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At least 325 records · Page 18Linked to original sources
PubMed1998

Determination of diethylpyrocarbonate-modified amino acid residues in alpha 1-acid glycoprotein by high-performance liquid chromatography electrospray ionization-mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry.

The chemical modification reagent diethylpyrocarbonate (DEPC) was used to modify alpha 1-acid glycoprotein (orosomucoid, OMD) under various conditions. The extents of DEPC modification of the histidine and tyrosine residues were followed by UV spectrophotometry. The resulting modified OMD was analyzed using enzyme digestion, reverse-phase HPLC, electrospray ionization-mass spectrometry (ESI/MS), and matrix-assisted laser desorption ionization time-of-flight-mass spectrometry (MALDI-TOF/MS). The inherent problem of instability of DEPC-modified histidine residues was overcome by adjusting the time scale of the postreaction processing of modified OMD. There were observed differences in reactivity of histidine 97 and histidine 100 that were consistent throughout the pH range 6-8. Furthermore, several lysine residues were modified and the amount of modification increased over the pH range 6-8. These experiments show that HPLC-ESI/MS and MALDI-TOF/MS analysis coupled with enzyme digestion provide the necessary information to describe the reaction of DEPC with OMD. In addition, the results provide the carbethoxy-histidine stability and histidine reactivity information of DEPC-modified OMD necessary for the design of experiments to characterize the drug binding properties of OMD.

Amino Acid Sequence↗
PubMed1995

Malondialdehyde-modified HDL leads to accumulation of cholesterol in rat liver endothelial cells.

In order to study in vivo the effect of modified high density lipoprotein (HDL) on the movement of free cholesterol to liver cells and bile, we injected i.v. into rats, native or malondialdehyde modified HDL labelled with [14C]cholesterol. Bile analysis indicated that the contribution of labelled cholesterol to bile acid secretion was diminished in the group receiving MDA-modified HDL when compared to control group. On the other hand, the liver analysis revealed higher radioactivity in the treated group. A separation of liver cells into parenchymal, endothelial, and kupffer at 90 min after the injection of MDA-modified HDL or native HDL indicated that the endothelial cell uptake of labelled free cholesterol from MDA-modified HDL was 2.6-fold higher than for native HDL. It is suggested that liver endothelial cells may be involved in the protection against atherogenoic oxidized lipoprotein. However, with regard to our finding, the uptake of cholesterol from modified HDL was detrimental to bile acid secretion.

Animals↗
PubMed2000

Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay.

Batch sorption experiments performed on Cr(VI) species sorption showed a significantly enhanced removal of inorganic hexavalent chromium anionic species from aqueous solution by montmorillonite clays modified with quaternary amine, hexadecyltrimethylammonium (HDTMA) bromide. Unmodified clay had no affinity for chromium(VI) species. The sorption of Cr(VI) species has been carried out as a function of pH, contact time, adsorbate concentration (4.14x10(-5) to 8.62x10(-3) M), and temperature (5-45 degrees C). The surfactant-modified clay surface was stable when exposed to extremes in pH. The optimum pH for maximum sorption of Cr(VI) species was found to be at pH 1 and was constant between pH 2 and pH 6. The sorption data obtained was well described by DKR and Langmuir sorption isotherms. Sorption energy (E) for (i) surfactant sorption by montmorillonite clay and (ii) sorption of chromium(VI) species by surfactant modified clay have been computed from the DKR equation. Sorption energy evaluated for the sorption of both surfactant and Cr(VI) species showed that an ion-exchange mechanism was operative. The mechanism of retention appears to be replacement of counterion of the surfactant by Cr(VI) anionic species. Adsorbent capacity for the sorption of Cr(VI) species has been evaluated from the Langmuir sorption isotherm data. Thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees ) for surfactant sorption on montmorillonite clay and Cr(VI) sorption by modified clay have been evaluated. The specific rate constant for sorption of Cr(VI) species on modified montmorillonite was rapid during the first 10 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) species onto modified montmorillonite clay followed first-order rate kinetics. Copyright 2000 Academic Press.

Journal Article↗
PubMed1982

Modified axonemes and ciliary membranes in three polychaete species.

