Neuromuscular Dysfunction Precedes Cognitive Impairment in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) develops along a continuum that spans years prior to diagnosis. Decreased muscle function and mitochondrial respiration occur years earlier in those that develop AD; however, it is unknown what causes these peripheral phenotypes in a disease of the brain. Exercise promotes muscle, mitochondria, and cognitive health and is proposed to be a potential therapeutic for AD, but no study has investigated how skeletal muscle adapts to exercise training in an AD-like context. Utilizing 5xFAD mice, an AD model that develops ad-like pathology and cognitive impairments around 6 mo of age, we examined in vivo neuromuscular function and exercise adapations (mitochondrial respiration and RNA sequencing) before the manifestation of overt cognitive impairment. We found 5xFAD mice develop neuromuscular dysfunction beginning as early as 4 mo of age, characterized by impaired nerve-stimulated muscle torque production and compound nerve action potential of the sciatic nerve. Furthermore, skeletal muscle in 5xFAD mice had altered, sex-dependent, adaptive responses (mitochondrial respiration and gene expression) to exercise training in the absence of overt cognitive impairment. Changes in peripheral systems, specifically neural communication to skeletal muscle, may be harbingers for AD and have implications for lifestyle interventions, like exercise, in AD.

Importance of microRNAs and gut microbiota in the characterization of a phenotypic drift in lupus-prone MRL/lpr mice

Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease. The cause of SLE is not only genetic; in fact, environmental factors may play a more important role in disease development. The MRL/lpr mouse model lupus-like symptoms due to multiple SLE susceptible loci in the MRL background, and offers an accelerated model compared to the MRL parent strain due to the Faslpr mutation. Recently, our laboratory witnessed a loss of disease phenotype in our in-house colony of MRL/lpr mice. We thus compared mice newly obtained from The Jackson Laboratory (JAX; Stock Number 000485) to our in-house mice. The single-nucleotide polymorphism (SNP) analysis showed no genetic drift, suggesting that environmental factors could be triggering a phenotypic drift. Surprisingly, the newly purchased JAX mice also had attenuation of glomerulonephritis. Even though JAX mice manifested similar attenuation of lupus nephritis, our in-house colony showed differences in organ weights. Furthermore, males showed a significantly higher level of anti-double stranded DNA auto-IgG consistent with germinal center maturation. In addition, in-house males had significantly higher levels of microRNA-21 and microRNA-183 explaining spleen size difference. Moreover, the composition of gut microbiota was different between in-house and new JAX mice at early age, with many groups of bacteria differing at later time points, which might explain some of the phenotypic differences. These results suggest that microRNAs and gut microbiota might be responsible for the phenotypic differences of MRL/lpr mice in JAX and our colonies as they were genetically identical. On the other hand, the attenuation of nephritis in both groups requires further investigation.

Supported by R01AR073240

Phenotypic Drift in Lupus-Prone MRL/lpr Mice: Potential Roles of MicroRNAs and Gut Microbiota

MRL/lpr mice have been extensively used as a murine model of lupus. Disease progression in MRL/lpr mice can differ among animal facilities, suggesting a role for environmental factors. We noted a phenotypic drift of our in-house colony, which was the progeny of mice obtained from The Jackson Laboratory (JAX; stocking number 000485), that involved attenuated glomerulonephritis, increased splenomegaly, and reduced lymphadenopathy. To validate our in-house mice as a model of lupus, we compared these mice with those newly obtained from JAX, which were confirmed to be genetically identical to our in-house mice. Surprisingly, the new JAX mice exhibited a similar phenotypic drift, most notably the attenuation of glomerulonephritis. Interestingly, our in-house colony differed from JAX mice in body weight and kidney size (both sexes), as well as in splenic size, germinal center formation, and level of anti-dsDNA auto-IgG in the circulation (male only). In addition, we noted differential expression of microRNA (miR)-21 and miR-183 that might explain the splenic differences in males. Furthermore, the composition of gut microbiota was different between in-house and new JAX mice at early time points, which might explain some of the renal differences (e.g., kidney size). However, we could not identify the reason for attenuated glomerulonephritis, a shared phenotypic drift between the two colonies. It is likely that this was due to certain changes of environmental factors present in both JAX and our facilities. Taken together, these results suggest a significant phenotypic drift in MRL/lpr mice in both colonies that may require strain recovery from cryopreservation.

