The popliteofibular ligament. Rediscovery of a key element in posterolateral stability

We have recently become aware of a strong direct attachment of the popliteal tendon to the fibula. To investigate the importance of this attachment, we examined 20 cadaveric knees. The popliteofibular ligament was identified in all 20 knees. The cross-sectional area of the popliteofibular ligament was 6.9 +/- 2.1 mm2, compared with 7.2 +/- 2.7 mm2 for the lateral collateral ligament. Biomechanical testing of these structures, simulating a purely varus stress on the knee, revealed that the lateral collateral ligament always failed first, followed by the popliteofibular ligament, and then the muscle belly of the popliteus. The mean maximal force to failure of the popliteofibular ligament approached 425 N (range, 204 to 778), compared with 750 N (range, 317 to 1203) for the lateral collateral ligament. Our results indicate that the popliteofibular ligament contributes to posterolateral stability.

Theoretical modelling of the release rate of low-density lipoproteins and their breakdown products at arterial stenoses

Arterial stenoses and luminal-surface irregularities at anastomoses cause blood-flow disturbances with slow recirculation. The authors created a computer simulation to study the rates of the release into blood of atherogenic substances such as low-density lipoproteins and their breakdown products from within the arterial walls at stenoses. Finite-difference methods were used to solve the Navier-Stokes equations (in the form of stream function and vorticity function) and the steady-state mass transfer equation for bell-shaped stenoses with two different degrees of constriction. This simulation indicated that the efflux rates of lipids and their breakdown products from the vessel walls were suppressed in the region of disturbed flow, with slow circulation distal to stenoses. The lowest efflux rate was found at the point of flow separation, and this rate was much lower than rates in regions of undisturbed flow. Therefore, this mathematical model predicts that locally disturbed blood flow at arterial stenoses and arterial anastomoses is responsible for two distinct phenomena: first, it provides favourable conditions for lipid infiltration into vessel walls; and, second, it impairs the release into the blood of atherogenic substances accumulated in the vessel wall. Such mass transfer abnormalities may account for atherogenesis and the late failures of arterial reconstructions at these sites.

[Effect of Chinese herbs on the circadian rhythm of body temperature and heart rate in rabbits with hypothyroidism (yang deficiency)]

The rectal temperature (Tr) and heart rate (HR) of three groups of New Zealand white rabbits, i. e. thyroidectomized (G1), thyroidectomized and treated with Chinese herbs (a decoction composed of tonifying kidney-yang herbs) (G2) and pseudothyroidectomized for control (G3), were observed dynamically for 26 hours. The results indicated that the Tr and HR in G1 were decreased, and the circadian rhythms of the Tr and HR disordered significantly, while these changes in G2 were corrected obviously.

[A study on the mechanism of severe hypoxemia associated with acute unilateral atelectasis in dogs]

OBJECTIVE

To study the mechanism of severe hypoxemia associated with acute unilateral atelectasis (AUA).

METHODS

Six dogs with acute left side atelectasis were studied during the period of rest and exercise. The pulmonary shunt and PaO2 were measured at different levels of ventilation of right lung.

RESULTS

After the left side ateloctasis during resting condition, the right lung could compensate to produce only mild hypoxemia (PaO2 9 kPa). But with further increased ventilation by exercise the shunt increased (from 19% to 29%) and led to severe hypoxemia (PaO2 8 kPa). When an artificial pneumothorax was instituted on the left lung, the shunt decreased (from 29% to 18%) and PaO2 increased (from 8 kPa to 9 kPa).

CONCLUSIONS

After AUA, whether severe hypoxemia would occur is determined by the volume of ventilation of the normal side lung. The excess increase of ventilation of the normal side lung by any reason may result in severe hypoxemia.