In living Ophryotrocha puerilis, Polyophthalmus pictus and Dinophilus gyrociliatus no modified cilia are present. Treatment with hyper- and hypotonic magnesium chloride solutions leads to the formation of either cilia with dilated tips or discocilia (paddle cilia). Discocilia show axoneme loops within distal swellings of the ciliary membranes. Both types of modified cilia regain their normal appearance if they are allowed to recover in seawater. The total number of discocilia and the diameter of the loops are inversely related to the osmolarity of the magnesium chloride solution used. Even isotonic solutions of magnesium chloride, which are usually used to anaesthetize marine worms, readily induce modified cilia. This indicates that the effect is not merely due to osmotic conditions. Glutaraldehyde and osmium tetroxide may act in the same way to induce modified cilia, a fact which may account for the numerous TEM and SEM documentations of modified cilia in various marine invertebrates. Which cilia in a particular species are modified varies from one specimen to another.

Animals↗
PubMed1991

Interaction of 4-aminopyridine with normal and chloramine-T-modified K channels of neuroblastoma cells.

The steady-state effects and rate of action of 4-aminopyridine (4-AP) on normal and chloramine-T (CL-T)-modified voltage-dependent potassium (K) currents were studied in neuroblastoma cells with the whole-cell voltage-clamp current recording technique. 4-AP apparently slows both the activation and inactivation of the normal current but does not modify the time course of the CL-T-modified current. These differential effects of 4-AP are interpreted as resulting from the existence of two types of K channels with different 4-AP sensitivities under normal conditions and similar 4-AP sensitivities after CL-T, which furthermore slows their inactivation [8, 9]. While the onset of 4-AP action on the normal current is delayed and can be described by the difference of two exponentials, the onset of 4-AP action on CL-T-modified current starts immediately after the external application of the drug and can be described by the sum of two exponentials. The 4-AP-induced block of the normal current exhibits use-dependent features and is relieved by long conditioning depolarizations. In contrast, the block of the CL-T-modified current is not use-dependent. At high 4-AP concentrations (1-10 mM), the steady-state block of the normal current reaches a saturating value of 95%, while the steady-state block of the CL-T-modified current and the "unblocked" normal current only reaches a saturating value of 35%. The results suggest that CL-T inhibits a channel or membrane constituent which contributes to the inactivation of channels and increases their apparent affinity for 4-AP when they are in closed or open states.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗
PubMed1983

Identification of a locus modifying the electrophoretic mobility of malate dehydrogenase isozymes in incense-cedar (Calocedrus decurrens), and its implications for population studies.

Using megagametophyte (maternal haploid) and embryo (diploid) tissues of incense-cedar seeds, the expression of one of three malate dehydrogenase (MDH) loci was found to be influenced by a second, unlinked, modifier locus. Whereas alleles of the affected structural locus are codominant, the modifier alleles show dominance. The action of the modifier, limited to 1 of 28 structural loci examined, results in a shift of electrophoretic mobility detectable in conventional starch gels. Both the structural and the modifier MDH loci are polymorphic in all populations surveyed. Studies of genetic variation in natural populations made without rigorous genetic analysis may not detect such modification. By misinterpreting the genetic basis of enzyme phenotypes, such undetected modification can result in overestimates of genetic diversity in natural populations and can cause an apparent excess of homozygotes relative to expectations. These effects on allele and genotype frequency estimates are dependent on the levels of polymorphism at both the structural and the modifier loci. Using procedures common to many surveys of electrophoretic variation, the frequency of a recessive modifier allele could be as high as 0.3 before being detected.

Electrophoresis↗
PubMed1988

Differential effect of food on kinetics of bromocriptine in a modified release capsule and a conventional formulation.

The influence of food on release of drug from a modified release capsule of bromocriptine 5 mg (Parlodel SRO) and a conventional formulation of bromocriptine 5 mg has been studied in 8 healthy male volunteers. Both formulations produced objective and subjective effects, such as orthostatic reactions, nausea, dizziness, vomiting and nasal congestion. The modified release capsule caused fewer side-effects than the normal capsule. Both formulations had less cardiovascular effect in the fed than in the fasting state. There was no significant difference between the normal and the modified release capsules taken fasting or after a meal in terms of the AUC extrapolated to infinity. The relative bioavailability of the 5 mg modified release capsule was 84.6% of the normal capsule under fasting conditions and 107.5% after food. In contrast to the virtually unchanged extent of absorption, the rate of absorption was markedly affected by food, especially from the conventional capsule. The mean time of 50% absorption increased from 1.06 h (fasting) to 3.2 h (fed), whereas for the modified release capsule food mainly resulted in an increased lag time of absorption. The almost instantaneous dissolution of bromocriptine from the normal capsule in vitro (both in HCl and fasting human gastric juice) and the delay of absorption after a meal in vivo suggest that the rate limiting step in absorption of the normal capsules is delivery of released drug from the stomach to the small intestine, which is delayed by food. Both the modified release 5-mg capsule and the normal 5-mg capsule showed extended suppression of prolactin over 36 h, in all subjects, both fasted and after a meal.