Nox4 mediates skeletal muscle metabolic responses to exercise

OBJECTIVE

The immediate signals that couple exercise to metabolic adaptations are incompletely understood. Nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) produces reactive oxygen species (ROS) and plays a significant role in metabolic and vascular adaptation during stress conditions. Our objective was to determine the role of Nox4 in exercise-induced skeletal muscle metabolism.

METHODS

Mice were subjected to acute exercise to assess their immediate responses. mRNA and protein expression responses to Nox4 and hydrogen peroxide (H₂O₂) were measured by qPCR and immunoblotting. Functional metabolic flux was measured via ex vivo fatty acid and glucose oxidation assays using ¹⁴C-labeled palmitate and glucose, respectively. A chronic exercise regimen was also utilized and the time to exhaustion along with key markers of exercise adaptation (skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase activity) were measured. Endothelial-specific Nox4-deficient mice were then subjected to the same acute exercise regimen and their subsequent substrate oxidation was measured.

RESULTS

We identified key exercise-responsive metabolic genes that depend on H₂O₂ and Nox4 using catalase and Nox4-deficient mice. Nox4 was required for the expression of uncoupling protein 3 (Ucp3), hexokinase 2 (Hk2), and pyruvate dehydrogenase kinase 4 (Pdk4), but not the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc-1α). Global Nox4 deletion resulted in decreased UCP3 protein expression and impaired glucose and fatty acid oxidization in response to acute exercise. Furthermore, Nox4-deficient mice demonstrated impaired adaptation to chronic exercise as measured by the time to exhaustion and activity of skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase. Importantly, mice deficient in endothelial-Nox4 similarly demonstrated attenuated glucose and fatty acid oxidation following acute exercise.

CONCLUSIONS

We report that H₂O₂ and Nox4 promote immediate responses to exercise in skeletal muscle. Glucose and fatty acid oxidation were blunted in the Nox4-deficient mice post-exercise, potentially through regulation of UCP3 expression. Our data demonstrate that endothelial-Nox4 is required for glucose and fatty acid oxidation, suggesting inter-tissue cross-talk between the endothelium and skeletal muscle in response to exercise.

Variation in the coat protein sequence of British isolates of Turnip yellow mosaic virus and comparison with previously published isolates

Isolates of Turnip yellow mosaic virus (TYMV) were collected from wild cabbage (Brassica oleracea) on a 400 m stretch of Dorset coastline. The coat protein genes of four isolates showed high homology in nucleotide sequence (0.970-1.000, mean 0.987). Lower levels of homology where found to previously published sequences of Australian isolates [10] (0.725-0.775, mean 0.741). The amino acid composition of the Dorset isolates showed high levels of homology (0.964-1.000, mean 0.986). Numerous amino acid substitutions occurred between the Dorset and Australian isolates (0.705-0.819, mean 0.742). Comparison with other isolates showed large genetic distances between the Dorset isolates and both European and Australian isolates.

Goal-directed secondary motor tasks: their effects on gait in subjects with Parkinson disease

OBJECTIVE

To investigate the effects of secondary motor tasks of three levels of difficulty on the spatial and temporal parameters of gait in subjects with Parkinson disease (PD) compared with control subjects.

DESIGN

A two-group repeated measures design using a sample of convenience. Subjects performed 10-meter gait trials walking (1) freely, (2) carrying a tray, and (3) carrying a tray with four plastic glasses.

SETTING

Subjects were tested in the gait laboratory at Kingston Centre, Victoria, Australia.

SUBJECTS

Twelve subjects with PD and 12 control subjects matched for age, height, and sex were recruited from the Movement Disorders Clinic at Kingston Centre.

OUTCOME MEASURES

Gait speed, stride length, cadence, and the proportion of the walking cycle spent in double limb support were measured in moderately disabled subjects with PD and control subjects.