Gross, histological, and microvascular anatomy and biomechanical testing of the spring ligament complex

In recent years there has been an increased interest in the treatment of acquired pes planus. The breakdown of the medial longitudinal arch is most often seen at the talonaviculocalcaneal articulation. This suggests a relationship between the ligamentous complex at this articulation and acquired pes planus. This study was undertaken to gain a better understanding of the gross, histologic, and microvascular anatomy, as well as the biomechanics of the ligamentous structures surrounding the talonaviculocalcaneal articulation. Cadaver dissections of 38 fresh-frozen feet were performed. Detailed descriptions of the gross anatomy of the superomedial calcaneonavicular ligament, inferior calcaneonavicular ligament, and the superficial deltoid ligament were recorded. Their relationships to the posterior tibialis tendon and to the bones of the talonaviculocalcaneal articulation are described. The histology and microvascularity of these structures were also studied. Preliminary biomechanical testing was performed. It was found there are two definitive anatomic structures that are commonly called the spring ligament: the superomedial calcaneonavicular ligament (SMCN) and the inferior calcaneonavicular ligament (ICN). The SMCN ligament was found to have histologic properties that suggest significant load bearing. The histology of the ICN ligament suggests a pure tensile load function. The deltoid ligament and the posterior tibialis tendon had direct attachments to the SMCN ligament in all specimens. An articular facet composed of fibrocartilage was found in each SMCN ligament specimen. The microvascular structures showed an avascular articular facet present in the ligament. The biomechanical testing showed that the SMCN ligament and ICN ligament had strength similar to ankle ligaments. This study suggests this "spring ligament complex" has more of a "sling" function for the talar head. It is hoped that the better understanding of this region will add to our understanding of the etiology of pes planus and possible treatment alternatives.

[Changes in calcium uptake and Ca(2+)-ATPase activity of cardiac sarcoplasmic reticulum in rat associated with hypoxia of various degrees]

Two groups of Wistar rats were exposed to hypoxia at 5000 to 8000 m high above the sea level in a hypobaric chamber for 7 days. The effects of hypoxia on left cardiac function, sarcoplasmic reticulum (SR) Ca2+ ATPase activity and SR calcium uptake were observed. The results indicated that the left ventricular function exposed to hypoxia at 5000 m was much higher than that at 8000 m. Calcium uptake and Ca2+ ATPase activity of the exposed groups decreased significantly compared with those of the control group, but they were much higher in the exposed group at 5000 m than at 8000 m. These results suggest that the changes in calcium uptake and Ca2+ ATPase activity of SR may be one of the important biochemical indicators for cardiac function alterations associated with hypoxia.

ErbB-2, a c-erbB-2-coded protein, is expressed in metastatic cells of adenocarcinoma of endometrium, cervix and ovaries

Ten cases of gynecologic malignancies, including three endometrial, two ovarian and four cervical carcinomas, were studied for the expression of a 185 kDa protein (ErbB-2), coded by a proto-oncogene, c-erbB-2, in primary lesions as well as in metastatic lesions. Positive immunoreactivity was observed in all primary adenocarcinomas but not from squamous cell carcinomas. Many adenocarcinoma cells in distant metastatic sites or in tertiary lymph nodes were strongly stained for ErbB-2. These metastatic cells also showed an expression of proliferating cell nuclear antigen (PCNA). Detection of ErbB-2 mRNA by a reverse-transcription polymerase chain reaction showed that the transcription occurred exclusively in adenocarcinomas. To our knowledge, this is the first report demonstrating ErbB-2 expression in distant metastatic lesions of gynecologic cancers.

Carbodiimide cross-linked gelatin: a new coating for porous polyester arterial prostheses

The performance of a polyester arterial prosthesis impregnated with gelatin and cross-linked with carbodiimide (Uni-graft) was compared with its porous parent graft (Protegraft) using a canine thoraco-abdominal bypass model. The grafts were investigated in terms of their handling characteristics, imperviousness at implantation, surface thrombogenicity and healing behaviour. Prostheses 30 cm in length were implanted for the following periods: 4, 24 and 48 h, 1, 2 and 4 weeks, 2, 3, 4, 5 and 6 months. Both types of graft had good handling characteristics. The ready-to-use impregnated graft provided satisfactory haemostasis at implantation with no blood permeating through the wall after flow was restored. Both grafts exhibited low surface thrombogenicity, as determined by the uptake of labelled fibrin and platelets, and the healing sequence of the impregnated graft after resorption of the gelatin was equivalent to that of the preclotted control. Biodegradation of the gelatin was complete within 1 month of implantation with the subsequent development of a collagenous internal capsule at both anastomoses. Endothelial cells were observed between 4 and 6 months, but were confined to small islets distributed along the luminal surface. The prostacyclin/thromboxane A2 (PGI2/TXA2) ratio, which gives an indication of the level of endothelial cell activity, was greater than 1.0 after 1 week of implantation for the control graft. For the impregnated graft it reached 1.0 only after 3 months of implantation, but remained above 1.0 for periods of up to 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser Raman spectrometry study on experimental galactose-induced cataract

PURPOSE

To observe the dynamic changes of hydration in galactose induced cataract.