Adult↗
PubMed1988

Pharmacokinetics of low-dose oral modified release, soluble and intravenous aspirin in man, and effects on platelet function.

The pharmacokinetics of low-dose aspirin and the resulting salicylic acid were studied in 6 healthy volunteers. Each received a single 50-mg dose of (1) oral modified release capsules, (2) oral solution and (3) intravenous solution. The volunteers also received 50 mg modified release capsules daily for 6 days to determine the effect on collagen, ADP and arachidonate induced platelet aggregation and thromboxane production, and to compare the pharmacokinetics after repeated dosing with the parameters obtained after the single dose. The formulation and route of administration profoundly influenced several pharmacokinetic parameters for aspirin: the maximum concentration (Cmax, ng.ml-1) was 221 and 191 after modified release for single and chronic dosing respectively, 1323 after the oral solution and 6000 after intravenous injection; the time to achieve this maximum concentration (tmax, h) was 3.42 and 3.02 after modified release for single and chronic dosing respectively, and 0.29 after the oral solution; the area under the plasma drug concentration versus time curve (AUC, microgram.h.ml-1) was 0.38 and 0.27 after modified release single and chronic dosing respectively, 0.68 after the oral solution and 1.57 after intravenous injection. The elimination of aspirin after the two solutions was at least biphasic. The terminal phase rate constant ranged from 1.52 h-1 after intravenous injection to 1.88 h-1 after the oral modified release form. The absorption of the oral forms of aspirin was complete as reflected by the total recovery of the doses as salicylic acid in urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1981

Effect of chemical modifiers of amino acid residues on proton conduction by the H+-ATPase of mitochondria.

The effect of chemical modifiers of amino acid residues on the proton conductivity of H+-ATPase in "inside out" submitochondrial particles has been studied. Treatment of submitochondrial particles prepared in the presence of EDTA (ESMP) with the arginine modifiers, phenylglyoxal or butanedione, or the tyrosine modifier, tetranitromethane, caused inhibition of the ATPase activity. Phenylglyoxal and tetranitromethane also caused inhibition of the anaerobic release of respiratory delta micro H+ in ESMP as well as in particles deprived of F1 (USMP). Butanedione treatment caused, on the contrary, acceleration of anaerobic proton release in both particles. The inhibition of proton release caused by phenylglyoxal and tetranitromethane exhibition in USMP a sigmoidal titration curve. The same inhibitory pattern was observed with oligomycin and with N,N'-dicyclohexylcarbodiimide. In ESMP, relaxation of delta micro H+ exhibited two first-order phases, both an expression of the H+ conductivity of the ATPase complex. The rapid phase results from transient enhancement of H+ conduction caused by respiratory delta micro H+ itself. Oligomycin, N,N'-dicyclohexylcarbodiimide, and tetranitromethane inhibited both phases of H+ release, and butanedione accelerated both. Phenylglyoxal inhibited principally the slow phase of H+ conduction. In USMP, H+ release followed simple first-order kinetics. Oligomycin depressed H+ release, enhanced respiratory delta micro H+, and restored the biphasicity of H+ release. Phenylglyoxal and tetranitromethane inhibited H+ release in USMP without modifying its first-order kinetics. Butanedione treatment caused biphasicity of H+ release from USMP, introducing a very rapid phase of H+ release. Addition of soluble F1 to USMP also restored biphasicity of H+ release. A mechanism of proton conduction by Fo is discussed based on involvement of tyrosine or other hydroxyl residues, in series with the DCCD-reactive acid residue. There are apparently two functionally different species of arginine or other basic residues: those modified by phenylglyoxal, which facilitate H+ conduction, and those modified by butanedione, which retard H+ diffusion.

Adenosine Triphosphatases↗
PubMed2000

Modifier effects on supercritical CO2 extraction efficiency of cephalotaxine from Cephalotaxus wilsoniana leaves.

