Anatomy of the interstitial tissue.

Aspects on composition and function of the interstitial tissue have been given. The glycosaminoglycans of the interstitum have at physiological pH a net negative charge and are osmotically active. They restrict free diffussion through the interstitium. The ground substance phase can be further subdivided into a colloid-rich subphase and a colloid-poor subphase. The latter seems to constitute the true tissue fluid phase of the interstitium. The functional importance of the interstitium on exchange processes between the vascular and the cellular compartments is discussed. Changes in aggregation and hydration of the ground substance change the physico-chemical properties and the functional characteristics of the interstitium.     

The effect of glycosaminoglycans in the pulmonary interstitial fibrosis development]

The pulmonary interstitial fibrosis was caused by injecting Bleomycin into mouse trachea. After the injection, the volume of glycosaminoglycans (GAG) in bronchoalveolar lavage fluid and lung tissues was increased. The observation of histochemical stain and electron microscope showed that the distribution of GAG in lung tissues was varied at different time after the injection, and related to the volume of collagen proteins and the formation of pulmonary interstitial fibrosis.     

Prospects for cardioreparation.

The structure of the myocardium has 2 principal components, a myocytic compartment and a non-myocytic compartment that consists primarily of interstitial tissue. It appears that increased collagen production is mainly responsible for the functional consequences of structural remodelling. The concept of cardioreparation implies both a restoration of structural abnormalities and a return of cardiac function to or toward normal. In spontaneously hypertensive rats with left ventricular hypertrophy and adverse structural remodeling of the cardiac interstitium, angiotensin-converting enzyme inhibition has resulted in restoration of myocardial integrity and stiffness toward normal. Further research needs to be undertaken to identify the molecular mechanisms involved in the development of interstitial myocardial fibrosis, and reliable methods for assessing the interstitium and the changes that occur within it in clinical practice need to be developed.     

Extracellular matrix in normal and fibrotic human lungs

Polyclonal affinity-purified antibodies to human collagen types I, III, and IV, and laminin were used to compare the extracellular matrix (ECM) in 10 normal and 32 abnormal lungs by indirect immunofluorescence. In normal lungs, type IV collagen and laminin codistributed in a uniform linear pattern along the epithelial and endothelial basement membranes. Type III collagen was found within the alveolar septa and interstitium in an interrupted ribbonlike pattern and was aggregated at the entrance rings of the alveoli. Type I collagen was distributed irregularly within the alveolar wall and was less prominent than type III collagen. In patients with pulmonary disease not characterized by interstitial fibrosis (n = 15), the distribution of ECM components studied was essentially normal. In pulmonary disease in which interstitial fibrosis was the characteristic feature, such as idiopathic pulmonary fibrosis (IPF) and adult respiratory distress syndrome (ARDS) (n = 17), collagen types I and III accumulated in the expanded interstitium. Type III collagen was initially predominant in the thickened alveolar septa and interstitium, whereas type I collagen appeared to be the principal collagen at later stages in the disease course. The basement membrane was disrupted early in the disease course with invasion of the alveolar spaces by interstitial collagens similar in type to those present in the adjacent interstitium.     

Mechanical factors determining pulmonary interstitial fluid pressure

The pulmonary interstitium extends from sites adjacent to capillaries to the loose connective tissue around bronchi and large blood vessels. The interstitial fluid pressure in different parts of the interstitium depends primarily on the surface forces acting on adjacent structural members. At the alveolar level, the surface pressure is the alveolar gas pressure, which is modified by the alveolar surface tension in edematous lungs. In the perivascular interstitium around bronchi and large blood vessels, the surface pressure results from the balance between nonuniform stress in the parenchyma lying on one side of the interstitium and the elastic recoil of the vessel wall attached to the other side. Perivascular interstitial edema increases the interstitial fluid pressure by decreasing the nonuniform parenchymal stress and recoil of the vessel wall. A vertical gradient in interstitial pressure due to the interstitial fluid acting as a hydrostatic column is absent even in edematous excised lungs, because the surface forces determine the interstitial pressure locally and the resistance to interstitial fluid flow is relatively large. In the intact chest, vertical gradients in lung static recoil can result in significant vertical gradients in perivascular interstitial fluid pressure. During edema formation, the interstitial pressures are different in the two interstitial compartments, establishing a pressure gradient that tends to move fluid from the septal to perivascular interstitium.     

