摘要:

Segmental aortic wall stiffness was calculated from intravascular ultrasound images and intravascular pressures in six pigs at normal and subnormal aortic pressures (21 sequences of pressures and areas before and after boli of intravenous nitroglycerin). The wall stiffness was expressed as the pressure–strain elastic modulus (Ep). TheEpwas calculated from the formula:Ep=ΔPRΔR‐1(P, pressure;R, radius) in two different ways. First from maximal and minimal values of pressure and area. Second as the slope of linear regression line of ΔPRas a function of ΔRfrom 29 simultaneous recorded pressures and images. The averageEpvalue for all sequences in the different segments was 0.58 ± 0.55 105Pa (Method 1) and 0.50 ± 0.40 105Pa (Method 2).Epincreased with the distance from the heart at normal aortic pressures. At subnormal aortic pressures after intravenous nitroglycerin this relationship was not so evident. At subnormal aortic pressures the calculatedEpvalues were significantly reduced in the lower half of the abdominal aorta. The phase lag, i. e. hysteresis, between pressure and diameter was demonstrated. Our study shows the applicability of intravascular ultrasound as a tool to evaluate arterial wall

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09226.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The established ideas of transcapillary exchange have recently been challenged based on studies in intact rats.In vivomeasurements of net fluid flux and albumin clearance in muscle (and skin) have given estimates of the reflection coefficient (s̀) for albumin of 0.98–0.99 compared to the s̀ value of 0.90 obtained by most other techniques. This discrepancy has vast consequences for the understanding of the transcapillary passage of macromolecules. A s̀ for albumin near unity implies that there is virtually no coupling between protein and fluid transfer as induced by, for example, increases in vascular hydrostatic pressures. However, there are several assumptions inherent in the seemingly straight‐forward experiments on intact rats, and in the present study we tested the hypothesis that occlusion of the femoral vein by ligation induces only moderate and transient increments of venous pressure (Pv).During control conditionsPvwas 6.3 mmHg and pressure increased to 12.8 mmHg immediately following venous occlusion. However,Pvdeclined with time and after 30 minutes of occlusion the capillary hydrostatic pressure was only increased by 3.0 mmHg. Calculations of the capillary filtration coefficient gave completely unrealistic values, close to those of maximally vasodilated skeletal muscle.The findings suggest that data obtained from intact rats, albeit important and interesting, should be evaluated with great care due to possible experimental errors in thein vivoapproaches. In particular, the technique of estimating s̀ for albumin in intact rats must be subjected to modifications before allowing any reliable conclusions. The multiple pathway model of microvascular permeability, where large pores significantly contribute to capillary wall selectivity, still seems to offer the best description of the exchange characteristics of continuous capillar

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09227.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The single injection indicator dilution technique, often used for assessing capillary permeability, was employed for estimations of the equivalent pore radius of skeletal muscle microvessels according to the theory of restricted diffusion. There are, however, certain important sources of error that must be considered in order to allow conclusions regarding the degree of restricted diffusion. In this study, we have recalculated previously published data in order to minimize the effect of heterogeneity of the second kind, i. e. a transit‐time dependence of the fractional extraction values. The method used makes it possible to calculate reliable intervals of confidence for the permeability surface area products, and hence for the permeability surface area product‐ratios (and equivalent pore radius), taking into account the maximal theoretical impact of back diffusion on measured extraction data.After correction for transit‐time dependent effects of heterogeneity, the permeability surface area product‐ratio of Cr‐EDTA to cyanocobalamine (vit. B12) from 48 measurements in eight rats was found to have a theoretical ‘upper bound’ of 2.63±0.06 and a lower bound of 2.10±0.07, corresponding to an equivalent pore radius of 60 to 109 Å. This minimum pore radius estimate was even further reduced by corrections for plasma flow dependent reductions in overall extraction fraction (heterogeneity of the first kind) to 45 Å, whereas the upper bound on pore radius was reduced to 60 Å. These data strongly support the presence of marked restricted diffusion of small solutes in the maximally vasodilated rat hindquarte