The effects of modifiers such as methanol, water, diethylamine in methanol (10 v/v %), and diethylamine in water (10 v/v %) were investigated at three different concentrations (1, 5, and 10 v/v %) of the modifiers in supercritical CO2 (SC-CO2) in order to enhance the supercritical fluid extraction (SFE) efficiency of cephalotaxine from Cephalotaxus wilsoniana leaves. Among the modifiers employed, methanol basified with diethylamine was found to greatly enhance the extraction efficiency relative to any other modifiers employed. The results suggest that cephalotaxine in plant matrices may be readily changed from SC-CO2-insoluble salt to SC-CO2-soluble free base by basified modifiers. In addition, SC-CO2 modified with basified methanol could enhance the extraction efficiency of cephalotaxine more than 30% when compared to the conventional organic solvent extraction.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Soil-modified carbon paste electrode: a useful tool in environmental assessment of heavy metal ion binding interactions.

Carbon paste electrodes (CPEs) modified with different soils in their native form were prepared to create a soil-like solid phase suitable for application in studies of heavy metal ion uptake and binding interactions. The preparation of CPEs modified with five different soils was examined and their heavy metal ion uptake behavior investigated using a model Cu(II) aqueous solution. Metal ions were accumulated under open circuit conditions and were determined after a medium exchange using differential pulse anodic stripping voltammetry, applying preelectrolysis at -0.7 V. The soil-modified CPE accumulation behavior, including the linearity of the current response versus Cu(II) concentration, the influence of the pH on the solution, and the uptake kinetics, was thoroughly investigated. The correlation between the soil-modified CPE uptake capability and the standard soil parameters, such as ion exchange capacity, soil pH, organic matter and clay content, were evaluated for all five examined soils. The influence of selected endogenous cations (K(I), Ca(II), Fe(III)) on the transfer of Cu(II) ions from a solution to the simulated soil solid phase was examined and is discussed. Preliminary examinations of the soil-modified CPE uptake behavior with some exogenous heavy metal ions of strong environmental interest (Pb(II), Hg(II), Cd(II) and Ag(I)) are also presented. This work demonstrates some attractive possibilities for the application of a soil-modified CPE in studying soil-heavy metal ion binding interactions, with a further potential use as a new environmental sensor appropriate for fist on-site testing of polluted soils.

Journal Article↗
PubMed1993

Ultrafiltration and modified ultrafiltration in pediatric open heart operations.

The capillary leak associated with cardiopulmonary bypass results in an increase in content of water in the tissues measurable by an increase in total body water after cardiac operation. Following work by Magilligan in the 1970s, ultrafiltration was introduced during bypass as a means of hemoconcentrating patients and potentially removing water from the tissues. Conventional methods proved inconsistent; thus, we modified the technique to ultrafilter the patients immediately after cessation of bypass. Modified ultrafiltration takes 10 minutes and results in an elevation of the on-bypass hematocrit to about 35% or 40%. In pilot studies comparing bypass in absence of ultrafiltration with conventional ultrafiltration and modified ultrafiltration, only the modified technique was seen reliably to reduce the elevation in total body water to only 4%, within a narrow range. Subsequent prospective studies confirmed the reduction in accumulation of total body water and also demonstrated a reduction in blood loss and in requirements for blood transfusion. Systolic blood pressure was observed to increase uniformly in all patients undergoing modified ultrafiltration. This effect was investigated and found to be associated with a marked increase in cardiac index, no change in systemic vascular resistance, a decrease in heart rate, and a marked decrease in pulmonary vascular resistance. Recently, we have demonstrated an increase in contractility and a decrease in myocardial wall volume. The modified technique of ultrafiltration has been employed successfully in more than 400 patients in our institution, and represents an excellent option for perioperative management of both accumulation of fluid in the tissues and hemodynamics after hypothermic bypass.

Adolescent↗
PubMed1996

Effective 30-hour preservation of canine lungs with modified ET-Kyoto solution.