RESULTS

For all of the walking conditions, subjects with PD walked more slowly (F(1,22) = 16.54, p = .001, partial nu2 = .429) and with shorter steps (F(1,22) = 15.07, p = .001, partial nu2 = .406) than control subjects. In addition there were significant group by condition interaction effects for gait speed (F(2, 44) = 4.42, p = .018, partial nu2 = .167) and stride length (F(2, 44) = 4.95, p = .012, partial nu2 = .184). There was little deterioration in gait when subjects in either group carried a tray while walking compared with free walking; however, when required to carry four plastic glasses on the tray while walking, subjects in the PD group showed marked deterioration in gait speed (t(11) = 3.19, p = .009, alpha = .025) and stride length (t(11) = 3.82, p = .003, alpha = .025). Performance in the control subjects changed only marginally across the conditions.

CONCLUSION

Subjects with moderate disability in PD experience considerable difficulty when they are required to walk while attending to a complex visuomotor task involving the upper limbs.

Psychological adjustment of children awaiting limb reconstruction treatment

The psychological profiles of 53 children aged 6-17 years, with congenital and acquired limb abnormalities attending a limb reconstruction centre, were examined to determine the level of need for pretreatment psychological intervention. The profiles of two groups presenting for treatment--patients of short stature and those with other limb abnormalities--were compared with each other and with general population norms. Standardized questionnaires were administered to patients and their parents during pretreatment assessment visits to the clinic. There were few differences between the families taking part in this study and the general population norms, or between the scores of children with short stature and those with other limb abnormalities. These results may indicate that most children awaiting limb reconstructive surgery are not in need of psychological intervention other than the support routinely offered. The findings are discussed in terms of the biases which may be reflected in the referral process, possible protective effects of family environment factors and clinical support systems, and the impact of the timing of the assessments. Implications for future research are discussed.

Effect of dietary flax oil and hypobaric hypoxia on pulmonary hypertension and haematological variables in broiler chickens

1. Three experiments were conducted with broiler chickens using hypobaric chambers and control pens, feeding diets containing 25 or 50 g flax oil/kg food or control diets with equivalent amounts of animal/vegetable (A/V) blend oil for 4 weeks. The effect of these diets on haematological variables and the extent of right ventricular hypertrophy (RVH) leading to ascites was determined. 2. Overall growth rate was not consistently affected by dietary treatment, although feeding the 25 g flax oil/kg diet reduced weight gain in week 4 of one experiment. Feeding the 50 g flax oil/kg diet but not the 25 g flax oil/kg diet reduced RVH in birds exposed to hypobaric conditions compared to feeding control diets. 3. Feeding the 50 g flax oil/kg diet under hypobaric conditions reduced the haematocrit and haemoglobin content, increased the erythrocyte deformability and the proportion of unsaturated fatty acids in the erythrocyte membranes, and reduced the whole blood viscosity compared to feeding control diets. These effects were not seen when the 25 g flax oil/kg diet was fed. The ratio of n-3 to n-6 fatty acids in erythrocyte membranes was increased in the 50 g flax oil/kg treatment group compared to controls. 4. Including 50 g flax oil/kg broiler diet reduces RVH in broiler chickens. This may be attributable in part to an increase in erythrocyte deformability from an increased proportion of unsaturated fatty acids in the erythrocyte membranes.

Effect of dietary flax oil and hypobaric hypoxia on right ventricular hypertrophy and ascites in broiler chickens

1. The effect of dietary flax oil on growth rate, blood haemoglobin content, mortality and incidence of pulmonary hypertension and ascites in broilers at ambient pressure and at reduced atmospheric pressure was examined. 2. Birds were housed either in hypobaric chambers simulating 1000, 1500 or 2200 m altitude or in pens at ambient atmospheric pressure and fed on diets containing 100 g/kg added fat as either an animal/vegetable (A/V) blend or flax oil. 3. Birds raised under hypobaric conditions had a decreased growth rate and increased mortality, blood haemoglobin content, and incidence of pulmonary hypertension and ascites compared to the groups at normal atmospheric pressure. 4. Broilers fed on the diet containing flax oil showed no difference in growth rate or blood haemoglobin content compared to birds fed on the A/V fat diet raised at the same altitude. 5. Inclusion of flax oil in the diet decreased mortality and the incidence of ascites at 2200 m and pulmonary hypertension at 1500 m. 6. Flax oil may be an effective method of reducing ascites and pulmonary hypertension in broilers without affecting performance.

