Effects of MEK on kinetics of n-hexane metabolites in serum

The neurotoxicity of n-hexane is thought to be caused ultimately by 2,5-hexanedione (2,5-HD), one of the n-hexane metabolites. The potentiation of n-hexane neurotoxicity by co-exposure with MEK, therefore, is suspected to be related to kinetics of 2,5-HD in blood. To clarify the kinetics of n-hexane metabolites in the mixed exposure of n-hexane and MEK, rats were exposed to 2000 ppm n-hexane or a mixture of 2000 ppm n-hexane and 2000 ppm MEK, and the time courses of serum n-hexane metabolites were determined. 2,5-HD in serum increased until 2 h after the end of exposure, when serum 2,5-HD concentration reached a peak of 16.35 micrograms/ml in the n-hexane-alone group. In contrast, 2,5-HD in the mixed exposure group increased much more slowly during and after exposure than in the n-hexane-alone group. It reached a peak of 2.12 micrograms/ml at 8 h after the end of exposure. Serum MBK, a precursor of 2,5-HD in the co-exposure group, was about half in the n-hexane-alone group during exposure. However, MBK decreased more slowly in the co-exposure group than in the n-hexane-alone group after the end of the exposure. The results suggest that co-exposed MEK might inhibit oxidation of n-hexane and decrease clearance of n-hexane metabolites. Co-exposed MEK did not increase serum 2,5-HD, which was considered a main neurotoxic metabolite. Therefore the enhancement of neurotoxicity could not be attributed to increased serum 2,5-HD in the co-exposed group.(ABSTRACT TRUNCATED AT 250 WORDS)

[Electrophysiologic study of ischemic ventricular arrhythmia]

Epicardial composite electrode and isochronal mapping were used in this study to detect ventricular late potentials and ventricular activity sequence during sinus rhythm and ventricular tachycardias. 20 dogs were studied before and during acute ischemia induced by coronary artery ligation, 11 dogs 3-7 days after two-stage ligation of the left anterior descending coronary The effect of lidocaine and verapamil on VLP and reentrant ventricular arrhythmias was studied. The results demonstrated that: (1) Ventricular arrhythmias occurred right after ligation and 3-7 days later after ligation were related to the reentry in infarct myocardia zone; (2) The inhomogeneous conduction and dispersive refractory period provided a suitable milieu for reentry; (3) Reentrant excitation always occurred in a figure 8 configuration and delayed depolarization and continuous activation were reflected as VLPs at composite electrode; (4) Lidocaine in therapeutic dose prolonged the VLPs and interval of V-VLP. The effect of lidocaine on the ischemic zone was directly related to its ability to abolish reentrant ventricular arrhythmias; (5) Verapamil shortened the VLPs and interval of V-VLP, so the action of slow-response action potentials could not be excluded. Further study should be performed in order to demonstrate the precise mechanism of VLP.

Changes in urinary n-hexane metabolites by co-exposure to various concentrations of methyl ethyl ketone and fixed n-hexane levels

To make clear how the n-hexane metabolism is modified by co-exposure with MEK, rats were exposed to various concentrations of MEK mixed with a fixed concentration of n-hexane. Twenty-four male Wistar rats were divided into four equal groups. Each group was exposed for 8 h to 2000 ppm n-hexane, 2000 ppm n-hexane plus 200 ppm MEK, 2000 ppm n-hexane plus 630 ppm MEK and 2000 ppm n-hexane plus 2000 ppm MEK, respectively. Free metabolites and the sum of free and conjugated metabolites of n-hexane were analyzed by gas chromatography. The main metabolite was 2-hexanol during the exposure and 2,5-hexanedione (2,5-HD) after the exposure in any group. The main metabolites, 2-hexanol and 2,5 HD, decreased in inverse proportion to the co-exposed MEK concentrations. The results suggest that augmentation of n-hexane neurotoxicity by MEK co-exposure could not be explained only by 2,5-HD. In addition, 2,5-HD is recommended as an index for biological monitoring of n-hexane exposure. However, one should be careful to evaluate the exposed n-hexane concentration by urinary 2,5-HD, because n-hexane metabolism could be largely modified by co-exposure with MEK.

A porcine rotavirus strain with dual VP7 serotype specificity

Porcine rotavirus MDR-13, which on original isolation showed a two-way antigenic relationship with human rotavirus RV-3, shows VP7 relationships with serotype G5 as well as G3 viruses upon gene reassortment. Analysis of porcine MDR-13 and the MD-UK reassortant revealed marked nucleotide and amino acid similarity of VP7 genes of these viruses with those of both serotype G3 and G5 viruses. Evolution of such a strain, possibly by sequential mutations in the VP7 gene, is discussed.