The effects of hyaluronidase on interstitial hydration, plasma protein exclusion, and microvascular permeability in the isolated perfused rat heart

Hyaluronic acid, a principal glycosaminoglycan of the cardiac interstitium, may have a role in interstitial hydration, interstitial plasma protein exclusion and microvascular transport process (Wiederhielm, 1976b). We have investigated whether hyaluronidase reduces myocardial hyaluronate concentrations and thereby alters these several physical aspects in the isolated rat heart. Studies were conducted in ischemic, as well as aerobic hearts because of the reported therapeutic efficacy of the enzyme in myocardial ischemia. Two hours of perfusion with hyaluronidase significantly reduced myocardial hyaluronate content. Additionally, hyaluronidase decreased interstitial volume of both aerobic and otherwise edematous ischemic hearts, and prevented ischemic induced increased coronary vascular resistance in ischemic hearts. However, hyaluronidase did not effect the albumin interstitial exclusion volume or microvascular albumin and sorbitol exchange in aerobic hearts. In ischemic hearts, the enzyme did not prevent nor enhance the increase in microvascular permeability which occurred. We conclude that hyaluronate is neither a determinant of interstitial protein exclusion nor microvascular permeability, but plays an important role in interstitial hydration.     

Fibrillar collagen and remodeling of dilated canine left ventricle

To test the hypothesis that in the failing volume-overloaded ventricle, the extracellular matrix and fibrillar collagen in particular are major determinants of the architectural remodeling of the myocardium, this histopathological study of the dilated, postmortem canine left ventricle secondary to rapid ventricular pacing or aortocaval fistula was undertaken. Using the picrosirius-polarization technique to enhance collagen birefringence, we sought to examine the structural integrity of the collagen matrix and interstitium. In the dilated failing ventricle secondary to rapid pacing, we found 1) interstitial edema and a disruption or disappearance of collagen fibers that were apparent within 6 hours of pacing, persisted for weeks, and subsequently were associated with muscle fiber disorganization within the endomyocardium, 2) interstitial fibrosis that was present in the midwall and epimyocardium with chronic pacing, and 3) an early remodeling of intramyocardial coronary arteries that included medial swelling with smooth muscle degeneration followed by proliferative lesions involving fibroblasts and a subsequent perivascular and medial fibrosis. Many of these findings were still evident 48 hours after pacing had been discontinued. In contrast, the collagen matrix and interstitium seen with ventricular dilatation secondary to the circulatory overload that accompanies an aortocaval fistula were indistinguishable from that in sham-operated controls. Thus, we conclude that unlike the chamber enlargement and preserved ventricular function that accompany an aortocaval fistula, ventricular dilatation and failure caused by rapid pacing are based on an architectural remodeling of the myocardium. This structural dilatation involves the extracellular matrix and interstitium and appears to be related to altered permeability of intramyocardial coronary arteries. The mechanism or mechanisms involved in the pathogenesis of myocardial remodeling with rapid ventricular pacing require further investigation.     

A role for hyaluronan in the preservation of interstitial structure

Hydraulic resistance of interstitium is of major importance in body fluid distribution. In the synovial lining it is vital for the retention of intra-articular fluid, and is attributed chiefly to the network of interstitial biopolymers occupying intercellular gaps in the tissue. Selective removal of synovial hyaluronan (HA) by protease-free hyaluronate lyase results in an almost 10x increase in synovial hydraulic permeability from 0.48 +/- 0.24 microL min(-1) cm H2O (control) to 4.56 +/- 0.40 microL min(-1) cm H2O (mean +/- SD, n = 6 rabbits, p < .001, t test) leading to the hypothesis that hyaluronan plays a major role in the organization of interstitial matrix structure. To test whether removal of hyaluronan causes significant changes in synovial ultrastructure, morphometry of hyaluronidase-treated synovium was carried out. Following hyaluronidase, the thickness of the synovial lining was reduced from 13.0 +/- 1.6 microm (control) to 10.6 +/- 1.6 microm (mean +/- SD throughout, n = 50 measurements per rabbit, 6 rabbits. p < .001, t test). This was accompanied by a significant reduction of synovial interstitial volume fraction from 76.2 +/- 20.6% (control) to 67.04 +/- 24.94% (p < .001, t test), and an increase in collagen bundle volume as a fraction of interstitial volume from 40.75 +/- 4.97% (control) tissue to 48.77 +/- 11.72% (p < .0001, t test). The findings indicate that the removal of hyaluronan chains leads to morphological disruption. Thus, hyaluronan chains play a major role in the organization of synovial structure. The observed morphological changes are insufficiently large to explain fully the great rise in hydraulic permeability observed on HA removal. The latter is likely to be due to disruption of tertiary architecture at the molecular organization level.     