The pH paradox in ischemia-reperfusion injury to cardiac myocytes

During myocardial ischemia, a large reduction of tissue pH develops, and tissue pH returns to normal after reperfusion. In recent studies, we evaluated the role of pH in ischemia/reperfusion injury to cultured cardiac myocytes and perfused papillary muscles. Acidosis (pH < or = 7.0) protected profoundly against cell death during ischemia. However, the return from acidotic to normal pH after reperfusion caused myocytes to lose viability. This worsening of injury is a 'pH paradox' and was mediated by changes of intracellular pH (pH(i)), since manipulations that caused pH(i), to increase more rapidly after reperfusion accelerated cell killing, whereas manipulations that delayed the increase of pH(i) prevented loss of myocyte viability. Specifically, inhibition of the Na+/H+ exchanger with dimethylamiloride or HOE694 delayed the return of physiologic pH(i) after reperfusion and prevented reperfusion-induced cell killing to both cultured myocytes and perfused papillary muscle. Dimethylamiloride and HOE694 did not reduce intracellular free Ca2+ during reperfusion. By contrast, reperfusion with dichlorobenzamil, an inhibitor of Na+/Ca2+ exchange, decreased free Ca2+ but did not reduce cell killing. Thus, the pH paradox is not Ca(2+)-dependent. Our working hypothesis is that ischemia activates hydrolytic enzymes, such as phospholipases and proteases, whose activity is inhibited at acidotic pH. Upon reperfusion, the return to normal pH releases this inhibition and hydrolytic injury ensues. Increasing pH(i) may also induce a pH-dependent mitochondrial permeability transition and activate the myofibrillar ATPase, effects that increase ATP demand and compromise ATP supply. In conclusion, acidotic pH is generally protective in ischemia, whereas a return to physiologic pH precipitates lethal reperfusion injury to myocytes.

Inhibition of Na+/H+ exchange preserves viability, restores mechanical function, and prevents the pH paradox in reperfusion injury to rat neonatal myocytes

Rat neonatal myocytes exposed to 2.5 mM CaCN and 20 mM 2-deoxyglucose at pH 6.2 (chemical hypoxia) quickly lose viability when pH is increased to 7.4, with or without washout of inhibitors--a 'pH paradox'. In this study, we evaluated the effect of two Na+/H+ exchange inhibitors (dimethylamiloride and HOE694) and a Na+/Ca2+ exchange inhibitor (dichlorobenzamil) on pH-dependent reperfusion injury. Intracellular free Ca2+ and electrical potential were monitored by laser scanning confocal microscopy of rat neonatal cardiac myocytes grown on coverslips and co-loaded with Fluo-3 and tetramethylrhodamine methylester. After 30-60 min of chemical hypoxia at pH 6.2, mitochondria depolarized and Ca2+ began to increase uniformly throughout the cell. Free Ca2+ reached levels estimated to exceed 2 microM by 4 h. Washout of inhibitors at pH 7.4 (reperfusion), with or without dichlorobenzamil, killed most cells within 60 min, despite a marked reduction of Ca2+ in dichlorobenzamil-treated cells. Reperfusion at pH 7.4 in the presence of 75 microM dimethylamiloride or 20 microM HOE694, or at pH 6.2, prevented cell death. HOE694-treated cells placed into culture medium recovered mitochondrial membrane potential. In most cells, this occurred before normal Ca2+ was restored. Contracted myocytes re-extended over a 24-h-period. By 48 hours, most cells contracted spontaneously and showed normal Ca2+ transients. Our results indicate that Na+/H+ exchange inhibition protects against pH-dependent reperfusion injury and facilitates full recovery of cell function.

