Impaired microvascular responses to acute hyperglycemia in type I diabetic rats.

Abnormal reactivity of resistance vasculature may induce long-term alterations in regional hemodynamics, contributing to the pathogenesis of diabetic microangiopathy. The purpose of this study was to examine the responses of microvessels to a hyperglycemic episode aimed at mimicking a physiological stimulus such as the postprandial state. This study is the first to report the direct, in situ, visualization of this situation by intravital microscopy in the skeletal muscle of diabetic rat and is particularly interesting as it applies to an iterative, physiological stimulus. The study was conducted in 5-month-old rats, either nondiabetic (ND) or rendered diabetic (D) for 12 weeks (streptozotocin, 60 mg/kg, i.v.). Intravital microscopy was used to examine diameter and vasomotion changes in precapillary arterioles (< 20 microm) in the spinotrapezius muscle of fasted, anesthetized rats, before and up to 60 min after infusion of glucose or isotonic saline. After intravenous glucose infusion, a precapillary arteriolar vasoconstriction associated with an increase in the number of arterioles presenting vasomotion were seen in ND rats. In contrast, no modification in either parameter was observed in D rats. Our results indicate that, microvessels react to acute changes in the metabolic environment such as induced by elevation of plasma glucose. There was a complete loss of reactivity (vasoconstriction and vasomotion) of precapillary arterioles to superimposed hyperglycemia in D rats. According to the "hemodynamic hypothesis", this impaired vasoconstriction could result in hyperperfusion of microvessels and subsequent microvascular damages which might contribute to the development of diabetic microangiopathy.

Vascular permeability increase as induced by histamine or bradykinin is enhanced by advanced glycation endproducts (AGEs).

Advanced glycation endproducts (AGEs) may enhance vascular permeability in diabetic subjects. To test this hypothesis, AGEs were prepared in the presence of albumin (AGE-Alb). Control albumin (Alb) and AGE-Alb were then labeled with FITC (fluoresceinisothiocyanate) and injected i.v. into anesthetized hamsters at a dose of 7 mg/100 g B.W. Normal hamsters were given FITC-Alb or FITC-AGE-Alb and FITC-dextran. Vascular permeability changes were measured by direct intravital microscopy of the hamster cheek pouch preparations in fluorescent light and recorded as number of sites (=leaks) with extravasation of FITC-labeled albumin in postcapillary venules. No changes were seen during 1 hour after i.v. injection of FITC-Alb or FITC-AGE-Alb. Repeated local application of histamine 5 x 10(6) M or bradykinin 5 x 10(7) M to the cheek pouch for 5 min with 30-min intervals induced reversible increases in vascular permeability in all hamsters. Maximal number of leaks/cm2 before and at 30 and 60 min after FITC-Alb-injection and histamine application was 257 +/- 6 (SEM), 243 +/- 6 and 231 +/- 6 leaks/cm2 in the FITC-Alb-group and 258 + 6 (SEM), 302 +/- 12 and 316 +/- 11 leaks/cm2 in the FITCAGE-Alb-group, respectively, (P < 0.05 at 30 and 60 min). Similar results were seen with bradykinin. Our conclusions showed that i.v.-injected AGEs augmented the histamine- and bradykinin-induced increase in vascular permeability by 34% and 46%.

Hyperglycaemia modifies the reaction of microvessels to insulin in rat skeletal muscle.

The role played by glucose and/or insulin in local vascular regulation of tissue glucose uptake is largely unknown. Thus, the aim of this study was to examine microvascular changes induced either by hyperinsulinaemia alone or in combination with hyperglycaemia. The effects of insulin or glucose on the diameter and periodic vasomotion of precapillary arterioles (diameter < 20 microm) were determined by using the spinotrapezius muscle preparation in fasted, anaesthetized rats. Ten minutes after s.c. insulin administration, the blood insulin level was greatly increased whereas plasma glucose remained unchanged. This was associated with a marked and durable vasodilation of terminal arterioles without significant changes in vasomotion. When similar plasma insulin levels were attained by glucose infusion, tissue glucose uptake was increased in spite of a partial constriction and increased vasomotion of precapillary arterioles. Importantly, local tissue blood flow was not reduced despite the diminution in microvascular diameters. These results indicate that hyperinsulinaemia alone produces an increase in the diameter of terminal arterioles. This effect seems to be offset when the same level of hyperinsulinaemia is associated with hyperglycaemia (such as occurs postprandially), as illustrated by vasoconstriction of the muscle terminal arterioles. Our data suggest that the vasoconstriction of precapillary arterioles may be part of an active regulation for optimal glucose supply to the tissue in acute hyperglycaemic episodes. These data provide the first direct evidence that insulin and glucose can act as regulators of microflow in the skeletal muscle, as illustrated by changes in precapillary haemodynamics.