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09228.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Non‐uniformity of regional contraction may be both spatial and temporal. This study was undertaken to deal with the temporal aspects of shortening and to quantify non‐uniformity with regard to timing. Nine cats were anaesthetized and artificially ventilated. Two pairs of ultrasonic crystals were situated in the anterior midwall of the left ventricle to measure regional shortening. One pair, longitudinal segment, was oriented to align with midwall fibres. The other pair, transverse segment, was placed perpendicular to the first one. Registrations in control state, during caval occlusion, and during aortic constriction were carried out with and without isoprenaline infusion. Cyclic events were analysed in terms of phase angle, 0–2π representing one heart cycle. Transverse segments showed marked shift of duration of shortening, from 1.19π± 0.06π (meanæM) in the control state to 0.40π± 0.14π during caval occlusion with isoprenaline infusion. Duration of shortening of longitudinal segments showed less prominent shift with mean values between 1.38π and 1.11π. Regional uniformity of timing, expressed as synchronization index, varied markedly with interventions (P<0.0005). Dyssynchrony was most prominent during caval occlusion with mean values less than 0.6. A simple model of force generation for the two segments visualizes that segment shortening of the transverse segment is of shorter duration than the longitudinal segment and a common mechanism for temporal and spatial non‐uniformity within a region could be elaborated. This study quantifies both the time course of shortening and temporal non‐uniformity of two cross‐oriented segments within the s

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09229.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The impression method for assessment of subcutaneous oedema was evaluated in a rat testis model where the testicular interstitial fluid volume was changed both artificially by infusion of rat plasma and pharmacologically by administration of human chorionic gonadotrophin. Both the integral value and the impression force value, as measured with the impression method, changed with infused volume, and changes as small as 16,μl (approximately 7% of the total interstitial fluid volume in a testis) could be detected. Rats were treated with a single injection of 100 i. u. human chorionic gonadotrophin in order to induce changes in the volume of interstitial fluid in the testis. Both the integral value and the impression force value seemed to reveal information on testicular interstitial fluid volume in rats treated with human chorionic gonadotrophin that was similar to data revealed by measuring the actual fluid content in the testis. Interstitial fluid volume measured morphometrically in the contralateral testis in human chorionic gonadotrophin‐treated rats was significantly correlated to the impression force value (r= 0.75) and the integral value (r= 0.52). This rat testis model proved to be an interesting experimental set‐up for evaluation of the impression techn

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09230.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The effect of acute and sequential volaemic changes on the gastroduodenal flow of saline was assessed in 23 anaesthetized dogs following two different experimental protocols. Hypervolaemia, by i. v. infusion of saline, induced a gradual decrease on gastroduodenal flow which amounted to 76% below control values (P<0.001) when volaemic expansion attained 5% of body weight. This effect was volume dependent (17% increase on gastroduodenal flow per volume of infused saline equivalent to 0.5% of body weight,P<0.001), lasted for at least 90 minutes after infusion was completed and was also obtained by expanding previously bled animals. Hypovolaemia due to bleeding was followed by an increase on gastroduodenal flow of about 88% above control values (P<0.05) when haemorrhage was equal to 3% of body weight. This effect was also volume dependent (23 % increase on gastroduodenal flow per volume of blood shed equivalent to a 0.5% of body weight,P<0.01) and was reversed after blood volume was restored. These modifications in the resistance of the gastroduodenal segment to the flow of liquid due to acute volaemic changes suggest that the extracellular fluid volume modulates the contractile activity of the gastroduodenal portion of the gut possibly to set a gastroduodenal handling of liquid adequate to cope with volaemic imbalances.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09231.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Using a freezing point depression method osmolality in the intestinal tissue of four mammals (gerbils, guinea‐pigs, rabbits and rats) was estimatedin vivo, during fluid transport from an isotonic electrolyte‐glucose solution. Net fluid transport was also measured. In gerbils, guinea‐pigs and rabbits tissue osmolality was also estimated duringin vitroconditions. A marked hyperosmolality was observedin vivoin the upper parts of the villi of all four mammals studied. The tissue osmolality was significantly higher than that seen in the same species duringin vitroconditions. A villus hyperosmolality was observed also in species which exhibited a net fluid secretion (guinea‐pig, rabbit ileum), indicating that the fluid secretion emanated from the intestinal crypts. Based on the results of the present experiments and on observations made in earlier experiments performed on the cat, it is proposed that the villus hyperosmolality is created by a countercurrent multiplier present in the intestinal villus. The hyperosmolar compartment in the villus tissue creates the force that drives fluid from lumen to