Intracellular pH and Ca2+ homeostasis in the pH paradox of reperfusion injury to neonatal rat cardiac myocytes

Ischemia is characterized by anoxia and a large decrease of tissue pH. After a critical period of ischemia, reperfusion precipitates irreversible injury. Previous work showed that reperfusion injury to cultured neonatal myocytes was precipitated by a rapid return to physiological pH, a "pH paradox" (Bond, J., B. Herman, and J. Lemasters. Biochem. Biophys. Res. Commun. 179: 798-803, 1991). The aim of this study was to measure intracellular pH (pHi) and cytosolic free Ca2+ during the pH paradox of reperfusion injury to cultured neonatal rat cardiac myocytes. pHi and free Ca2+ were measured by ratio imaging of 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein and fura 2 fluorescence. To simulate ATP depletion and acidosis of ischemia, myocytes were incubated with 20 mM 2-deoxyglucose plus 2.5 mM NaCN at pH 6.2. During simulated ischemia, pHi dropped to < 6.5 and subsequently remained constant. During this time, some blebbing but little hypercontraction occurred. After 3 or 4 h of simulated ischemia, inhibitors were removed and cells were incubated at pH 7.4 to simulate reperfusion. pHi began to increase, blebbing accelerated, and myocytes hypercontracted. As pHi increased, viability was lost. The same occurred if pH was increased but metabolic inhibitors were not removed. Monensin, a Na(+)-H+ ionophore, accelerated the increase of pH after reperfusion and hastened cell killing. Hypercontraction, blebbing, and loss of viability did not occur when inhibitors were removed at pH 6.2 or in the presence of dimethylamiloride, an inhibitor of Na(+)-H+ exchange. Protection was associated with maintenance of an acidotic pHi. Free Ca2+ progressively increased during simulated ischemia. After simulated reperfusion, free Ca2+ increased further.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel cytotoxicity screening assay using a multiwell fluorescence scanner

A new assay using a multiwell fluorescence scanner was developed for screening cytotoxicity to cells cultured in 96-well microtiter plates. The assay is based on binding of propidium iodide to nuclei of cells whose plasma membranes have become permeable due to cell death. Fluorescence of propidium iodide measured with a multiwell fluorescence scanner increased in proportion to the number of permeabilized cells. After ATP depletion of hepatocytes and neonatal cardiac myocytes with metabolic inhibitors ("chemical hypoxia"), and exposure of Madine Darby canine kidney cells to the toxic chemical, HgCl2, propidium iodide fluorescence progressively increased. Increases of fluorescence were linearly proportional with release of lactate dehydrogenase into the culture medium. Employing this cytotoxicity screening assay, protection by various agents against lethal injury was evaluated in cultured hepatocytes during chemical hypoxia. Inhibitors of cysteine proteases (i.e., antipain, leupeptin, E-64), serine proteases (i.e., PMSF), and aspartic acid proteases (i.e., pepstatin A) did not protect against chemical hypoxia. In contrast, 1,10-phenanthroline, an inhibitor of metalloprotease, markedly protected against the onset of cell death during chemical hypoxia. Half-maximal protection after 60 min occurred at 0.5 microM. Phospholipase inhibitors, chlorpromazine (50 microM) and mepacrine (50 microM), also substantially retarded cell killing. U74006F, an inhibitor of lipid peroxidation, slowed cell killing to a lesser extent during chemical hypoxia and after oxidative stress with t-butyl hydroperoxide. Calciphor, a dimer of prostaglandin B1, did not protect against cell killing during chemical hypoxia or t-butyl hydroperoxide toxicity. In conclusion, this high capacity cytotoxicity assay for cells cultured in 96-well microtiter plates is suitable for rapid screening of potential cytoprotective agents in a variety of cell types.

Protection by acidotic pH against anoxia/reoxygenation injury to rat neonatal cardiac myocytes

We assessed the effect of acidosis on cell killing during anoxia and reoxygenation in cultured rat neonatal cardiac myocytes. After 4.5 hours of anoxia and glycolytic inhibition with 2-deoxyglucose, loss of viability was greater than 90% at pH 7.4. In contrast, at pH 6.2-7.0, viability was virtually unchanged. To model changes of pH and oxygenation during ischemia and reperfusion, myocytes were made anoxic at pH 6.2 for 4 hours, followed by reoxygenation at pH 7.4. Under these conditions, reoxygenation precipitated loss of viability to about half the cells. When pH was increased to 7.4 without reoxygenation, similar lethal injury occurred. No cell killing occurred after reoxygenation at pH 6.2. We conclude that acidosis protects against lethal anoxic injury, and that a rapid return from acidotic to physiologic pH contributes significantly to reperfusion injury to cardiac myocytes - a 'pH paradox'.