Diameters of acute proximal and distal deep venous thrombosis of the lower limbs.

BACKGROUND: Duplex ultrasonography of the veins in the diagnosis of deep venous thrombosis (DVT) can be interpreted in a semi-quantitative mode by measuring the antero-posterior (AP) diameter of the thrombus. We report the values of the diameters of thrombi and the factors influencing these values. Therefore we propose a quantitative definition for DVT in duplex ultrasonography. METHODS: 1,017 patients (3,767 thrombosed venous segments), referred to the Emergency Angiology Unit from January 1994 to September 1996. Characteristics: 55% F, 45% M; mean age 68+/-18 years; 624 proximal DVT (61%) and 393 distal DVT (39%). Measurement by venous echography of the antero-posterior diameters of thrombi at 25 predetermined sites in the area of the vena cava. RESULTS: (In mm, median, 10th and 90th percentiles after regrouping of contiguous anatomical sites not statistically different): thrombus in the common iliac veins and the inferior vena cava (12 mm, 7-17); external iliac and common femoral veins (9 mm, 5-14); superficial femoral, deep femoral and popliteal veins (6 mm, 4-10); calf veins (5 mm, 4-8). The age of the patients, their sex, body mass index (BMI), whether they were in- or outpatients or the laterality of the thrombus never significantly influenced its diameter. CONCLUSIONS: It is very unusual to observe a diameter of under 5 mm in cases of DVT. For clinical research therefore, we propose 5 mm as the minimum threshold value for this diagnosis. This value could be used in the venous echographic definition of DVT, as a criterion for inclusion in a therapeutic trial, for example, or in an epidemiological study.

In vivo effect of 8-epi-PGF2alpha on retinal circulation in diabetic and non-diabetic rats.

Retinal hemodynamic responses to a F2-isoprostane, 8-epi-PGF2alpha, were quantitated in vivo in non-diabetic and diabetic rats using a video fluorescein angiography system. Vascular diameters and retinal mean circulation time were determined before and after 5 microl intra-vitreous injection of 8-epi-PGF2alpha (10(-5) to 10(-3) M), 10(-4) M 8-epi-PGF2alpha, + 10(-3) M SQ29,548 or 10(-3) M LCB2853 (two inhibitors of TXA2 receptor), 10(4) M 9beta-PGF2alpha, or the carrier in non-diabetic animals. Diabetic rats received either 8-epi-PGF2alpha 10(-4) M, or the carrier. Compared to control animals, diabetic rats presented in the basal state a venous vasodilation (P<0.01), without modification of retinal mean circulation time or blood flow. After intravitreous injection of 8-epi-PGF2alpha, a significant arterial vasoconstriction was observed in control but not in diabetic animals. This vasoconstriction was concomitant with increased retinal mean circulation time in control but not in diabetic rats, inducing an impaired reduction of blood flow. No vasoconstriction was observed after injection of either the carrier, 9beta-PGF2alpha or the isoprostane associated to the inhibitors of TXA2 receptors. This is the first direct observation that the isoprostane 8-iso-PGF2alpha is a potent vasoconstricting agent in the retina. It occurs at the arterial but not venous level, and is likely mediated through a TXA2-like receptor. Differences observed between control and diabetic animals suggest altered adaptative mechanisms toward vasoconstrictor substances (such as isoprostanes) in diabetic rats.

Involvement of cell-cell interactions in the pathogenesis of diabetic retinopathy.

Retinopathy is a severely disabling complication of diabetes mellitus whose underlying mechanisms are still obscure. The key question is why retinal microvessels are so reactive to the diabetic environment, whereas other microvessels show no evidence of alteration. The answer could lie in the particular structure and location of retinal microvessels since they are composed of, and surrounded by, various types of cells, thereby favouring cell-cell interactions which occur between cells of the capillary wall itself but also with circulating blood cells and retinal neural cells. In the retinal capillary wall, pericytes are in close relation with underlying endothelial cells, and both cell types have close contacts with the capillary basement membrane. Adhesion molecules and cell surface glycoconjugates appear to be the main mediators of interactions between circulating blood cells and capillary endothelial cells, whereas growth factors seem to play a major role in interactions between glial and capillary wall cells in the retina. Biochemical dysfunctions observed in diabetes, such as glycation of proteins and enhanced oxidative stress, could modify these cell-cell and cell-matrix interactions, thereby disturbing the complex cellular organization in which retinal microvessels are embedded. The aim of this review was to provide an overall, nonexhaustive description of some types of cellular interactions that may underlie the pathogenic mechanisms involved in flow and growth changes leading to diabetic retinopathy.