BACKGROUND: With the aim of developing a preservation solution that can preserve donor lungs reliably for a long time, we prepared a modified ET-Kyoto solution by adding N-acetylcysteine, nitroglycerin, and dibutyryl adenosine 3', 5'-cyclic phosphate to the previously reported ET-Kyoto solution, which contains trehalose, gluconate, and hydroxyethyl starch. In this study, we examined the efficacy of modified ET-Kyoto solution in 30-hour lung preservation. METHODS: Twenty five pairs of adult mongrel dogs were divided into four groups. Donor lungs were flushed with modified ET-Kyoto solution (n = 9), with ET-Kyoto solution (n = 6), with University of Wisconsin solution group (n = 6), or with ET-Kyoto solution plus the solvents of nitroglycerin (ethanol and propylene glycol) (n = 4), then stored at 4 degrees C for 30 hours. All animals were treated with prostaglandin E1. Left lungs were transplanted and reperfused for 6 hours. RESULTS: With respect to arterial oxygen tension, peak inspiratory pressure, and wet-to-dry lung weight ratio, modified ET-Kyoto solution was significantly superior to ET-Kyoto solution. The modified ET-Kyoto solution was significantly superior to University of Wisconsin solution with respect to survival rate, arterial oxygen tension, and wet-to-dry lung weight ratio. Ultrastructural findings supported these results. CONCLUSIONS: These results suggest that modified ET-Kyoto solution is superior to University of Wisconsin solution for 30-hour lung preservation.

Acetylcysteine↗
PubMed1980

The sulphatase of ox liver. XXIII. The nature of substrate-modified sulphatase A.

An improved method is described for the preparation of milligram quantities of substrate-modified sulphatase A. The latter has the same molecular weight and the same ability to form a tetramer as has native sulphatase A. It has been shown that the modified enzyme prepared with nitrocatechol [35S]sulphate as substrate contains 1 mol 35SO24- per mol enzyme and that any treatment which causes reversion of the modified enzyme to native enzyme is accompanied by the loss of the bound SO24-. Dialysis of the 35S-modified enzyme against a solution containing SO24- causes a loss of 35SO24- with no change in the amount of modified enzyme in the preparation. It has been shown that the activation of the substrate-modified enzyme by SO24- does not lead to the formation of a third stable form of sulphatase A.

Animals↗
PubMed1977

Preparation and enzymatic hydrolysis of dinucleoside monophosphates and DNA modified with aromatic residues.

The following procedures have been used to prepare fifteen modified dinucleoside monophosphates: (a) bisulfite-catalyzed transamination with aniline to give an N4-phenylcytidine (CPh), (b) bisulfite-catalyzed transamination with beta-naphthylamine to give an N4-beta-naphthylcytidine (CbetaN), (c) alkylation with 7-bromomethylbenz[a] anthracene to afford a 7(benz[a]anthryl-7-methyl)guanosine (GMBA), and (d) reaction with N-acetoxy-2-acetylaminofluorene to give an 8-(N-2-fluorenylacetamido)guanosine (GAAF). The compounds prepared were A-CPh, CPh-A, CPh-G, U-CPh, CPh-U, A-CbetaN, CbetaN-A, G-CbetaN, CbetaN-G, U-CbetaN, CbetaN-U, GMBA-U, U-GMBA, GAAF-U, and U-GAAF. All of the modified compounds were hydrolyzed to the expected monomers with venom and spleen exonucleases. Hydrolysis by micrococcal nuclease was inhibited in the following cases: A-CPh, A-CbetaN, U-GMBA, and U-GAAF. The first three reactions above were applied to denatured calf thymus DNA to prepare modified DNA samples containing from 0.3 to 2.0% bound aromatic residues. The modified nucleic acids were completely hydrolyzed to nucleosides by the combination of venom exonuclease, deoxyribonuclease I and alkaline phosphatase. The same results were obtained with a combination of spleen exonuclease, deoxyribonuclease II, and alkaline phosphatase. Hydrolysis of the modified nucleic acids by micrococcal nuclease and alkaline phosphatase afforded primarily nucleosides, with some dinucleoside monophosphates. The amount of the latter did not exceed that found in the hydrolysis of control DNA, however. Other workers have observed inhibition of enzymatic hydrolysis of nucleic acids modified by aromatic carcinogens. We postulated that their results may have been caused by cross-links, which were avoided in our studies.

Animals↗
PubMed1991

Survival and differentiation within the adult mouse striatum of grafted rat pheochromocytoma cells (PC12) genetically modified to express recombinant beta-NGF.