Recovery of cultured rat neonatal myocytes from hypercontracture after chemical hypoxia

Cardiac myocytes exposed to anoxia hypercontract into a blebbed, rounded mass. Such hypercontraction is usually considered a manifestation of irreversible injury. Here, we studied functional recovery, long-term viability and ATP levels of cultured neonatal rat cardiac myocytes after metabolic inhibition with cyanide and 2-deoxyglucose, a model of 'chemical hypoxia' which mimics the ATP depletion and reductive stress of hypoxia. After addition of inhibitors, 5-day cultured myocytes ceased spontaneous contractions within 1-2 min, blebbed and hypercontracted after 35 min, and lost viability after 100 min as assessed by nuclear labelling with propidium iodide. 11-day cultured myocytes exhibited a similar progression of injury. When the metabolic inhibitors were removed, spontaneous contractions resumed after an average of 11 min in non-hypercontracted myocytes. In hypercontracted myocytes, weak contractions resumed after 35 min, regardless of the length of time spent in the hypercontracted state, but restoration of strong synchronous contractions took hours. Recovering cells remained viable and exhibited spontaneous contractions through 24 hours of observation, whereas contractility never returned in propidium iodide-labelled cells. ATP levels decreased rapidly after chemical hypoxia and were partially restored upon washout of inhibitors. ATP recovery was similar in non-hypercontracted and hypercontracted cells. Thus, contractile dysfunction during recovery in hypercontracted cells was not due to lack of regeneration of ATP. In conclusion, hypercontracture is not a manifestation of irreversible injury. Contractile dysfunction following recovery from hypercontracture observed here may represent 'in vitro stunning'.

Solubilization of rat liver inositol 1,4,5-trisphosphate receptor

High affinity Ins(1,4,5)P3-binding sites of permeabilized hepatocytes are probably the ligand recognition sites of the receptors that mediate the effects of Ins(1,4,5)P3 on intracellular Ca2+ mobilization. We have now solubilized these sites from rat liver membranes in the zwitterionic detergent, CHAPS, and shown that the solubilized sites bind Ins(1,4,5)P3 with an affinity (Kd = 7.26 +/- 0.52 nM, Hill coefficient h = 1.05 +/- 0.06) similar to that of the sites in native membranes (Kd = 6.02 +/- 1.57 nM, h = 0.99 +/- 0.02). ATP and a range of inositol phosphates (Ins(2,4,5)P3 Ins(4,5)P2, and inositol 1,4,5-trisphosphorothioate) also bound with similar affinities to the native and solubilized sites. Solubilization of the liver InsP3 receptor will allow its further characterization, purification, and comparison of its properties with those of InsP3 receptors already purified from cerebellum and smooth muscle.

Polymers of Cu/Zn superoxide dismutase produced by cross-linking with glutaraldehyde

Soluble polymers of bovine Cu/Zn superoxide dismutase (EC 1.15.1.1) have been prepared using the homobifunctional cross-linking reagent, glutaraldehyde. A form of the enzyme, a tetramer, with a molecular weight of 64,000 has been purified by gel filtration. The functional properties of the tetramer have been investigated. Reconstitution with copper and zinc was required for full activity. After metal reconstitution, the specific activity of the tetramer was shown to be close to 90% that of the native dimeric enzyme. The serum half-life of the tetramer in rats was found to be increased by a factor of six when compared with native superoxide dismutase. The tissue distribution of the two forms was also found to be different with the tetramer accumulating predominantly in the liver.