METHODS

Two groups of Wistar rats were used in the experiment. There were 12 rats in the experimental group, which were fed diet of 50% D-Galactose standard feed; while the control group had 8 rats fed standard feed. Their other living conditions were the same. At desired time periods, two Wistar rats fed galactose and one normal control were selected and killed 20 minutes before the instrument examination respectively, then, their lenses were removed from the orbs by a posterior approach. The cleaned fresh lens was placed in a quartz cuvette with Tris buffered balanced salt solution containing 5.5 mmol/L glucose. The quartz cuvette was placed on the stage of the Spectrometer. The laser beam was focused at the lens nuclear from the bottom of the cuvette and the scattered light was collected at 90 degrees to the incident beam.

RESULTS

Raman spectroscopy showed that (1) during the formation of galactose cataract, the water signal (at 3390cm-1) increased obviously, and the ratio of I3390/I2935 increased from 0.31 (3 days) to 2.26 (17 days), which is correlated with the imbibition of water in the lens nuclear; (2) the hydration of lens nuclear could be divided into two phases. The ratio I3390/I2935 was increased slowly and steadily by 11 days after galactose feeding. Then, the ratio turned to increase quite fast till 17 days.

CONCLUSION

The hydration of nuclear is changed simultaneously with the formation of cataract. The hydration of nuclear is mainly due to the imbalance of Na+/K+.

The gelweave polyester arterial prosthesis

OBJECTIVE

To determine the effect of the gelatin coating on the efficacy of Gelweave, a new gelatin-sealed woven polyester graft material, as an arterial prosthesis.

DESIGN

In-vitro and in-vivo studies of the prosthesis.

SETTING

A laboratory of experimental surgery in a university teaching institution.

SUBJECTS

After in-vitro testing of the material, eight dogs were subjected to a series of in-vivo tests to evaluate the properties of Gelweave in comparison with its unsealed precursor and a commerically available collagen-coated woven polyester prosthesis.

INTERVENTION

Implantation of the prosthesis as a thoracoabdominal bypass for prescheduled periods ranging from 4 hours to 6 months.

MAIN OUTCOME MEASURES

Physical and chemical properties of the virgin prosthesis compared with the other two prostheses, effects of the gelatin-sealed prosthesis on healing, the hematologic characteristics of the dogs before operation and at sacrifice, microscopic studies, fibrin and platelet uptakes, prostaglandin secretion, and properties of the Gelweave grafts removed at varying periods after implantation.

RESULTS

The gelatin sealant in the Gelweave prosthesis effectively reduced the water permeability of the new prototype to zero. Neither blood loss at implantation nor infection during the postimplantation period was observed. The gelatin impregnation did not cause any adverse response in the dogs and was completely lysed within 2 weeks, thus allowing encapsulation and graft healing to progress satisfactorily. After 2 weeks, the prostacyclin:thromboxane ratio was greater than 1.0, whereas the fibrin and platelet uptakes on the luminal surface of the Gelweave grafts remained low, regardless of the period of implantation. Analysis of the explanted grafts confirmed that this gelatin-sealed prototype prosthesis healed satisfactorily and no adverse biologic response occurred as a result of the gelatin coating. It maintained its biostability during 6 months in situ.

CONCLUSION

The new Gelweave arterial prosthesis is ready for clinical use as a thoracic and abdominal vascular substitute.