Age-Related Changes in Albumin-Excluded Volume Fraction

The space available to large macromolecules, such as albumin and globulin, is less than the total interstitial fluid volume due to the dense matrix formed by the interstitial ground substance. Changes in excluded volume are likely to indicate changes in the composition of the matrix. Spragne-Dawley rats were anesthetized with sodium pentobarbital. Serum mesenteric tissue, and peritoneal fluid samples were obtained. Albumin contents were determined by microrod electrophoresis. Serum and mesenteric tissue chloride concentrations were measured by the coulometric-amperometric method. Serum and mesenteric tissue sample chloride concentrations were not significantly different, suggesting that this loose connective tissue is composed almost entirely of extracellular matrix. Matrix hydration decreased with a regression slope of -0.014 (μg tissue water/μg tissue dry wt)/10 days. Serum and tissue albumin concentrations decreased between 210 and 630 days of age. Mesenteric loose connective tissue albumin-excluded volume fraction increased by 80% over this age range. The increase could not be accounted for by dehydration alone, suggesting that the increase in excluded volume fraction for albumin is also due to changes in tissue glycosaminoglycans or collagen.     

Effect of heterogeneous vasculature on interstitial transport within a solid tumor

Novel strategies for cancer treatment involving macromolecular therapeutic agents have been recently developed and show promising results. Inadequate and heterogeneous uptake in tumor tissue has been shown to be a major obstacle for these compounds in clinical cancer therapy. Such distributions have been difficult to account for in predictive models. A three-dimensional computational model was developed to investigate the role of heterogeneous vasculature on interstitial transport within a murine sarcoma. The model accounts for extravasation and extracellular transport in a porous media. Spatial variation of fluid filtration rate per unit volume of tissue and vascular permeability were estimated from a dynamic contrast-enhanced (DCE)-MRI data set. Fluid filtration (L(p)S/V) and permeability (PS/V) maps were embedded in a model of tumor tissue and used to predict interstitial fluid pressure (IFP) and fluid flow. As in previous studies, pressure profiles were predicted to be elevated within the tumor. The model predicted boundary-dependent variation in outwardly directed interstitial velocity with lower velocities predicted near the skin boundary. Simulated tissue distribution of a macromolecular albumin tracer (MW approximately 60 kDa) was found to be heterogeneous with lower concentrations predicted in certain central regions. Simulated distributions of Gd-DTPA tracer (MW approximately 0.57 kDa) were less heterogeneous than albumin tracer. In sensitivity analysis, predicted tracer uptake was enhanced by increasing vascular leakiness. Increasing the interstitial hydraulic conductivity relative to the surrounding tissue reduced the overall drug uptake.     

Interstitial exclusion of albumin in rabbit lung measured with the continuous infusion method in combination with the wick technique