Effects of Na saccharin feeding and urine on barrier properties of excised rat urinary bladder

When male rats of certain strains are fed a diet with 3% or more Na saccharin, their urinary bladders develop epithelial hyperplasia and a greater incidence of tumors. Since the daily dose of saccharin is high, a link between tumor formation and the disruption of urothelial physiologic and biochemical processes has been sought. We fed male and female Sprague-Dawley rats a saccharin-free or 7.5% Na saccharin diet for 1 month. Excised bladders were mounted in flux chambers and exposed to Krebs-Ringer bicarbonate solution (KRB) or urine. Bioelectric properties and 22Na, 36Cl, and [14C]mannitol or [3H]mannitol unidirectional fluxes were measured by conventional techniques. No differences were noted between bladders from male and female animals or between Na saccharin-fed animals and animals fed the saccharin-free diet. When both surfaces of the epithelium were exposed to KRB, transepithelial dc conductance fell over 4 hr to 50% of the initial value. Conductance averaged 1.4 mS/cm2. Transepithelial potential difference (PD) was usually lumen negative and averaged 0.7 mV. Unidirectional permeability coefficients for 36Cl, 22Na, and radiomannitol were symmetric, proportional to conductance, and followed a rank order compatible with unrestricted passive diffusion. Exposure of the bladder lumen to urine from animals fed saccharin-free or Na saccharin diet hyperpolarized the transepithelial PD by more than 5 mV and raised conductance nearly threefold. Permeability coefficients remained symmetric and compatible with passive diffusion. Exposure of the lumen to solutions with the K+, Na+, and Cl concentrations and osmolality of urine simulated the conductance and PD effects of urine. We conclude that Na saccharin feeding or urine with saccharin does not uniquely affect the permeability of the excised preparation. Small hydrophilic solutes appear to cross the bladder epithelium through paracellular channels which increase in aggregate area during exposure of the lumen to urine. The hyperpolarization induced by lumenal urine is the consequence of the transepithelial K+ gradient.

The second international reference preparation of procaine benzylpenicillin in oil with aluminium monostearate

The second International Reference Preparation of Procaine Benzylpenicillin in Oil with Aluminium Monostearate was established in replacement of the first international reference preparation. The blood-level duration test (WHO Requirements for Biological Substances, No. 9), used to evaluate batches of manufactured material in relation to this reference preparation, was revised to relate to the new reference preparation. Thus a batch now passes the test if the lower confidence limit of the ratio is greater than 0.45, instead of 0.50-the value that related to the first international reference preparation. This change will ensure that material passing the test in the future will be of the same quality as in the past.

The second international reference preparation of viomycin

The first International Reference Preparation of Viomycin was replaced by the second international reference preparation, consisting of material from the batch that provided the second Working Standard of the US Food and Drug Administration. The International Unit of viomycin was redefined as the activity contained in 0.0012285 mg of the second international reference preparation. Examination of batches of viomycin sulfate from the various sources of production showed that the second international reference preparation was suitable for their assay, whereas a sample previously proposed as the international standard of viomycin was unsatisfactory.

The international standard for rolitetracycline

An International Standard for Rolitetracycline has been established and the international unit of this antibiotic defined as the activity contained in 0.001004 mg of the international standard. The definition of the international unit was based on the results of a collaborative assay in which 8 laboratories in 6 different countries participated; a total of 133 assays were performed. The assay was in terms of the Working Standard of the USA Food and Drug Administration; mean potencies for individual laboratories varied within a range of only 2% of the mean for all assays although 7 different test organisms were used in both diffusion and turbidimetric assays. Individual assays, however, provided potencies that varied within a range of 40%.

The international reference preparation of colistin methane sulfonate

The international unit of colistin methane sulfonate has been defined by collaborative assay as the activity contained in 0.00007874 mg of the international reference preparation. The definition was based on results from 7 laboratories in 5 countries which carried out assays against their existing national standards. Because of the complex heterogeneity in composition of this antibiotic the international reference preparation was not designated as an international standard.

The international standard for colistin

An International Standard for Colistin has been established and the International Unit defined as the activity contained in 0.00004878 mg of this preparation. The unit was defined on the basis of a collaborative assay in which nine laboratories from six different countries participated. The material used to prepare the international standard had been manufactured in Japan; it was shown to have a composition similar to that of material produced in Europe and to be suitable for the assay of colistin from the existing sources of manufacture.