Renal vasodilation with L-arginine. Effects of dietary salt

Infusion of L-arginine, the substrate for nitric oxide synthase, causes renal vasodilation. Since dietary salt restriction blunts the renal vasoconstrictor response to inhibition of nitric oxide synthase, we investigated the hypothesis that dietary salt intake determines the renal vascular response to L-arginine. Bolus intravenous doses of L-arginine given to anesthetized Sprague-Dawley rats caused dose-dependent increases in renal blood flow and decreases in renal vascular resistance, whereas D-arginine was not effective. The response to L-arginine was prevented by pretreatment with NG-nitro-L-arginine methyl ester. Compared with rats adapted to a high salt diet, those adapted to a low salt diet were more sensitive to the reductions in blood pressure and renal vascular resistance (threshold dose of L-arginine for renal vascular resistance: low salt, 2.9 +/- 0.9 mumol . kg-1 versus high salt, 20.0 +/- 6.2; P < .025), but the maximal changes in renal vascular resistance were similar (low salt, -43 +/- 5% versus high salt, -34 +/- 5%; P = NS). Bolus doses of L-glycine also caused dose-dependent renal vasodilation, but the renal vasodilator responses were not affected by salt intake. Preinfusion of L-arginine augmented the renal vasoconstrictor response to NG-nitro-L-arginine methyl ester in low salt but not high salt rats; after L-arginine dietary salt no longer significantly affected the renal vasoconstrictor response to NG-nitro-L-arginine methyl ester. In conclusion, renal vasodilation is more sensitive to L-arginine during salt restriction. This effect is specific for L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Children's development effecting blood oxygen desaturation following apnea

One hundred and fifty-six children aged from 4 months to 12 years undergoing elective plastic surgery were included in this study. All children were ASA physical status I, under normal development, ranging from 64 to 140 cm in body height and from 6.0 to 41.0 kg in body weight. Following 2-minute preoxygenation, the time when SpO2 dropped to 95% and 90% in apneic period had a close correlation with age, weight and height of children by means of linear and non-linear regression analysis. The smaller the children's weight, the higher the incidence of severe arterial desaturation after reinstitution of manual ventilation with 100% oxygen at SpO2 of 90%. It is suggested that younger children are more susceptible to hypoxemia than older ones during apnea and provided no problem existing other than oxygen delivery, an SpO2 of 95% might be the safe limitation of apnea in pediatric anesthesia induction.

Endothelial barrier resistance in multiple organs after septic and nonseptic challenges in the rat

Local variations in endothelial permeability, hypothesized to play a role in the development of multiple-organ injury, were measured by 125I-labeled human serum albumin flux and leakage index in rats with a variety of challenges. The albumin flux significantly increased in the peritoneum, pancreas, stomach, and liver in acute pancreatitis; in the peritoneum and liver in abdominal sepsis; in the spleen, proximal small intestine, colon, liver, lungs, heart, and muscle in bacteremia; in the kidneys, liver, lungs, heart, brain, and muscle in endotoxemia; and in the peritoneum, proximal small intestine, colon, kidneys, liver, and heart after bradykinin administration. A redistribution of the tissue blood content, measured by 51Cr-labeled red blood cells, was noted. An increased albumin leakage index, assaying endothelial permeability considering local hemodynamic alterations, was noted in various organs in the different experimental groups. Thus septic and nonseptic challenges induce endothelial barrier injury. The endothelial resistance appears to be organ and/or tissue dependent and associated with a redistribution of blood.

[Structural changes of extra pulmonary artery and pulmonary arterioles of rats during chronic hypoxia and their significance]

The structural changes of extra pulmonary artery (PA) and pulmonary arterioles and their effects on the pulmonary arterial pressure (PAP) under chronically hypobaric hypoxia (5000 m) were studied. The results showed that (1) The endothelial edema of extra PA and pulmonary arterioles gradually reduced and the endothelial proliferation took place along with the prolongation of hypoxic exposure followed by the recovery of endothelium-dependent relaxation evoked by Ach from depression. This result suggested that the release of E-DRFs from endothelium increased with the structural changes of endothelium in the course of hypoxic exposure, which may be a reason why PAP did not increase any more after 21 to 40 of days exposure. However, the strengthened contraction of PA, the proliferation of cells on the vascular wall, and the muscularity of pulmonary arterioles being related to the hypoxic endothelium may produce a negative effect on decrease of PAP, resulting in persistently higher PAP. (2) The structural changes of pulmonary arteriole endothelium were more severe than those of extra PA endothelium, indicating that pulmonary arterioles might be more sensitive to the stimulation of hypoxia.