Rat pheochromocytoma PC12 cells were genetically modified in vitro to express recombinant beta-nerve growth factor (beta-NGF) using a replication-deficient retroviral vector carrying the mouse beta-NGF gene and subsequently implanted into the striatum of a mouse model of Parkinson's disease. The fate of the genetically modified PC12 cells (PC12N.8) was assessed at varying times postimplantation by studying immunoreactivity (IR) to tyrosine hydroxylase (TH) or the rat NGF receptor (NGFR). In vitro, the genetically modified PC12 cells displayed a neuronal morphology in the absence of exogenous NGF which was characterized by extensive neurite outgrowth. In addition, the genetically modified PC12 displayed a catecholaminergic phenotype in vitro as assessed by TH-IR. Following implantation into the striatum, the survival of PC12N.8 cells was limited. Surviving cells could be identified by NGFR-IR, but not by TH-IR. In addition, PC12N.8 cells with a neuronal morphology similar to that observed in vitro were only rarely observed in vivo. No tumors were observed in PC12N.8 graft recipients up to 30 days postimplantation. In contrast, intrastriatal tumors were observed in 50% of the PC12 cell recipients. These data demonstrate that PC12 cells genetically modified in vitro to synthesize beta-NGF do not revert to the mitotic phenotype of the parent PC12 cell line following implantation into the adult striatum, an observation that suggests that these cells may continue to express recombinant beta-NGF in vivo. The data further suggest that the genetically modified PC12 cells lose the catecholaminergic phenotype following implantation into the striatal parenchyma.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Gland Neoplasms↗
PubMed1988

Quantification of plasma lipids and apolipoproteins in British Halflop rabbits. A comparison between normocholesterolemic rabbits, hypercholesterolemic rabbits (modified WHHL rabbits) and rabbits fed an atherogenic diet.

We have established isolation methods and developed electroimmunoassays for rabbit apolipoprotein A-I (apo A-I), apo B, apo C-III and apo E. The assays were used to characterize a hyperlipidemic strain of the British Halflop rabbits (BHL rabbits), obtained after cross-breeding with WHHL rabbits and referred to as modified WHHL rabbits, and to investigate the changes in the apolipoprotein levels induced by feeding normal BHL rabbits an atherogenic diet (0.25% cholesterol and 3% coconut oil). The modified WHHL rabbits were characterized by increased levels of apo B, apo C-III and apo E as well as cholesterol, phospholipids and triacylglycerol as compared to chow-fed BHL rabbits, while the apo A-I levels were only half of those found in the chow-fed animals. The modified WHHL rabbits had virtually no low density lipoprotein (LDL) receptor activity and a low fractional catabolic rate (FCR) of LDL. These results indicate that the modified WHHL rabbit has the homozygous form of the LDL receptor deficiency. The BHL rabbits fed the atherogenic diet showed increased levels of cholesterol, triacylglycerol, apo B, apo C-III and apo E, as compared to those of the chow-fed BHL rabbits. The apo E and apo C-III reached levels in the range of or even higher than those of the modified WHHL rabbits. The apo A-I levels on the other hand did not differ from those of the chow-fed rabbits. Feeding an atherogenic diet led to a decrease in the FCR of LDL to a level similar to that found in the modified WHHL rabbits.

Animals↗
PubMed1986

The standardisation of gauge length: its influence on the relative extensibility of natural and chemically modified pericardium.

Cyclic uniaxial load tests were performed on natural and chemically modified bovine pericardium which is used in the construction of heart valve substitutes. A template was employed to select specimens from the same sites in different pericardial sacs. When the pericardium was chemically modified by glutaraldehyde fixation as an entire sac the tissue showed increased extensibility after modification compared with the natural tissue. The undeformed stress-free length (gauge length) in both the natural and modified tissue was determined by a highly reproducible experimental method giving a coefficient of variation of less than 0.5%. Specimens excised from a natural pericardial sac demonstrated a significant increase (p less than 0.03) in length, 4.97 +/- 3.49%, after a single load cycle, compared with controls placed in isotonic saline but not mechanically tested. The test pieces had returned to their original length by 8.5 h after the mechanical test. After fixation the same specimens decreased significantly in length (p less than 0.001) by 11.18 +/- 4.28%. This shrinkage was not significantly different to that of the control specimens (11.09 +/- 2.47%) which had not been tested. Uniaxial loading of these chemically modified strips demonstrated a similar increase in tissue extensibility compared to the natural tissue if the undeformed length of the test specimen after shrinkage was used as the gauge length. After mechanical conditioning the chemically modified tissue also demonstrated a significant increase (p less than 0.001) in stress-free length (5.35 +/- 0.59% after 36 cycles, 8.92 +/- 1.50% after 2085 cycles). These deformations were not permanent. The tissue had returned to its original length after 38 h in its normal buffered glutaraldehyde storage medium. On the basis of these observations, recommendations for the clarification and standardisation of gauge length definitions were made in natural, chemically modified and mechanically conditioned tissue.

Animals↗