The second international standard for chlortetracycline

As supplies of the International Standard for Chlortetracycline were practically exhausted, it was replaced. The potency of the second international standard was defined on the basis of an international collaborative assay comprising 157 individual assays performed in 9 laboratories in 6 countries. The mean potencies obtained in the participating laboratories, although they varied by only 7%, were heterogeneous. However, the mean potency for all the laboratories combined did not differ significantly from that of the first international standard. The International Unit for chlortetracycline was therefore defined as the activity contained in 0.001 mg of the second international standard, corresponding to a potency of 1 000 IU/mg.

Induced corneal opacities in the rat

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The international reference preparation of gramicidin

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to establish an International Reference Preparation of Gramicidin. This preparation was needed to standardize preparations of gramicidin containing predominantly gramicidin A, B and C, for which purpose the International Reference Preparation of Gramicidin S cannot be used. A batch of 100 g of crystalline gramicidin obtained in 1963 was distributed into ampoules in 55 mg amounts and dried in vacuo; the ampoules were then filled with dried nitrogen and sealed. The proposed international reference preparation was assayed biologically against the Master Standard of Gramicidin of the US Food and Drug Administration in 7 laboratories in 6 countries by turbidimetric methods.Significant curvature of the dose-response lines was found for most assays; no single transformation improved the linearity of assays from all laboratories. Although significant heterogeneity of potencies was obtained in 5 laboratories the mean potency ratios for all laboratories only varied over a range of 5% to 6%. The composition of the material is 7% gramicidin B, 50% gramicidin A and 25% gramicidin C; preparations of gramicidin containing appreciably higher concentrations of gramicidin B can be expected to give invalid assays against the international reference preparation.The material has been established as the International Reference Preparation of Gramicidin with a defined potency of 1000 IU/mg. The International Unit of Gramicidin is defined as the activity of 0.001 mg of the International Reference Preparation of Gramicidin.

The second International Standard for Oxytetracycline

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to establish a second International Standard for Oxytetracycline, since stocks of the first International Standard were depleted. A batch of 500 g of oxytetracycline dihydrate obtained in 1963 was distributed into ampoules in 125-mg amounts; the ampoules were filled with dried nitrogen and sealed. The usual procedure of exhaustively drying the material was omitted since removal of water of hydration adversely affects stability of oxytetracycline dihydrate. The proposed replacement material has been assayed biologically in terms of the first International Standard in 9 laboratories in 7 countries by means of plate-diffusion and turbidimetric assays.Significant heterogeneity of the potencies obtained by the different laboratories and within 3 laboratories was not attributable to any known differences in assay technique; the weighted mean potencies obtained by all laboratories were within a range of +/-2% of the over-all mean potency.The potency of the second International Standard is approximately 3% less than that of the first International Standard but no significant difference in composition or purity could be detected by a variety of chemical and physical analytical methods. The material has been established as the second International Standard for Oxytetracycline with a defined potency of 880 IU/mg. The International Unit of Oxytetracycline is defined as the activity of 0.0011364 mg of the second International Standard of Oxytetracycline.

Evaluation of the blood level duration properties of procaine benzylpenicillin in oil with aluminium monostearate (PAM)

The study of procaine benzylpenicillin in oil with aluminium monostearate (PAM) described in this paper was undertaken to devise laboratory assay methods, based on animal tests, to evaluate those properties of PAM responsible for the persistence of penicillin in the circulation, as a preferable substitute for the existing test in man. Comparative studies of a number of batches of PAM in man proved, with statistical certainty, that the duration of the blood level of penicillin which they produced varied from batch to batch. The chemical and physical properties of the batches gave inadequate characterization and were of no value in assessing material for clinical use. A blood level duration test in rabbits was developed which reflected the blood level duration properties shown in man. The test was incorporated in the Requirements for Procaine Benzylpenicillin in Oil with Aluminium Monostearate that were set up by the WHO Expert Committee on Biological Standardization to ensure the suitability of batches for clinical use. An International Reference Preparation was necessary and was established. Batches of PAM in use in the field by WHO in anti-yaws campaigns were examined by the test described and found to be satisfactory.