Evaluating the Dialine vascular prosthesis knitted from an alternative source of polyester yarns

The sudden and unilateral decision by E. I. DuPont de Nemours & Co., Inc., to withdraw its polymers for use in implantable devices has presented the medical device industry with an immediate and serious challenge to find alternative sources of biomaterials. In France, the company Cardial S.A. has already taken steps to find an alternative polyester yarn to replace Dacron by developing a new arterial prosthesis knitted from polyester yarns supplied by Rhône-Poulenc Fibres. This article describes an in vitro and in vivo study of this French device, called the Dialine prosthesis, with a view to determining its relative performance compared to current American and British prostheses, which rely on DuPont's Dacron yarn. In addition to analyses of the morphology and textile structure, and measurements of its physical and chemical properties, the Dialine graft was implanted as a thoracoabdominal bypass in dogs for periods ranging from 4 h to 6 months. In addition to our pathologic and histologic observations, we cleaned and evaluated the explanted prostheses for in vivo changes in dimensions, strength, and crystalline microstructure. The Dialine graft was found to differ structurally from other polyester prostheses because it is warp-knitted from a mixture of flat and texturized yarns with finer filaments. Its denser structure has a lower water permeability, greater flexibility and ease of handling, satisfactory strength, and dimensional stability, and it presents different textures on its luminal and external surfaces. The in vivo trial demonstrated that it has excellent biocompatibility and biostability over 6 months. With no thrombi observed on the luminal surface after 3 months, it has a faster rate of healing, generates compact external and internal capsules with a thinner neointima, and has an overall milder inflammatory response than is normally observed with Dacron-based prostheses.

Longitudinal forces acting at side-to-end and end-to-side anastomoses when a knitted polyester arterial prosthesis is implanted in the dog

In a previous study, which investigated the tensions at the proximal and distal end-to-end anastomoses of a vascular prosthesis, no significant differences were found in the longitudinal forces between the two anastomotic sites after different periods of implantation. The present follow-up study was devised to study the longitudinal forces at a proximal side-to-end and a distal end-to-side anastomosis using a warp knitted polyester prosthesis implanted as a canine thorocoabdominal bypass. The external surface of the prosthesis contained a specially printed "tension indicator" design, which enabled changes in length to be assessed photographically at the two anastomoses at the time of implantation and at sacrifice. The longitudinal force at each site was then calculated using a relationship obtained experimentally between the total longitudinal force and the changes in length of the virgin graft in vitro. The in vitro measurements on the prosthesis were performed using a computer-controlled laser calibration system. Although the results showed a tendency toward a gradual loss in longitudinal force at both anastomoses over 7 months in situ, statistical analysis showed no significant difference in the longitudinal force at the two anastomotic sites after any period of implantation. Histopathological and textile analysis also showed that the characteristics of the prostheses were similar at both anastomotic sites. This does not mean, however, that the intramural stress concentrations experienced by the two sites were the same. While comparing the level of the longitudinal forces measured in this study with those observed in the previous thoracic aorta study using end-to-end anastomoses, no significant differences were observed due to the different types of anastomoses. It would appear that the longitudinal force is not one of the main etiological factors that cause the formation and localization of anastomotic failure.

Strategies for an anterior capsular shift of the shoulder. A biomechanical comparison

We evaluated the effect of two different anterior capsular shift strategies on load-induced multidirectional glenohumeral motion. Nine cadaveric shoulders were tested on a special test apparatus in which three motions were constrained but which allowed simultaneous measurement of three translations: anteroposterior, mediolateral, and superoinferior. A simulated Bankart lesion was created by detaching the inferior glenohumeral ligament and labrum from the anterior glenoid from 5 mm superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The two types of medial-based anterior capsular shifts were performed sequentially using fixation via a transglenoid drill hole and No. 2 suture. One shift medialized the anterior capsule on the glenoid by 5 mm; the other one shifted the anterior capsule 5 mm superior on the anterior glenoid. Biomechanical testing was done in two positions of humeral elevation in the scapular plane, three positions of humeral rotation, and with an externally applied joint compression load of 22 N. Glenohumeral motion was measured in the intact state, after creation of the simulated Bankart lesion, and after each of the two anterior capsular shifts. Both the superior and medial shifts of the capsule decreased anterior glenohumeral translation to equivalent extents. For posterior and inferior translation at 45 degrees elevation, the superior shift significantly decreased translation to a greater extent than did the medial shift.