OBJECTIVE: To determine albumin exclusion from the pulmonary perivascular interstitium by using the continuous infusion methods coupled with direct samples of pulmonary interstitial fluid via the wick technique. METHODS: To evaluate extracellular albumin distribution volume, radioactive ((125)I) rabbit serum albumin (RSA) was delivered intravenously until reaching a steady-state tissue concentration. In anesthetized rabbits with ligated kidney pedicles, extracellular (V(x)) and intravascular (V(v)) fluid volumes were measured as the distribution volumes of (51)Cr-ethylenediaminetetraacetic a id and (131)I-RSA, respectively. Post mortem, lung samples and interstitial fluid collected via implanted wicks were assayed for isotope activity. The extravascular wick fluid equivalent albumin distribution volume (V(a,w)) was calculated assuming equal concentrations of (125)I-RSA in interstitial and wick fluid. RESULTS: The mean (+/-SE) V(x), V(v), and interstitial fluid volumes (V(i) = V(x) - V(v)) were 1896 +/- 61 (n = 8), 556.8 +/- 19, and 1329 +/- 73 microL/g of blood-free dry lung tissue weight, respectively. The mean albumin-excluded volume (V(e,a) = V(i) - V(a,w) and the excluded fraction (V(e,a)/V(i)) were 875.8 microL/g +/- 58 and 0.66 +/- 0.05, respectively. CONCLUSIONS: At variance with previous indirect reports, the present data indicate that normal pulmonary parenchyma displays a tight fibrous structure that is highly restrictive with respect to plasma protein distribution.     

Collagen network remodelling and diastolic stiffness of the rat left ventricle with pressure overload hypertrophy

This study had two objectives: (a) to determine the accumulation of collagen and its structural remodelling in the hypertrophied rat left ventricle after 4 and 8 weeks of abdominal aorta banding; and (b) to correlate these findings with the diastolic stress-strain relation of the intact myocardium. In comparison to age and sex matched controls, the collagen volume fraction of the hypertrophied myocardium after 4 and 8 weeks of aortic banding increased significantly from 3.5(SD1.0)% to 7.8(4.2)% and 6.2(2.0)% respectively. This accumulation of collagen, or fibrosis, occurred in the absence of myocyte necrosis. Scanning electron microscopy showed increased density and thickness of the collagen weave and tendons. At 4 weeks, light microscopy showed interstitial oedema and disrupted collagen fibrils. Left ventricular diastolic stress-strain relations of both pressure overload groups were significantly steeper than that of the control group. Thus the response of the interstitium to the hypertrophic process that accompanies abdominal aorta banding is a complex process that includes a structural remodelling of the fibrillar collagen matrix and the early appearance of interstitial oedema, each of which may contribute to a rise in the passive stiffness of the intact myocardium.     

Role of the interstitial matrix and lymphatic pump in regulation of transcapillary fluid balance.

Blood/tissue fluid balance is governed by forces generated within the capillary, interstitial, and lymphatic compartments. This paper focuses on the role of the extracellular matrix and myogenic lymph pump in automatic control of transcapillary fluid movement. The physicochemical properties of the extracellular matrix determine the pressure and compliance of the interstitial spaces. In addition, the dependence of interstitial protein exclusion on matrix hydration amplifies the extent of oncotic buffering induced by interstitial volume alterations. Distension of muscular lymph vessels elicits increases in contraction frequency, stroke volume, and lymph flow. Thus, the rate of lymphatic removal of interstitial water and protein is geared to the state of hydration of the interstitial matrix. These interstitial and lymphatic compensatory reactions are important components of the “margin of safety” against edema formation.     

Diastolic dysfunction in the elderly--the interstitial issue

Diastolic dysfunction is increasingly recognized as a cause of congestive heart failure. Meta-analyses of earlier studies of this disorder suggest that 40%–50% of patients with the congestive heart failure syndrome have preserved left ventricular systolic function, with current estimates ranging up to 74%. Among patients ≥65 years of age with congestive heart failure, 55% of all subjects and 67% of women had normal systolic function. Histopathologic evaluation reveals a maladaptive remodeling of the interstitium associated with aging, resulting in an increase in interstitial collagen content. The interstitium normally plays a critical role in the generation of early diastolic suction. When there is a significant enough increase in myocardial collagen volume fraction, with its increased viscoelastic burden, this normal early diastolic suction is compromised and diastolic pressures increase. Left ventricular diastolic dysfunction ensues. Neurohumoral abnormalities associated with diastolic dysfunction include activation of the renin-angiotensin-aldosterone system, including increased elaboration of myocardial aldosterone. This excess of aldosterone appears to play a major role in the development of myocardial fibrosis. Recent observations in animal models and humans have demonstrated regression of interstitial collagen volume fraction in response to inhibition of the renin-angiotensin-aldosterone system by angiotensin-converting enzyme inhibitors and aldosterone inhibition, with improvement in diastolic function. Therapeutic implications of these observations suggest targeting the maladaptive remodeling of the interstitium via inhibition of the renin-angiotensin-aldosterone system.     

