Relationship between minimum inhibitory concentration and stationary concentration revisited: growth rates and minimum bactericidal concentrations.
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Anti-Bacterial Agents↗
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Selecting therapeutic concentrations: minimum inhibitory concentrations vs subminimum or supraminimum inhibitory concentrations.
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Animals↗
[The influence of aging on the renin angiotensin-aldosterone system: simultaneous measurement of plasma renin substrate concentration, plasma renin activity, plasma aldosterone concentration, and plasma active and inactive renin concentrations].
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Adolescent↗
[Sodium and potassium concentration in the erythrocytes of patients undergoing chronic hemodialysis. (II).--Effects of extracellular fluid sodium concentration on the erythrocytes sodium and potassium concentration (author's transl)].
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Adult↗
High concentrations of fibronectin fragments cause short-term catabolic effects in cartilage tissue while lower concentrations cause continuous anabolic effects.
We reported earlier that Fn fragments (Fn-f) added to bovine articular cartilage cultured in serum-free DMEM cause marked elevated release of protease activity within a few days. This results in greatly elevated rates of release of proteoglycan (PG). We have now extended our studies to 4-week cultures of cartilage in the presence of 10% serum. We report here that cartilage cultured with 0.01, 0.1, and 1 microM of an amino terminal 29-kDa Fn-f in 10% serum accelerated the loss of PG from the tissue during the first few days in a concentration-dependent manner. However, beyond this period PG content decreased much more slowly. During this early period, the 29-kDa Fn-f decreased rates of protein and PG synthesis up to 50% in a concentration-dependent fashion. Beyond this period, the synthesis rates began to increase in a mode inversely related to 29-kDa Fn-f concentration, up to 135% of Fn-f free control values. However, during the entire culture period, cartilage cultured with 1 nM 29-kDa Fn-f had higher PG contents and had enhanced rates of protein and PG synthesis. Since 1 nM 29-kDa Fn-f stabilized cartilage against decreases in PG content, we tested its ability to block the activity of higher 29-kDa Fn-f concentrations. Cartilage was preincubated for 7 days with 1 nM 29-kDa Fn-f, and then the culture adjusted to 100 nM 29-kDa Fn-f to cause PG depletion. The preincubated cartilage showed markedly enhanced resistance to PG depletion. Since the protective effect was similar to known properties of IGF-1, the ability of 20 ng/ml IGF-1 to block against the effects of 100 nM Fn-f was tested and shown to be similar in magnitude to that of 1 nM 29-kDa Fn-f. We propose that the initial catabolic effects of higher concentrations of Fn-f, followed by the later anabolic effects, may aid in tissue repair. Also, the continuous anabolic effects of lower concentrations may be involved in tissue homeostasis.
Amino Acid Sequence↗
Do concentrations of neurotransmitters measured in lumbar cerebrospinal fluid reflect the concentrations at brain level?
CSF concentrations of vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), noradrenaline (NA) and dopamine (DA) were measured in the lateral ventricles and at the lumbar level in patients with normal pressure hydrocephalus (NPH). The concentrations of VIP (n = 15), NA (n = 10) and DA (n = 10) were significantly higher at the lumbar level than at the ventricular level, whereas the concentrations of CCK (n = 9) were similar at the two sites. A significant positive correlation between the concentrations measured at the two levels was found for VIP (rs = 0.65; p less than or equal to 0.01) and DA (rs = 0.94; p less than or equal to 0.001). The results indicate that the concentrations of transmitter substances measured in CSF at the lumbar level not necessarily are indicative for concentrations measured more centrally. The negative correlations between Evans ratio and L-CSF VIP (rs = -0.76; p less than or equal to 0.001), and between resistance to outflow and V-CSF as well as L-CSF CCK (rs = -0.75); p less than or equal to 0.05) might be explained by a reduction in number of cortical neurons or by disturbances in CSF dynamics in patients with NPH.
Cerebral Ventricles↗
Temporal and local concentration changes in diffusion layers at cellulose membranes due to concentration differences between the solutions on both sides of the membrane.
By means of a laser-interferometrical method diffusion layers at the interface of a noncharged cellulose membrane are studied. These layers are induced by a concentration difference between the NaCl solutions separated by the membrane. The temporal and local shift of the NaCl concentration in the diffusion layers were measured. A steady-state concentration profile could be obtained for times of 121 sec less than or equal to to less than or equal to 484 sec. The concentration profiles at any time (to less than or equal to 900) are not a linear function of the membrane surface, but could be fitted to a quadratic function. The thickness of the diffusion layers is also a function of time and its stationary value in this system is (575 +/- 49) X 10(-6)m. The role of concentration polarization for the determination of phenomenological thermodynamic coefficients of membranes is discussed and a new method is suggested, which excludes the difficulties of the concentration polarization in the diffusion layers at the membrane.