[Estramustine phosphate, estrogen conjugated with nitrogen mustard inhibits the growth of endometrial cancer cells in vitro]

Estra-1,3,5 (10)-triene-3,17-diol (17 beta)-, 3-[bis(2-chloroethyl) carbamate] (Estramustine EM) was tested for its anticancer effect on human endometrial cancer cell lines: Ishikawa and its estrogen (E) independent sub-clone EIIL (Estrogen Independent Ishikawa Line). The results showed: (1) EM inhibited growth of both cell lines in a dose dependent manner giving ID50 for Ishikawa as 12 microM and for EIIL as 65 microM. (2) The addition of EM to the culture medium caused cell detachment and death associated with a breakdown of DNA to approximately 90 base pair fragments. (3) Reverse transcription-polymerase chain reaction to examine expressions of c-erbB-2, nidogen and fas showed that EM completely abolished fas expression and resulted in a 40% decrease in nidogen expression in Ishikawa but not in EIIL. No change was seen in c-erbB-2 expression. The present data indicate that the E component of EM does not stimulate the growth of Ishikawa or EIIL. Since the growth of both cell lines was inhibited but apparently in an E receptor (ER) dependent manner, EM may be of value in an adjuvant therapy for endometrial cancer, especially an ER positive one.

Effects of caffeine or EDTA post-treatment on EMS mutagenesis in soybean

Seeds of soybean cultivar LD4 were mutagenically treated with EMS (0.3, 0.5, 0.6, 0.9, 1.5 and 1.8%) for 3 h only or plus caffeine (50 mM) or EDTA (1 mM) post-treatment for 5 h. The experimental results indicated that: (1) of the different concentrations of EMS treatment, the M2 mutation frequency induced with 0.6% EMS was the highest (9.7%). When the EMS concentration was over 0.9%, the mutation frequency decreased rapidly. (2) Of the EMS treatments plus caffeine or EDTA post-treatment, the mutagenic effect of 0.6% EMS was the best for inducing morphological variations. Caffeine post-treatment decreased notably the mutation frequency of EMS treatment; when concentrations of EMS were very high (1.5% and 1.8%), mutation frequencies of EDTA post-treatment were still 5.0% and 4.88%, but no mutants were found in EMS treatment or plus caffeine post-treatment. (3) In the M2 mutation spectrum, 11 kinds of mutant types were observed in EMS treatment or plus caffeine or EDTA post-treatment. Relative frequencies of some mutant types (growth period, plant height, grain size, leaf shape and sterility, etc.) were similar among the three treatments, but EDTA post-treatment could change the relative frequencies of yield characteristics (number of pods and grains, grain weight/plant) induced by EMS treatment only.

[Establishment of metastatic sub-clone from estrogen independent Ishikawa cells and its characterization in vitro and in vivo]

An estrogen (E) independent sub-clone (EIIL) was separated from a human endometrial carcinoma cell line, Ishikawa, by culturing the wild type under an E free condition for 350 days. The cells were then implanted into nude mice subcutaneously and tumors allowed to develop for 35 days. The primary lesions were then excised to stimulate recurrence. One animal developed recurrence with multiple distant metastases. The primary tumor and metastatic tumors from the animal were studied for ErbB-2 expression by immunohystochemical techniques or by a reverse transcription followed by polymerase chain reaction (RT-PCR). Expressions of epidermal growth factor (EGF) receptors, aromatase, nidogen, E receptors, hepatocyte growth factors (HGF) and beta-actin were also examined. The results showed that metastatic lesions expressed high levels of ErbB-2, nidogen and aromatase but unchanged levels of EGF receptors and HGF. The metastatic lesions expressed one third of the E receptors which were detected in the EIIL in vitro. These observations suggest that a decrease in ER along with increased expression of nidogen and aromatase is associated with the process of metastasis and the model appears to be of value in studying the process of the acquisition of a metastatic phenotype.