Localization of Fibril/Microfibril and Basement Membrane Collagens in Diabetic Glomerulosclerosis in Type 2 Diabetes

Collagen is one of the major components of the extracellular matrices of the kidney. Basement membrane collagen, type IV collagen, is the major component in normal glomeruli. Fibril and interstitial collagen such as type III collagen, type V collagen, and type VI collagen are minor components of glomerular extracellular matrices and are localized mainly in the interstitium. Diabetic glomerulosclerosis is characterized by the expansion of the glomerular mesangial matrix as well as by thickening of the glomerular basement membrane. In order to clarify the roles of these various types of collagen in the development of diabetic glomerulosclerosis, immunohistochemical studies were perfomed in kidney specimens from patients with Type 2 diabetes. Early glomerulosclerosis is characterized by expansion of mesangial matrix with basement membrane collagen. However, in later stages glomerulosclerosis is characterized by an increase in the minor collagen components, such as type V and type VI collagen or collagens not normally present, such as type III collagen. Mesangial cells are known to synthesize all these types of collagen. In diabetes, phenotypic change in mesangial cells might produce excess amounts of fibril and interstitial collagen such as type III, type V, and type VI collagen, thus, leading to glomerulosclerosis.     

Wick sampling of interstitial fluid in rat skin: further analysis and modifications of the method

We compared modifications of the wick technique for analysis of interstitial fluid in rat subcutis. Nylon wicks were implanted for 60 min in back skin of rats after anesthesia with pentobarbital or after sacrifice by potassium chloride injection. Wicks were implanted dry or loaded with saline or varied dilutions of rat serum. Implantation of dry wicks and wicks loaded with diluted serum in living, anesthetized animals produced similar results; the protein concentration of wick fluid averaged about 60% that of the plasma protein concentration. The saline loaded wicks produced wick fluid with a lower protein concentration, average about 45% that of plasma protein concentration. The lower concentrations apparently resulted from simple dilution. Wick fluid sampled from dead animals had similar total protein concentrations, but in the dead animals there was a lower concentration of the large plasma proteins and a relatively higher concentration of the smaller proteins. Conclusions: Wick implantation in living animals causes a transitory inflammatory reaction and a decrease in the size selectivity of macromolecular sieving, but local osmotic forces bring about a concentration equilibrium with undisturbed interstitium. Implantation of dry wicks in subcutis either in vivo or post mortem provides a simple, direct method for sampling the total protein concentration and colloid osmotic pressure of interstitial fluid. Implantation of dry wicks postmortem permits measurement of individual component protein concentrations and evaluation of molecular selectivity between plasma and interstitium.     

慢性冬眠心肌的间质重塑

目的：观察慢性冬眠心肌（CHM）间质变化及其对心功能的影响。方法：对小型猪采用球囊扩张及内膜剥脱术,造成心脏左前降支中段狭窄、心肌慢性缺血,建立CHM模型。24只小型猪被分成：CHM组和假手术组,于模型建立后4周、12周终止实验。心脏切片以HE染色,透射电镜观察组织形态学;以苦昧酸天狼星红（PSR）染色．偏光镜观察间质胶原纤维类型和比例;以免疫组化法测定间质糖蛋白、纤维结合蛋白（FN）和骨桥蛋白（OPN）;以超声心动图观察左室收缩功能。结果：较之假手术组（1）CHM的间质空间扩大,成纤维细胞增多．胶原增生;（2）CHM的间质胶原容积分数（ICVF）、血管周围胶原容积分数（PCVF）及光密度积分（IOD）、FN和OPN均明显增加．并随时间延长而增加（P〈0．01）;（3）PSR染色偏光镜观察示CHM组I型胶原大量聚集,排列紊乱。Ⅲ型胶原少量,I／Ⅲ胶原比例增高;（4）CHM组的左室射血分数（LVEF）、左室短轴缩短率（LVFS）、室壁增厚率（％WT）显著降低（P〈0．01）;（5）胶原纤维含量与LVFS、LVEF和％WT呈高度负相关（r=-0．754～-0．872,P〈0．01）。结论：慢性冬眠心肌出现间质重塑。     

