +/- 2.1%, and thalamus 97.9 +/- 1.0 and 11.7 +/- 1.8%, respectively. The period of 1 s was found to be the circulation time from left heart chamber to brain capillaries. It can thus be concluded that in the studied brain areas greater than 85% of capillaries are reached by a plasma flow within 2 s and that the remaining small fraction completely fills within 10 s.

Influence of diltiazem on postischemic microcirculation and function in the rat kidney.

Renal microcirculation and function were studied in the unilateral clamp-induced ischemia/reperfusion model in anesthetized rats. After 60-min reperfusion fluorochromelabeled globulin was injected i.v. allowing histological determination of capillary plasma flow patterns (CPFP). In the 60-min ischemia protocol the untreated group revealed poor capillary labeling in the outer medulla (OM), whereas cortical perfusion patterns were only slightly altered. Pre- and postischemic treatment with diltiazem led to significant improvement of CPFP in the OM: 4.9% of tissue areas were lying more than 60 microns from the next perfused capillary vs 70.2% after untreated ischemia. Postischemic treatment with diltiazem proved much less effective. Inulin clearance (CIn) amounted to less than 2% of baseline values irrespective of the treatment regimen. However, in the 30-min ischemia protocol, displaying normal CPFP, preservation of CIn was evident and most effective after pre- and postischemic diltiazem treatment (53% vs 8% after untreated ischemia). Measurements of tubular function, however, did not reveal any significant improvement after diltiazem treatment. This observation and the fact that the drugs has a vasodilating effect lend support to the view that the preservation of glomerular filtration rate (GFR) is most likely mediated by vascular mechanisms. In conclusion, in this experimental model diltiazem significantly reduced postischemic disturbances of renal microcirculation occurring after prolonged periods of ischemia and was clearly efficient in maintaining GFR after shorter ischemic episodes; however, tubular function was not preserved. Our results, as well as those of other authors, strongly suggest that diltiazem causes the aforementioned effects mainly by actions at the vascular site.

Hypoxia-induced acute changes in capillary and fiber density and capillary red cell distribution in the rat heart.

The influence of acute hypoxia (respiration gas 12%, 10%, and 8% O2 and asphyxia, respectively) on 1) the density of perfused capillaries and muscle fibers, and 2) the capillary red cell distribution was investigated in the left heart of anesthetized rats. To observe capillaries and fibers, fluorescein isothiocyanate-labeled (FITC)-gamma-globulin and lissamine-rhodamine-B200-labeled (RB200) myoglobin were injected intravenously as labels of the perfused intravasal and the extracellular space, respectively. The hypoxic conditions were induced subsequently and maintained for 3 minutes. After this period the heart was rapidly frozen for histological demonstration of the dyes. Ventilation with 12% or 10% O2 did not induce any changes in the density of perfused capillaries; however, 8% O2 in respiration gas did lead to a significant increase (capillaries/mm2: subepicardium, 4,180, controls, 3,620; subendocardium, 3,930, controls, 3,240). A similar increase was found in the asphyxia group (capillaries/mm2: subepicardium, 4,170; subendocardium, 3,700). The increases in the density of perfused capillaries were paralleled by rises in fiber density. This leads to the conclusion that the changes in capillary counts were caused by fiber elongation with a resultant decrease in intercapillary distances. This assumption was supported by observations that there were no signs of changes in ventricular segment length during respiration of 12% or 10% O2 but that an increase did occur with 8% oxygen and with asphyxia. Densities of perfused capillaries exactly coincided with anatomical densities (demonstrated by additional labeling of capillary basement membranes with isolectin B4) in normoxic and asphyctic hearts. The distribution of red cells in the capillaries, determined in histological sections, did not differ appreciably under hypoxia due to reduced O2 in respiration air (12%) or asphyxia. The results obtained indicate that 1) extreme hypoxic states cause the capillaries to move closer to each other due to elongation of myocardial fibers and 2) red cell distribution is not altered during these conditions.

Myocardial interstitial fibrosis in experimental uremia--implications for cardiac compliance.

Experimental uremia is known to cause cardiac hypertrophy. In the present study we examined the effect of uremia with or without concomitant treatment of hypertension by the converting enzyme Ramipril (125 micrograms/day) on micromorphometric indices of cardiac interstitium at the light microscopical and ultrastructural level. In male SD rats, 21 days of uremia caused an increase of total heart weight (1040 +/- 73 mg wet wt vs. 871 +/- 81 in controls, P less than 0.05) with an increase of both right and left ventricular weight. This was accompanied by reduction of capillary cross-sectional area despite unchanged capillary length. The volume density (cm3/cm3) of cardiomyocytes was unchanged (0.881 +/- 0.01 vs. 0.871 +/- 0.016 in controls), but volume density of interstitial tissue (excluding capillary lumen) was significantly increased (0.042 +/- 0.011 cm3 interstitial tissue/cm3 total heart tissue vs. 0.019 +/- 0.007 in controls). This was associated with signs of activation of interstitial cells, that is, increased volume of interstitial cell nuclei and interstitial cell cytoplasm. Concomitantly, a significant increase of volume density of non-cellular interstitial ground substance was found which was not normalized by antihypertensive treatment using Ramipril. After three months of uremia, electron microscopy showed collagen fiber deposition in the interstitium. Comparable interstitial fibrosis was not observed in hearts of rats with renovascular (one clip-two kidney) hypertension. It is concluded that uremia increases myocardial interstitial ground substance by mechanisms independent of hypertension. The data may be relevant for recent findings of diastolic heart malfunction secondary to impaired compliance in uremic patients.