Localization of atherosclerosis in arterial junctions. Concentration distribution of low density lipoproteins at the luminal surface in regions of disturbed flow

To investigate the role of fluid mechanical factors in atherogenesis and anastomotic intimal hyperplasia, the effect of blood flow on the transfer of low density lipoproteins from flowing blood to the luminal surface was studied theoretically using a two dimensional T-junction model. The flow fields in the junction were obtained by solving the Navier-Stokes equations numerically and the concentration distribution of low density lipoproteins at the luminal surface was determined using a finite difference analysis. The transfer of low density lipoproteins from flowing blood to the surface of the vessel wall was greatly enhanced in the two regions of disturbed flow, one in the main vessel, the other in the subsidiary vessel. The highest concentration of low density lipoproteins on the inner surface of the vessel wall was predicted to occur in the areas of the reattachment points. The slower the recirculation flow, the higher the lipid accumulation at the luminal surface in the disturbed flow regions and the wider the highly concentrated low density lipoprotein area. In summary, the authors' mathematical model predicts that locally disturbed blood flows at arterial bifurcations and surgically created junctions provide favorable conditions for the accumulation of atherogenic substances at the luminal surface, thus increasing the potential for lipid infiltration into the vessel wall.

Validation of miniature ultrasonic transit-time flow probes for measurement of renal blood flow in rats

This study validates the accuracy of miniature ultrasonic transit-time flow probes for measuring renal blood flow (RBF) in the rat. Probes for 1-mm and 2-mm vessels were calibrated ex vivo using excised arteries at varying flow rates and hematocrit (Hct). Correlation between measured and true flow rates for the 2-mm probe were identical (r = 1.0) at both normal and subnormal Hct values. Correlation for the 1-mm probe was high (r = 0.994) at normal Hct, but varied at both high flow rates and subnormal Hct values. In vivo correlation of RBF measurements using the 1-mm probe with the clearance and extraction of p-aminohippuric acid showed a high correlation (r = 0.84; n = 72, P < 0.0001) over a wide range of flow rates (0.5-21 ml/min) and Hct (36-74%). Zero flow levels remained steady, averaging -0.2 +/- 0.2 ml/min during occlusion in the living animal and -0.1 +/- 0.3 ml/min after exsanguination. This study shows that the ultrasonic transit-time flowmeter (1-mm and 2-mm probes) is a reasonably accurate and reliable method with which to measure RBF in the anesthetized, acute-instrumented rat.

Luminal surface concentration of lipoprotein (LDL) and its effect on the wall uptake of cholesterol by canine carotid arteries

PURPOSE

The effect of near-wall blood flow velocity and plasma filtration velocity across the arterial wall on luminal surface concentration of low-density lipoproteins (LDL) and the uptake of tritium-cholesterol were investigated.

METHODS

A numeric analysis of LDL transport in steady flow, over the range of physiologically relevant flow rates, predicted a surface concentration of LDL of 4% to 16% greater than that in the bulk flow. The LDL surface concentration increased linearly with filtration velocity and inversely with wall shear rate.

RESULTS

These were validated experimentally in canine carotid arteries. When the transmural pressure was increased from 100 to 200 mm Hg, the filtration velocity increased from 5.13 x 10(-6) cm/sec to 8.41 x 10(-6) cm/sec, whereas the normalized uptake rate of tritium-cholesterol increased from 3.58 x 10(-4) cm/hour to 7.36 x 10(-4) cm/hour.

CONCLUSION

These results indicate that lipids accumulate at the luminal surface in areas where blood flow velocity and wall shear stress are low and where the permeability of the endothelial layer is enhanced. Moreover, the rate of lipid infiltration into the blood vessel walls is affected by the luminal surface concentration. These findings are consistent with chronic hypertension and elevated blood cholesterol concentrations being major risk factors for atherosclerosis.

Structure and oxygen sensitivity of nifLA promoter of Enterobacter cloacae

The nucleotide sequence of the nifLA promoter of Enterobacter cloacae E26 was determined, and the transcription start site of nifLA was mapped by the primer extension. Studies on the oxygen regulation of E. cloacae nifLA promoter with the nifL'-lacZ fusion showed that the nifLA promoter was sensitive to oxygen as Klebsiella pneumoniae nifLA promoter reported previously. Comparison between the nifLA promoter sequences of E. cloacae and K. pneumoniae revealed the presence of an 11-bp conserved sequence between the -24/-12 consensus of sigma 54-dependent promoter and NtrC binding motif. The 11-bp sequence is speculated to be involved in the oxygen regulation of the nifLA promoter of both enteric bacteria.