Cellulose↗
Female sex steroid concentrations in the ampullary and isthmic regions of the human fallopian tube and their relationship to plasma concentrations during the menstrual cycle.
The concentrations of estradiol-17 beta (E2) and progesterone (P) were measured in the ampullary and isthmic portions of the fallopian tube of nonpregnant menstruating women and the cyclic fluctuations were related to the concentrations of these hormones in plasma. The steroid concentrations were determined by radioimmunoassays. There was no significant difference in the isthmic and ampullary concentrations of either steroid in any of the menstrual phases. The mean value for E2 was highest in the ovulatory phase and for P during the luteal phase. The tissue (per gm)/plasma (per ml) ratio for the steroid concentrations was above unity in all measurements. The ratio for E2 was highest (isthmus:12, ampulla:8) in the follicular phase and for P (isthmus:26, ampulla:18) during ovulation. Since these highest ratios were attained when plasma steroid concentrations were relatively low they were interpreted as reflections of a maximal receptor contribution.
Adult↗
Lack of association between plasma lecithin: cholesterol acyltransferase concentration and plasma sex hormone concentrations in men.
Plasma lecithin:cholesterol acyltransferase (LCAT) concentration has been shown to be higher in women than in men, suggesting that sex hormones may influence LCAT metabolism. In order to explore this possibility, the associations of plasma LCAT concentration with the concentrations of total, free and protein-bound testosterone, 5 alpha-dihydrotestosterone and oestradiol in plasma, and with total androstenedione concentration in plasma, were examined in 88 men aged 52-67 yr. Total cortisol in plasma was also assayed. No statistically significant correlations were observed between LCAT and androgen or oestrogen concentrations, but a weak positive association was observed between LCAT and plasma cortisol concentration (r = +0.227, p less than 0.05).
Aged↗
Variations in the apolipoprotein AI-CIII-AIV gene region and in lecithin:cholesterol acyltransferase concentration are determinants of plasma cholesterol concentrations.
We have examined the effects of variation in the region of the apolipoprotein (apo) AI-CII-AIV genes, and in plasma lecithin: cholesterol acyltransferase (LCAT) concentration, on plasma cholesterol concentration in 109 unrelated men aged 52-67 yrs. Restriction fragment length polymorphisms (RFLPs) were detected using the restriction enzymes XmnI, PstI and SstI and individuals were divided into groups using information from all three RFLPs in conjunction. Mean plasma concentrations of both total cholesterol and estimated low density lipoprotein-cholesterol differed significantly (P less than 0.0125) among groups of men with different genotypes. Thus, variation in this gene region may be one of the polygenetic factors involved in determining cholesterol levels in the normal population. In the same subjects, plasma cholesterol was also positively correlated with plasma LCAT concentration (r = 0.55, P less than 0.001), due mainly to an increase in the cholesteryl ester content of apo B-containing lipoproteins with increasing LCAT concentration. Since apolipoproteins AI, CIII and AIV have each been shown to modify the activity of LCAT in vitro, the associations of the RFLPs with plasma cholesterol concentration may reflect changes in LCAT activity secondary to qualitative or quantitative changes in one or more of these apolipoproteins.
Aged↗
Evaluating the relationship of metabolic activation system concentrations and chemical dose concentrations for the Salmonella spiral and plate assays.
A factorial experimental design was used within this study to evaluate the influence of multiple metabolic activation system concentrations on the dose-response exhibited by promutagens (indirect-acting mutagens) in the Salmonella spiral and plate assays. The mutagenic activity of the three compounds used spanned three orders of magnitude. The mutagenic activity of the compounds ranged from 10 to 100 revertants/micrograms for acetylaminofluorene (2AAF) to more than 1000 revertants/micrograms for 2-aminoanthracene (2AA). Benzo [a] pyrene (BaP) activity was within an intermediate range (100-1000 revertants/micrograms). During a single experiment, a mutagen was tested in TA100 at 13 doses plus a negative control dose. Each dose was tested at 10 S9 concentrations. The S9 concentrations ranged from 0.1 mg protein/plate to 4 mg protein/plate in the standard plate assay and from 0.25 to 4.90 mg-equivalents in the spiral assay. The spiral Salmonella assay, an automated version of the standard assay, generates dose-response data from a concentration gradient on a single agar plate, thereby providing a straightforward approach to this type of study. This study demonstrates not only that even small differences in S9 concentrations can affect the measurement of mutagenic potency but that S9/compound interactions cannot be generalized through the use of interaction studies. This study also shows that spiral assay data and plate assay data for promutagens cannot be compared directly unless the S9 concentrations for all chemical doses are also comparable.
2-Acetylaminofluorene↗
Predicting blood lead concentrations from environmental concentrations.
A method is presented by which blood lead concentrations can be estimated from environmental concentrations using a multipathway analysis. For the ingestion and dermal uptake pathways the incremental increase in blood lead concentration is estimated as the product of the concentration in the relevant medium, a medium-specific contact rate, and an empirically determined ratio between intake and blood level. The inhalation pathway omits the contact rate and uses a ratio between the concentration in blood and the concentration in air. Model outputs corresponding to various input parameters are presented, and some of these are compared with outputs from the U.S. Environmental Protection Agency's Lead Biokinetic/Uptake model, Lead 5.
Adult↗
Force acting on a dielectric particle in a concentration gradient by ionic concentration polarization under an externally applied DC electric field.
There is a concentration-polarization (CP) force acting on a particle submerged in an electrolyte solution with a concentration (conductivity) gradient under an externally applied DC electric field. This force originates from the two mechanisms: (i) gradient of electrohydrodynamic pressure around the particle developed by the Coulombic force acting on induced free charges by the concentration polarization, and (ii) dielectric force due to nonuniform electric field induced by the conductivity gradient. A perturbation analysis is performed for the electric field, the concentration field, and the hydrodynamic field, under the assumptions of creeping flow and small concentration gradient. The leading order component of this force acting on a dielectric spherical particle is obtained by integrating the Maxwell and the hydrodynamic stress tensors. The analytical results are validated by comparing the surface pressure and the skin friction to those of a numerical analysis. The CP force is proportional to square of the applied electric field, effective for electrically neutral particles, and always directs towards the region of higher ionic concentration. The magnitude of the CP force is compared to that of the electrophoretic and the conventional dielectrophoretic forces.
Journal Article↗
Concentration-dependence of aniline-induced methemoglobinemia in dogs: a derivation of an acute reference concentration.
Four male Beagle dogs per group were head-only exposed to aniline vapor in concentrations ranging from 15.8 to 493.6 mg/m3. Each exposure session was for 4h. Additionally, one group of dogs was both head-only and whole-body exposed to approximately 241 mg/m3 to better appreciate the contribution of dermal uptake on methemoglobin (MetHb) induction. The exposure paradigm chosen was comparable to a dose-escalation type of study, however, providing adequate recovery periods between each exposure session to exclude 'carry-over' effects from one exposure session to another. This was verified by the determination of standard hematology endpoints before and after each exposure session. The time- and concentration-dependence of MetHb was analyzed as the key endpoint. The results of this study show that MetHb was maximal around the end of the 4 h exposure period. Significantly increased MetHb was observed at concentrations equal and above 30.3 mg/m3 at a duration of exposure of at least 60 min. The extent of MetHb formation observed in some hyperventilating dogs suggests that the dosing-rate is important for the outcome of test. Whole body exposed dogs displayed markedly higher MetHb values when compared to head-only exposed dogs. Taking into account the entire concentration-time-effect relationship 23.6 and 20.6 mg/m3 were estimated to be the threshold concentrations to cause 0.8% MetHb following a 4 and 8h exposure period, respectively. The C(n)xt analysis of MetHb formation is consistent with a concentration-dependent restoration kinetics of MetHb suggesting that results from high level exposures cannot readily be extrapolated to low-level exposures. In summary, this study demonstrates that for aniline, an agent known to be bioactivated by a hepatic first-pass metabolism, the rate of delivery and uptake appears to be decisive for the extent of MetHb formation. Carry-over effects related to erythrotoxicity or Heinz body formation were not observed at any exposure level.
Aniline Compounds↗
Lp(a) concentrations are related to plasma lipid concentrations.
Lp(a) concentrations are controlled primarily by genetic variation at LPA, the locus encoding the unique protein apo(a). However, the high heritability is in part a consequence of nearly a 1000-fold range of Lp(a) concentrations found in healthy individuals. As determined by use of siblings genetically identical-by-descent at the LPA locus, there is substantial within-genotype variation in Lp(a) concentrations (ranges averaged about 58% of mean values for 87 sibling groups). This within-genotype variation could affect risk of CVD for nearly 15% of individuals in a population. Furthermore, Lp(a) concentrations are significantly and independently correlated with two key indicators of lipoprotein metabolism, plasma cholesterol and triglyceride concentrations. Taken together, these data suggest that it is both possible and desirable to develop strategies for modifying Lp(a) concentrations.
Alleles↗
Concentrations of endogenous prostaglandin F2alpha in boar semen and effect of a 72-h incubation period on exogenous prostaglandin F2alpha concentration in extended boar semen.
PGF2alpha in semen has been shown to induce uterine contractions, thereby, facilitating sperm transport during fertilization. Previously, we demonstrated that extended boar semen used in artificial insemination does not increase myometrial contractility, but PGF2alpha supplementation did. In this study, we determined the concentrations of endogenous PGF2alpha in pre-sperm and sperm-rich fractions of the boar ejaculate and examined whether changes in the concentration of exogenous PGF2alpha occurred when added to extended boar semen after 72-h incubation at a 17 degrees C storage temperature. Concentrations of endogenous PGF2alpha (n = 10 boars) in pre-sperm and sperm-rich fractions were 69.6 +/- 7.6 and 58.9 +/- 4.4 pg/ml, respectively. No differences were observed in the concentrations of exogenous PGF2alpha in the extended boar semen at 0 h (59.3 +/- 3.3 microg/ml) and after a 72-h incubation period (52.0 +/- 2.1 microg/ml). These results suggest that the concentration of endogenous PGF2alpha in boar semen used for artificial insemination is < 100 pg/ml. The concentration of exogenous PGF2alpha in the extended boar semen did not differ after 72 h, which indicates that it is not metabolized during this period of time.
Animals↗
High concentrations of D-glyceraldehyde-3-phosphate dehydrogenase stabilize the enzyme against denaturation by low concentrations of GuHCl.
It is known that denaturation of D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) in low concentrations of GuHCl, around 0.5 M, at 25 degrees C, leads first to a burst phase drop of activity, followed by slow unfolding with further loss of enzyme activity and aggregation. However, GAPDH at higher concentrations does not increase the aggregation in the slow phase as would be expected but decreases both the inactivation and aggregation of the enzyme instead. It seems that GAPDH at high concentrations protects the enzyme against GuHCl-denaturation. This protection is not a general effect of GuHCl binding by increased protein concentration but specific for GAPDH, as either bovine serum albumin or alpha-lactalbumin does not show any protection at similar concentrations. It is proposed that dissociation of tetrameric GAPDH into dimers in the early phase of denaturation in dilute GuHCl is reversible and further unfolding of the dimer to an aggregation prone species is irreversible and rate-limiting for the unfolding process. High concentrations of the enzyme shift the equilibrium towards the tetramer thus decrease the aggregation of GAPDH in dilute GuHCl.
Enzyme Stability↗
High-Q ultrasonic determination of the critical nanoaggregate concentration of asphaltenes and the critical micelle concentration of standard surfactants.
Asphaltenes are known to be interfacially active in many circumstances such as at toluene-water interfaces. Furthermore, the term micelle has been used to describe the primary aggregation of asphaltenes in good solvents such as toluene. Nevertheless, there has been significant uncertainty regarding the critical micelle concentration (CMC) of asphaltenes and even whether the micelle concept is appropriate for asphaltenes. To avoid semantic debates we introduce the terminology critical nanoaggregate concentration (CNAC) for asphaltenes. In this report, we investigate asphaltenes and standard surfactants using high-Q, ultrasonic spectroscopy in both aqueous and organic solvents. As expected, standard surfactants are shown to exhibit a sharp break in sonic velocity versus concentration at known CMCs. To prove our methods, we measured known surfactants with CMCs in the range from 0.010 g/L to 2.3 g/L in agreement with the literature. Using density determinations, we obtain micelle compressibilities consistent with previous literature reports. Asphaltenes are also shown to exhibit behavior similar to that of ultrasonic velocity versus concentration as standard surfactants; asphaltene CNACs in toluene occur at roughly 0.1 g/L, although the exact concentration depends on the specific (crude oil) asphaltene. Furthermore, using asphaltene solution densities, we show that asphaltene nanoaggregate compressibilities are similar to micellar compressibilities obtained with standard nonionic surfactants in toluene. These results strongly support the contention that asphaltenes in toluene can be treated roughly within the micelle framework, although asphaltenes may exhibit small levels of aggregation (dimers, etc.) below their CNAC. Furthermore, our extensive results on known surfactants agree with the literature while the asphaltene CNACs reported here are one to two orders of magnitude lower than most previously published results. (Previous work utilized the terminology "micelle" and "CMC" for asphaltenes.) We believe that the previously reported high concentrations for asphaltene CMCs do not correspond to primary aggregation; perhaps they refer to higher levels of aggregation or perhaps to a particular surface structure.
Journal Article↗