[Chronic venous insufficiency 7 to 10 years after partial vena cava interruption with a clip]. / Insuffisance veineuse chronique 7 à 10 ans après interruption partielle de la veine cave inférieure par clip exocave.

In order to test the responsibility of inferior vena cava clips in post thrombotic venous disease, we performed a comparative retrospective study 7 to 10 years after vena cava interruption by clip. Patients were compared with patients matched for sex, age, and prior deep vein thrombosis (same period and same localisation) but without inferior vena cava partial interruption. The results show that 1) functional complaints were significantly higher in the vena cava clip group; 2) valvular incompetency, in the initially thrombosed leg, (tested by scanning duplex) was not different in the two groups: 3) inversely, on the other leg, valvular incompetency was greater in the vena cava clip group. Furthermore this valvular incompetency was principally located at a femoral level, suggesting that the vena cava clip may induce backward thrombosis; 4) complications were independent of vena cava thrombosis.

[Computerized medical register of venous thromboembolic disease at the Grenoble University Hospital Center: description and evaluation]. / Le registre médical informatisé de la maladie thrombo-embolique veineuse au Centre Hospitalier Universitaire de Grenoble: description et évaluation.

The number of vascular exams for venous thromboembolic disease increases dramatically in the vascular medicine unit at the Grenoble University Hospital (France). In order to improve the efficiency and the homogeneity of all the medical staff involved, a computerized register has been created. It automatically provides a letter for the prescriber of the consultation. This database, working on a computer network, has three main functions: office automation (medical folder, report), education, and clinical research. The office automation evaluation is performed after a 6 month experience, comparing 100 medical reports about venous thrombosis assisted by the computer to 100 medical reports written before the installation of the system. The introduction of digitized register is real, still this evaluation has induced some modification in the system in order to be more efficient.

Digitized nailfold capillaroscopy.

An image processing system was developed to quantify the morphometry of nailfold capillaroscopy. Image acquisition was performed with a macrophotographic technique, and images are digitized using a video camera and an image processing system. After an image segmentation, the microcomputer determines in an interactively defined window, the following parameters: capillary loop width and length, capillary surface area, distance from the tip of the capillary loop to the dermal edge, distance between two adjacent capillaries. Other parameters can be computed from these: linear density, density and dispersion index of the distance between two adjacent capillaries (variation coefficient). A validation study, comparing 20 capillary fields from healthy subjects and 19 capillary fields with "SD-pattern", provided from patients with systemic sclerosis or dermatomyositis, reveals significant differences of all these parameters between the two groups, consistent with the literature. This study also isolates two parameters which are the best predictors of the "SD-pattern": the mean capillary surface and the capillary density (capillaries/mm2). The morphometric parameters obtained through this system are suitable for evaluation of microangiopathy and should be evaluated for diagnosis and follow-up of vascular acrosyndromes, systemic sclerosis, Raynaud phenomenon and allied conditions in clinical conditions.

Two light attenuation models for automatic diameter measurement of the blood vessels.

The Lambert-Beer's law of the absorption of the light by blood in a vessel is used to model the light attenuation by a blood vessel that is transilluminated. Two models are used for an automatic vessel diameter determination for intravital microscopy. Some requirements for the photometric system have to be met in order to reduce errors due to light scattering. In these conditions, a videodensitometric pattern of the cross-section of the vessel can be fitted by the different models in order to obtain the diameter of the vessel. The first model proposed uses a uniformly distributed red blood cell column. A non-linear estimation of the diameter is done with the Levenberg-Marquardt method in 2 sec, using a regular PC386 microcomputer. The second one takes in account the presence of a plasma layer and computes the diameter of the red blood cell column and the diameter of the vessel in one minute. These models can be used for pharmacological studies or for a better understanding of the formation of a transilluminated intravital image. They can also be used for angiographic images.