Morphometric investigation of the microvascular system of pancreatic exocrine and endocrine tissue in the rat.

Morphometric data were obtained from the microvasculature in exocrine and endocrine tissue of the rat pancreas. Two groups of anesthetized rats (100 and 300 g body wt, respectively), received intravenous injections of fluorochrome-coupled globulins in order to label the entire vascular system. After circulation of fluorescein-isothiocyanate (FITC)-globulin through the vascular system for 30 min and lissamine rhodamine B 200 (RB 200)-globulin for 5 min, the pancreas was frozen rapidly. In frozen sections of the organ, both dyes showed the same intravascular distribution. The mean number of sectioned vascular elements was 970 +/- 40/mm2 in the exocrine parenchyma and 1430 +/- 60/mm2 in islet tissue. The cross-sectional area fraction of the microvascular system, which is equivalent to the intravascular volume fraction, amounted to 0.027 +/- 0.001 mm2/mm2 in the exocrine system and to 0.061 +/- 0.002 mm2/mm2 in the endocrine pancreas. The corresponding values for microvascular surface area (mm2/mm3) were 18.0 +/- 0.8 (exocrine tissue) and 34.2 +/- 2.0 (endocrine tissue). Mean diameters of vessels up to 10 microns in exocrine tissue amounted to 5.5 +/- 0.2 and 6.1 +/- 0.1 microns in exocrine and endocrine tissues, respectively; when all vessels up to 30 microns in diameter were considered, these values amounted to 5.7 +/- 0.2 and 6.7 +/- 0.2 microns, respectively. Especially in light of the fact that flow rate was observed to be much higher in islets than in acini, the present results support the existence of an insular microcirculatory system which is specialized in terms of its exchange capacity.

Inhomogenous capillary flow and its prevention by verapamil and hydralazine in the cardiomyopathic Syrian hamster.

There is clinical evidence that human dilated cardiomyopathy is related to microcirculatory disorders. We used an experimental preparation of the disease that consisted of a study of the microcirculation of 45 cardiomyopathic Syrian and 18 control hamsters with timed plasma staining. To investigate dynamic vascular disorders a double injection technique was used that permitted demonstration of all permanently and temporarily perfused capillaries in the same animal. The results showed a total capillary density of 3423 +/- 470 capillaries/mm2 in the cardiomyopathic hamster during the premyocytolic phase (30 days of age) and that of 3289 +/- 506 capillaries/mm2 during the myocytolytic phase (44 days). These values were not significantly different from those in the control group (3349 +/- 473 capillaries/mm2 at 30 days and 3383 +/- 556 capillaries/mm2 at 44 days). However, tissue areas with extended coronary transit times were detected only in the cardiomyopathic hamsters. These areas were of the same individual and cumulative size at 30 days (diameter approximately 200 micron, 4% of the tissue) as the myocytolytic zones at 44 days. In cardiomyopathic hamsters verapamil and hydralazine prevented both hypoperfusion and myocytolysis. The results favor the view that microcirculatory disorders generate tissue damage in the cardiomyopathic hamster and that these disorders can be prevented through treatment with the calcium antagonist verapamil or with the vasodilator hydralazine.

Capillary density and oxygen supply in human dilated cardiomyopathy.

Human hearts with dilated cardiomyopathy (DCM) exhibit a hypertrophy of the myocytes; consequently, the intercapillary distance increases, which may impede the diffusionable metabolic supply. Therefore in the following study the microcirculation of living human hearts with DCM, excised during cardiac transplantation, was investigated. The hearts were reperfused with a FITC-stained salt-solution, this allowed the precise detection of all plasma perfused capillaries. Thus, functional capillary density, capillary distribution and its effect on oxygen supply could be determined. In eight human hearts, the average functional capillary density amounted to 1245 +/- 345 capillaries/mm2, while 50% of the tissue was within 12 micron from the nearest capillary. However, a small portion of the tissue (1%) might become anoxic under the assumption of a simple oxygen diffusion model. The results favor the view that capillary density is low in human DCM and tissue is at the border of hypoxia.