Effects of oestradiol-17 beta on testicular microcirculation in rats

The effect of oestradiol-17 beta on testicular microcirculation in intact and hypophysectomized rats was studied before and after treatment with human chorionic gonadotrophin (hCG). Treatment of intact rats with oestradiol-17 beta for 5 days did not influence vasomotion but decreased testicular interstitial fluid volume (IFV). Treatment of intact rats with 50 IU hCG 8 h before the experiment began induced an increase in testicular IFV, abolished vasomotion and increased the accumulation of polymorphonuclear leucocytes in the testicular venules and interstitium. These changes were unaffected by pretreatment with oestradiol-17 beta, despite the decreased testosterone production. However, pretreatment with oestradiol-17 beta potentiated the hCG-induced migration of polymorphonuclear leucocytes to the interstitium. The interstitial fluid volume and number of polymorphonuclear leucocytes in blood vessels were decreased in hypophysectomized rats, and vasomotion was abolished. Daily treatment with 5 IU hCG increased the IFV and the number of polymorphonuclear leucocytes in blood vessels, and preserved vasomotion. Treatment of hypophysectomized rats with oestradiol-17 beta decreased testosterone production but did not influence basal IFV, vasomotion or the changes in IFV and vasomotion induced by 5 IU hCG. The present study shows that the regulation of testicular vascular permeability and vasomotion may not be directly related to testicular steroidogenesis, and that oestrogens are probably not involved as a mediator of the hCG-induced changes in testicular microcirculation.     

The lung parenchyma--a dynamic matrix. J. Burns Amberson lecture

The matrix of the lung parenchyma is composed predominantly of collagen, elastin, glycosaminoglycans, and fibronectin. This presentation focuses on the newer insights into injury and repair of lung elastin and glycosaminoglycans. Elastin and glycosaminoglycans respond in characteristic patterns to destructive and proliferative forms of lung injury. Elastin degradation induced by elastases induces a prompt and marked response by elastin resynthesis in situ. The signal for the stimulus remains unknown and deserves to be understood. The measurement of elastin peptides in plasma, urine, or bronchoalveolar lavage fluid can provide an objective index of elastin degradation in disease. Elastin depletion may be augmented by factors that interfere with elastin resynthesis such as exposure to tobacco smoke. Glycosaminoglycans participate in similar fashion in many different forms of lung injury as an early response to injury, which may then determine the subsequent cellular processes of repair. Studies of injury and repair in organ systems, other than the lung, suggest a general role for glycosaminoglycans in interstitial tissue and repair. The mediators that alter matrix chemical structure and function could provide powerful instruments for controlling the process of tissue injury and repair in the lung.     

Age-related modifications of aorta and coronaries in the rabbit: a morphological and morphometrical assessment

Aging seems to be related to various vascular diseases, such as dissecting aneurysm and atherosclerosis. The nature of the relationship between aging and these vascular diseases has not been completely clarified. The goal of this study was to investigate, using morphological and morphometrical methods, the age related modifications of the arterial wall in rabbits of three different ages, evaluating separately two different vascular districts and the various aortic segments. Our results confirm that the most relevant age-related structural aortic changes were the increase of thickness, length, volume and diameter of the vessels, together with the development of an intimal thickening. The latter was diffuse in the aorta and focal in coronary vessels and it appears earlier in the aorta than in the coronaries, being absent in the coronaries of young rabbits. In addition, morphological and ultrastructural studies revealed the presence in aged rabbits of some marked intimal storage of a ground substance into intimal thickening of proximal aortic segments. Morphometric studies demonstrated an age-related decrease of aortic cellularity of tunica media and a parallel increase of the content of collagen and glycosaminoglycans, whereas elastin did not vary. The different relationships between cells and interstitial tissue occurring with aging are most probably a phenomenon of adaptation to the changing forces acting on the arterial wall and they might constitute the structural background of the increased arterial susceptibility to various noxae. Finally, the intimal storage of the ground substance, probably related to a functional disturbance of endothelium and or smooth muscle cells, may play an initiating role in atherogenesis.