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09232.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The aim of this study was to determine the potential value of extracellular fluid (ECF) lactate, inosine and hypoxanthine for monitoring the disturbance in energy metabolism associated with kidney ischaemia and recirculation, using intrarenal microdialysis as sampling technique. Normothermic ischaemia was produced in rats by clamping of the left renal pedicle. Microdialysis probes were implanted into the renal cortex and the medulla, respectively. Dialysates were collected in 10‐minute fractions before, during 20 (Group A) or 40 minutes (Group B) ischaemia and 2 hours of recirculation. Samples were analysed by HPLC for lactate, inosine and hypoxanthine. Ischaemia caused a dramatic increase of extracellular fluid lactate, inosine and hypoxanthine in both groups, reflecting the disturbance of energy metabolism. The basal extracellular fluid level of lactate as well as that during ischaemia was markedly higher in the medulla compared to cortex, whereas the relative change in lactate concentration was similar (i. e. about 4‐fold). In group A all three metabolites returned to the pre‐ischaemic level within 20 minutes after reperfusion. However, while inosine and hypoxanthine returned promptly to base line in Group B, recovery of lactate varied dramatically between animals suggesting a persistent metabolic disturbance in some rats.Our results indicate that extracellular fluid lactate, inosine and hypoxanthine, measured by intrarenal microdialysis, may be useful for monitoring of the energy state of the kidney during normothermic ischaemia and that extracellular fluid lactate may be a sensitive indicator of post‐ischaemic disturbances in energy met

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09233.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The present study has examined the synthesis of dopamine froml‐DOPA in kidney slices and in kidney homogenates of 3‐ and 24‐month‐old rats. The deamination of newly‐formed dopamine into 3,4‐dihydroxyphenylacetic acid (DOPAC) was also studied. The assay ofl‐DOPA, dopamine, noradrenaline and DOPAC was performed by high pressure liquid chromatography with electrochemical detection. Incubation of renal slices and homogenates of whole kidney with exogenousl‐DOPA (0.1–100μm) resulted in a concentration‐dependent formation of both dopamine and DOPAC. At 50 and 100μml‐DOPA, but not at lower concentrations (10 and 25μM), the total amounts of dopamine and DOPAC formed were significantly greater in kidney slices obtained from 3‐month‐old rats. By contrast, the total amount of dopamine and DOPAC formed was greater in homogenates of renal tissues from aged rats than from young animals; this was particularly evident at 5.0 and 10.0μml‐DOPA in the incubation medium. However, the DOPAC/dopamine ratios, both in kidney slices and kidney homogenates, were found to be higher in young rats than in old rats. The present results suggest an impairment in the formation of dopamine and of its deamination into DOPAC in renal tissues of aged rats; however, the reduced synthesis of dopamine does not appear to be the result of a decreased activity of the enzyme aro

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09234.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

We have shown previously that gastric sodium loading releases vasoactive intestinal peptide from the intestine and in rabbits on a low sodium diet it appears to decrease vasoactive intestinal peptide metabolism by the liver. To determine the contributions of the low sodium diet and the acute sodium load to changes in vasoactive intestinal peptide metabolism, metabolic clearance studies of vasoactive intestinal peptide infused intraportally were performed. These studies were performed in male New Zealand white rabbits equilibrated on normal and low sodium diets before and after an acute gastric sodium load of 1.5 mmol kg‐1. No difference was detectable in metabolic clearance rates between normal and low salt diets, however, decreases in metabolic clearance rates were observed in response to the sodium load (normal dietP<0.005, low saltP<0.0005). Secretion rates also decreased following the gastric sodium load (normalP<0.005, low saltP<0.05).We conclude that hepatic VIP metabolism is decreased by acute gastric sodium loading but it is not affected by chronic sodium intak

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1991.tb09235.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY