Disappearance Constants Research Articles

Nutritive value of mixed napier grass (Pennisetum purpureum)- Leucaena (Leucaena leucocephala) silage for ruminants

The objectives of the study were to determine the chemical composition, ruminal degradability, and apparent digestibility of mixed Napier (Pennisetum purpureum) (PP) -Leucaena (Leucaena leucocephala) (LL) silages. Freshly cut Napier and Leucaena were harvested and mixed at 70:30; 50:50; 30:70 ensiled for six weeks. The chemical composition of the fresh forages and the silages were determined using the AOAC (1990) procedures. Dry matter (DM) and crude protein (CP) ruminal degradability were determined by nylon bag technique using three rumen cannulated Bonsmara steers for periods of 0, 6, 12, 24, 48, 72, 96 and 120 hours. DM and CP ruminal degradability kinetics were described by fitting the data on the model P= a+b (1-e−ct) using the neway computer program where a is the rapidly degradable fraction, b is the slowly degradable fraction and c is the outflow rate. Hay supplemented with 25% mixed PP: LL silages was fed to three castrated male Pedi sheep to evaluate apparent digestibility coefficient and N retention. The fresh cut PP had more CP, Fat, and ash, with less OM. Leucaena was richer in most nutrients than Napier. The study indicated the 50:50 silage was the optimal mix to maximize the overall nutritive value. The DM and CP disappearance constants a, b and c were similar for all silages. PP: LL mixing ratio did not affect the DM and CP degradability kinetics of the silages. There was no effect on total dietary intake, apparent digestibility and N retention.

Occurrence and modeling of pharmaceuticals on a sewage-impacted Mediterranean river and their dynamics under different hydrological conditions

The occurrence of 73 representative pharmacologically active compounds (PhACs) was assessed in a sewage-impacted section of the Llobregat River (NE Catalonia, Spain). This Mediterranean river is characterized by flow rate fluctuations strongly influenced by seasonal rainfall. River flow variations increase the potential environmental risk posed by organic micro-pollutants as their concentrations may increase substantially under low flow conditions. Little is known about the transport behavior of emerging contaminants in surface waters once they are discharged from waste water treatment plants (WWTP) into rivers. This research aimed to study the presence and fate of emerging contaminants under different hydrological conditions by sampling two different sites along the river in different seasons. The highest levels of pharmaceuticals were determined during cold and dry periods. The impact of the flow changes on the concentration of the pharmaceuticals in the river was assessed with the relative sensitive coefficients. Due to expected dilution effects, the response of pharmaceuticals to river flow was negative. Only in a few cases, positive relationships between drug concentrations and flow were detected, suggesting an important role of other hydrological phenomena like sediment re-suspension as well as the source of pollutants. To evaluate the role of other factors influencing PhAC concentrations, a plug-flow model was applied to obtain disappearance constants “k” for a set of selected compounds. Erythromycin presented k values of −0.15h−1 in both sites being the compound more efficiently removed from the water column. The k values for ibuprofen, furosemide, enrofloxacin, enalapril, acetaminophen, diclofenac and Ketoprofen were between −0.04 and −0.10h−1 showing less disappearance than erythromycin in the water column. However, other compounds presented k values<0.06, which suggested conservative behavior of these compounds in the water column. This study supports the reliability of the calculated k values for the disappearance of compounds in river waters.

Effects of compost and of bacterial cells on the decontamination and the chemical and biological properties of an agricultural soil artificially contaminated with phenanthrene

Polycyclic aromatic hydrocarbons (PAHs) are highly recalcitrant widespread environmental pollutants. Bioremediation, accomplished by the introduction of PAH-degrading microorganisms (bioaugmentation) and/or by applying additional nutrients (biostimulation) into a contaminated system is a valuable alternative to traditional chemical and physical treatments for the decontamination of PAH-contaminated soils. We investigated on a laboratory scale the fate of phenanthrene (Phe), selected to represent PAHs, when added to a fresh, agricultural soil with no history of PAH contamination. The relative effect of compost (C), applied at two different doses ( C 1 = 0.27 % , and C 2 = 0.83 % , corresponding to 10 and 30 t ha −1 , respectively), and the efficiency of a Phe-degrading bacterial culture inoculated into the soil (S) and soil–compost (S–C1 and S–C2) systems were investigated. Changes in various functionally related properties such as microbial biomass, basal respiration, and soil hydrolases and oxido-reductases activities were measured over time. The variations of the main physical and chemical properties were also monitored. The soil showed an intrinsic capability for degrading Phe, and this was enhanced and stimulated by the lower compost dose (a decrease of the extractable Phe from 70% to about 50% of that initially added, and higher kinetic Phe disappearance constants). A simultaneous, rapid increase of soil respiration and microbial biomass, and higher phosphatase and arylsulphatase activities were measured, suggesting that microbial growth and activity had increased. The inoculation with Phe-degrading bacterial cells strongly accelerated the Phe degradation. After 15 d of incubation, the residual Phe decreased to 10% in S and S–C1 and to zero in S–C2, respectively. No apparent effects were observed for the higher compost dose. Several of the soil properties showed differentiated responses to the presence of the Phe, the compost and/or the exogenous culture. As a general response, soil systems with and without the inoculated cells showed similar trends for several of the measured enzymatic properties (e.g. phosphatase, arylsulphatase, β -glucosidase and urease activities), indicating that the intrinsic soil enzymatic activity was not affected by the exogenous microorganisms. Temporary and permanent changes were observed for several of the properties investigated, thereby providing useful information on the impact of Phe on soil metabolic activity.

Evaluating degradation rates of chlorinated organics in groundwater using analytical models

The persistence and fate of organic contaminants in the environment largely depends on their rate of degradation. Most studies of degradation rate are performed in the lab where chemical conditions can be controlled precisely. Unfortunately, literature values for lab degradation studies often are orders of magnitude higher than for field-generated studies, calling into question the relevance of lab-generated values for characterizing the persistence of organic contaminants in the environment. Complicating analysis of this ostensible disparity between lab and field degradation values, field-generated values often do not account for effects of adsorption. Modeling with a newly derived analytical solution for first-order degradation coupled with advective losses and adsorption to solve for degradation constants is insensitive to uncertainties in field properties. Application to field data shows that accounting for advection and adsorption greatly affects the value of calculated degradation constants compared to disappearance constants, which do not account for these phenomena. In fact, degradation constants, calculated using these analytical solutions and field data, are in the range reported for lab-generated data. Using these analytical solutions, for the sulfate-reducing field conditions documented for this site, perchloroethene, trichloroethene, 1,1,1-trichloroethane, 1,1-dichloroethane, and chloroethane all degraded with half-lives ranging from 5 to 115 d. Consistent with other studies of sulfate-reducing conditions, cis-1,2-dichloroethene did not chemically degrade at a measurable rate. When nonaqueous phase 1,1-dichloroethane is present, down-gradient concentrations vary in an annual sinusoidal pattern, apparently because of seasonal variation in dilution from groundwater recharge.

The reaction of copper(II) complexes of macrocyclic dioxotetraamines with hydroxyl free radical—A kinetic study by pulse radiolysis

The copper(II) complexes of three dioxotetraamines were oxidized rapidly by hydroxyl free radical .OH produced by pulse radiolysis at pH 7.4. The formation and disappearance of copper(III) complexes were followed by electronic spectroscopy. The formation of Cu II complexes obeyed pseudo-first order reaction and their disappearance obeyed first order reaction. The oxidation rates of Cu II complexes by .OH have the following sequence: [Cu(npt)] > [Cu(dt)] ≈ [Cu 2(bdt)]. The formation and disappearance constants are in the following range: k t = 1.73 × 10 10−1.19 × 10 10, k d = 3.99 × 10 3−1.24 × 10 4.

Pregnancy in a patient with homozygous familial hypercholesterolemia undergoing low-density lipoprotein apheresis by dextran sulfate adsorption

Pregnancy and delivery in homozygous familial hypercholesterolemic (HFH) patients is extremely rare. We describe the case of a woman with HFH treated with low-density lipoprotein (LDL) apheresis by dextran sulfate adsorption who became pregnant and reached delivery uneventfully. LDL apheresis was performed biweekly, and lipoprotein analyses in pre-apheresis samples showed progressive increases in triglyceride, total cholesterol, LDL cholesterol, and apolipoprotein (apo) B plasma concentrations. The fractional catabolic rate (FCR) for LDL cholesterol, as estimated by the first-order disappearance constants ( k values) of the recovery of LDL cholesterol concentration to basal values after each apheresis session, increased more than threefold from week-24 to week-4 (labor is considered as time 0). After delivery, basal values were recovered, but normalization was slower for LDL cholesterol than for the other lipidic parameters. High-density lipoprotein (HDL) showed a different pattern: HDL 3 remained stable throughout gestation, whereas HDL 2 cholesterol and apo A-I had a maximum at midgestation, then declined, and finally increased again at late gestation. With the exception of this latter increase of HDL 2, all the other changes in lipoprotein concentrations during pregnancy and postpartum were similar to those found in healthy women. Thus, LDL apheresis does not interfere with physiologic adaptations of lipoprotein metabolism during pregnancy in HFH patients.

Chronic chloroquine treatment enhances insulin release in rats

The effects of chronic chloroquine treatment on intravenous glucose tolerance, and the plasma insulin response to intravenous glucose were studied in rats. Plasma glucose disappearance constants ( K g) were significantly greater (6.2 ± 0.5 %min −1) than in corresponding controls (3.7 ± 0.4 %min −1, P < 0.001). This improved glucose tolerance was associated with significantly higher plasma immunoreactive insulin levels in response to glucose injection. Islets isolated from rats treated with chloroquine showed significantly enhanced ( P < 0.05) insulin release when incubated with 16.7 mM glucose but not with lower glucose concentrations (3 and 8 mM). Pre-incubation of islets with streptozotocin (0.05–1.5 mg/ml) produced a dose-dependent reduction in glucose-stimulated insulin secretion which was not modified in islets from chloroquine-treated rats. The concentration of chloroquine in the pancreas increased rapidly during administration and reached a value of 20.2 ± 0.7 μg/g (fresh weight) after 20 weeks of treatment. It is concluded that chronic chloroquine treatment results in an improved glucose tolerance associated with an enhanced glucose-induced insulin secretion. Although earlier work showed chloroquine to reduce the severity of diabetes induced subsequently with streptozotocin, the present study shows that such an amelioration was not due to a protective effect against the β-cell cytotoxic action of streptozotocin.

Effect of HELP‐LDL‐apheresis on serum concentrations of human lipoprotein(a): kinetic analysis of the post‐treatment return to baseline levels

In addition to LDL, Lp(a) can be quantitatively eliminated from plasma in an extracorporeal LDL-apheresis procedure based on precipitation with heparin at pH 5.12. The rates of return of post-apheresis Lp(a) and LDL-cholesterol concentrations to baseline levels were investigated in six individuals with familial hypercholesterolaemia (one homozygote, five heterozygote) and one normolipaemic individual. The first-order disappearance constants (kappa) were derived for LDL and Lp(a) according to Apstein et al. The kappa values for LDL in the homozygous FH and the normolipaemic individual were 0.082 and 0.43 respectively while the heterozygous FH patients had kappa values intermediate between the two (median 0.231; range 0.116-0.261). The first-order disappearance constants of Lp(a) did not correlate with those of LDL. The homozygous FH and normolipaemic individuals had Lp(a) kappa values of 0.158 and 0.199 respectively; the corresponding values in the heterozygous FH patients were: median 0.142; range 0.045-0.179.

Assessment of the cytochrome P-448 dependent liver enzyme system by a caffeine breath test.

[1-Methyl-14C], [3-Methyl-14C] and [7-Methyl-14C] caffeine were used to investigate demethylation in control rats, and in rats pretreated with phenobarbital or 3-methylcholanthrene, by a 14CO2-exhalation test. Compared to controls, pretreatment with phenobarbital did not enhance demethylation of any of the labelled caffeines. In contrast, induction by 3-methylcholanthrene, presumably of cytochrome P-448, resulted in highly significant increases in peak 14CO2 exhalation rates, 14CO2 disappearance constants and areas under the exhalation rate - time curves. Based on these results, [7-methyl-14C] and [3-methyl-14C] caffeine were chosen for assessing the feasibility of a caffeine breath test in man, using 5 normal volunteers and 2 patients with compensated liver cirrhosis. 14CO2 exhalation curves in cirrhotics were clearly different from those in normal volunteers, being characterised by a slower rise and a lower specific activity of exhaled 14CO2. Since the variability of the levels of the specific activity in subjects with normal livers suggested the influence of extraneous factors, a second group of normal volunteers, smokers and nonsmokers, was investigated. With either labels, the average 14CO2 exhalation rate was doubled in smokers. From these studies in rats and preliminary results in man it is concluded that specifically labelled caffeine is a suitable and promising substrate for studying demethylation by breath analysis. Presumably, caffeine represents a safe and sensitive indicator of the activity of the cytochrome P-448 system.

Selection of a suitable circulatory model for the plasma clearance and distribution of cardiac enzymes in the dog.

This study concerns the existing controversy about the validity of one-vs two-compartment models for the distribution of intravenously injected enzymes in the dog. It is shown that infusion of enzyme at a constant rate permits direct calculation of enzyme clearance constants, independently of the specific model used. Enzyme preparations were obtained by leakage of enzymes from heart tissue under hypoxic conditions. The values for the plasma clearance constants k of creatine kinase (CK) and aspartate aminotransferase (AST) are 0.36 ± 0.030 h−1 and 0.21 ± 0.014 h−1 respectively (mean ± SE, n = 8). These values are compared with clearance rates as estimated from a bolus injection of enzyme given 90 min before the infusion was started. For both enzymes the values of k as estimated from the infusion equal the apparent disappearance constants kd obtained from the preceding bolus injections. From these experiments it is concluded that plasma clearance of CK and AST is adequately described by a one-compartment model. In 10 experiments plasma clearance curves after bolus injections were sampled over 8 h. Disappearance of AST was strictly mono-exponential, while for CK a slight biphasic effect was observed in five out of ten cases resulting into improved double-exponential fits. It is concluded that this effect is not due to exchange of enzyme with an extravascular pool but is caused by a fraction of enzyme with a slightly higher elimination rate. This phenomenon is illustrated by showing that AST also shows biphasic disappearance upon injection of an enzyme preparation obtained by mechanical disruption of cells. Individual and day-to-day variations in k values obtained for CK and AST do not show any correlation. This suggests independent clearance mechanisms for both enzymes.

Disappearance constants of carbaryl from streams contaminated by forest spraying.

Disappearance constants of carbaryl from streams contaminated by forest spraying.

A comparison of intravenous and oral glucose tolerance tests in the dog

Glucose and insulin levels were measured at various intervals after oral and intravenous administration of glucose to 12 normal adult crossbred dogs. The pre-test diet, starvation period and time of testing were all standardised. The glucose (1 g/kg) was delivered as a 50 per cent solution for the intravenous test and in a constant volume of 50 ml for the oral test. A two way analysis of variance demonstrated significantly greater variability with the oral test. Because of consistency and ease of parameter calculation, it was thought that the intravenous glucose tolerance test would be more accurate for assessing glucose intolerance. An intravenous glucose tolerance test was performed under similar conditions on 12 diabetic dogs and the glucose disappearance constants for the normal and diabetic animals compared for various periods. The disparity between normal and diabetic animals was greatest over the 10 to 60 min period (eight samples). Furthermore, when a three sample (10, 20 and 40 min) subset of this period was used a similar difference was obtained. With either the 10 to 60 min period or the 10, 20, 40 min subset, a glucose disappearance value of 2 or less in a dog indicates glucose intolerance.

Body disappearance and liver mean transit time of 99m-Tc-diethyl-IDA.

The body disappearances and the liver mean transit times of a hepatobiliary tracer, 99mTc-diethyl IDA, were measured from 100 cholescintigraphies of 98 patients. Fifteen patients had no hepatobiliary disease; their mean body disappearance was 6.6, SD 1.1%/min, and mean liver mean transit time 32, SD 19 min. The values within 2 SDs, disappearance greater than or equal to 4.4%/min and mean transit time less than or equal to 70 min, were used as reference values. Disappearance constants below 4.4%/min were observed 29% and mean transit times exceeding 70 min in 49% of the examinations performed on patients with some hepatobiliary abnormality. The calculated parameters were compared with the levels of serum bilirubin and ASAT. Disappearance constants below 4.4%/min were seen in 33% and mean transit times exceeding 70 min in 55% of the patients who had either abnormal serum bilirubin or ASAT due to a hepatobiliary disease. The correlation between the serum bilirubin and the disappearance was -0.13, and between ASAT and body disappearance it was -0.28. The corresponding correlation coefficients of serum bilirubin and ASAT with the liver mean transit times were 0.33 and 0.44. Long mean transit times in relation to bilirubin and ASAT were seen in some acute cases. Short mean transit times in relation to bilirubin and ASAT were seen with falling serum levels of the latter.

Effect of hematocrit on the washout of xenon and iodantipyrine from dog myocardium.

The rates of washout of 133Xe and 131I-iodoantipyrine from the myocardium into the coronary sinus blood were determined over a wide range of hematocrits after simultaneous injection of the isotopes into the left anterior descending coronary artery of dogs. The ratio of the monoexponential disappearance constants (kX/kI), which is a measure of the ratio of the dynamic blood-tissue partition coefficients (lambdabIX/lambdabtI), increases linearly with hematocrit. This dynamic lambdabt ratio has almost the same relationship to hematocrit as the static lambdabt ratio. By the use of appropriate hemotocrit-specific lambdabt values, we found that simultaneous blood flows calculated from the two indicators with different disappearance constants showed excellent agreement. If this hematocrit-dependent alteration in indicator partitioning is neglected, blood flow measurement in the dog with 133Xe washout may introduce an error of approximately 1.15% per unit hematocrit deviation from the normal value (taken as 45%), whereas blood flow measurements with 131I-iodanatipyrine washout had negligible errors.

Serum and Urine Levels of Ethchlorvynol in Man

Serum and urine levels of ethchlorvynol were determined by gas chromatography using electron-capture detection. The method is sensitive to 0.25 mcg./ml. and reproducible within 2% relative standard deviation. In 25 hr., 0.025% of the total dose is excreted unchanged or as the glucuronide. Peak serum levels of 2.5, 6.5, or 8.0 mcg./ml. are seen at 1 hr. after administration of 200,500, or 750-mg. capsules, respectively. The decline of the serum levels is biphasic, with disappearance constants of 0.5 and 0.03 hr.−1. When the data are interpreted in terms of a two-compartment model, therate constant for elimination is calculated to be 0.13 hr.−1. The ratio of the amount of ethchlorvynol in the tissue compartment to that in the central compartment is 3.5:1.

89 Hypoglycemia in Infants with Erythroblastosis Fetalis

Hyperplasia of the Islets of Langerhans is usually found in fetuses in infants who die as a result of erythroblastosis fetalis (EF) and the pancreas contains levels of insulin comparable to those found in infants of diabetic mothers (IDM). The clinical counterpart of these observations, hypoglycemia, is believed to occur rarely if at all in infants with EF. During the last 18 months we have observed hypoglycemia (< 30 mg/100 ml in term infants; < 20 mg/100 ml pre-term) in 11 infants. Borderline levels have occurred in 2 others. Five of the infants developed hypoglycemia prior to exchange transfusion (ET). Recently 16 consecutive infants with moderate to severe EF have had frequent blood glucose measurements following ET. 6 (30 %) developed symptomatic hypoglycemia with borderline values in 2 others. 9 infants had multiple measurements of blood glucose in the 3 h period following ET and 4 of these had simultaneous measurements of serum immuno active insulin. Serum insulin was elevated in all 4 infants. Glucose disappearance constants (Kt) were calculated for the first hour following ETand compared to Kt values for normals and IDM following IV glucose tolerance tests. The infants with EF who developed hypoglycemia had significantly greater Kt values than did the normals; their values approximated IDM. Because of the necessity for prompt treatment, blood glucose should be measured frequently in infants with EF both after birth and after ET. Intravenous glucose or fructose should be effective in prevention of hypoglycemia. (APS)

Rate of exchange of sodium and potassium between amniotic fluid and maternal system.

SummaryThe exchange rate of sodium to and from the amniotic fluid was determined by the simultaneous application of sodium-22 and sodium-24. This exchange rate, in opposite directions, was found to be 15 and 16 mEq. of sodium per hour, respectively. The transfer rate of hydrogen, sodium, and potassium from the amniotic fluid to the maternal system was determined by the simultaneous application of tracers for each of these elements. The disappearance constants for sodium and potassium were found to be nearly equal, indicating that the same percentage of these elements is exchanged per unit of time, while that for deuterium was found to be 5 times greater. The exchange rates were calculated as 31.9 moles of water, .014 mole of sodium, and .00041 mole of potassium per hour. It is concluded that the water and electrolytes of the amniotic fluid are in dynamic equilibrium with maternal plasma, each exchanging at its own characteristic rate.