Expression in yeast of the T-urf13 protein from Texas male-sterile maize mitochondria confers sensitivity to methomyl and to Texas-cytoplasm-specific fungal toxins

The mitochondrial gene T-urf13 from maize (Zea mays L.) with Texas male-sterile (T) cytoplasm codes for a unique 13 kd polypeptide, T-URF13, which is implicated in cytoplasmic male sterility and sensitivity to the insecticide methomyl and to host-specific fungal toxins produced by Helminthosporium maydis race T (HmT toxin) and Phyllosticta maydis (Pm toxin). A chimeric gene coding for T-URF13 fused to the mitochondrial targeting peptide from the Neurospora crassa ATP synthase subunit 9 precursor was constructed. Expression of this gene in the yeast Saccharomyces cerevisiae yielded a polypeptide that was translocated into the membrane fraction of mitochondria and processed to give a protein the same size as maize T-URF13. Methomyl, HmT toxin and Pm toxin inhibited growth of yeast cells expressing the gene fusion on medium containing glycerol as sole carbon source and stimulated respiration with NADH as substrate by isolated mitochondria from these cells. These effects were not observed in yeast cells expressing T-URF13 without a targeting peptide. The results show that T-URF13 is sufficient to confer sensitivity to methomyl and the fungal toxins in a heterologous eukaryotic system, and suggest that mitochondrial localization of T-URF13 is critical for these functions.

Ontogenesis of the electroretinogram in a precocial mammal, the guinea pig (Cavia porcellus)

1. Ontogenesis of the electroretinogram, the mass electrical response of the retina to flash light stimuli, was studied in the guinea pig (Cavia porcellus), a precocial species with visual function at birth. 2. a-Wave components, b-wave, oscillatory potentials, slow PIII, and c-wave responses to flash stimuli developed between 55 and 64 days of gestation (full term is 68-69 days). 3. a-Waves attributable to photoreceptor functions were fully mature at 60 days. 4. ERG development lagged behind the reported critical milestones in retinal development; its prenatal onset indicates that no history of light entrainment is required for initiation of a mature ERG response.

Airway pressure-volume curve estimated by flow interruption during forced expiration

We attempted to estimate the pressure-volume characteristics of airways downstream from the choke point when the airflow was abruptly interrupted during forced expiration. The change of gas volume of the downstream segment after interruption could be estimated by multiplying the maximum flow (Vmax) immediately before interruption by the interruption time because the Vmax is maintained for a short period after airflow interruption at the mouth, as described in our previous report (J. Appl. Physiol. 66: 509-517, 1989). For the pressure of the downstream segment, we used the mouth pressure itself. Airway compliance, a slope of the pressure-volume curve, was measured in an airway model in eight normal subjects, in six patients with chronic obstructive pulmonary disease (COPD), and in one patient with tracheobronchopathia osteochondroplastica. Airway compliance was 0.96 ml/cmH2O in normal subjects and 2.49 ml/cmH2O in COPD patients. This difference of airway compliance was believed to be caused by the longitudinal expansion of the downstream segment and changes in the properties of the airway wall.

An acidic fibroblast growth factor stimulates DNA synthesis, inhibits collagen and alkaline phosphatase synthesis and induces resorption in bone

We have examined the effects of an acidic fibroblast growth factor (aFGF) on bone cell growth and differentiation and on osteoclastic resorption using rat fetus organ cultured calvariae and long bones, respectively. Low concentrations of this aFGF stimulated DNA synthesis (1.28 ng/ml) and inhibited collagen formation (1.28 ng/ml) and alkaline phosphatase activity (0.64 ng/ml) in the isolated calvariae. The inhibition of collagen synthesis was independent of the aFGF's mitogenic effect, and was evident in periosteum-containing and periosteum-free bones, pointing to osteoblasts as the aFGF-responsive cells. Our preparation of aFGF enhanced resorption in the long bones by a calcitonin-inhibitable mechanism. PGE2 release accompanied and indomethacin prevented the enhancement of resorption. By contrast, indomethacin did not block the stimulation of DNA and collagen synthesis caused by our aFGF. These results indicate that our aFGF exerts a PGE2-independent effect on DNA synthesis and collagen synthesis and a PGE2-dependent effect on resorption in bone tissue in vitro.

Subcellular localization of an intermediate filament protein and its mRNA in glial cells

Eucaryotic mRNAs are generally localized in the cell body, where most protein synthesis occurs. We have found that mRNAs encoding the glial intermediate filament protein are spatially distributed in the glial cell cytoplasm close to the location of the glial filaments. Whereas the glial filament protein mRNA was located predominantly in the distal process, actin mRNA was found almost exclusively in the apical portion of the glial cell. This pattern of mRNA localization might provide a mechanism for synthesis of proteins in specific subcellular compartments by mRNA translation locally.

Comparative sequence analysis of VP7 genes from five Australian porcine rotaviruses

The genes coding for the rotavirus major neutralizing protein, VP7, from 5 Australian porcine rotaviruses representing glycoprotein (i.e. VP7 or G) serotypes 3, 4, and 5, were sequenced. The genes were each 1,062 nucleotides long with two long open reading frames for proteins of either 326 or 297 amino acids and containing only one potential glycosylation site at amino acid position 69. When compared to the corresponding genes of human viruses, the porcine genes showed very high nucleotide and deduced amino acid homology. Sequence comparison also revealed that Australian porcine rotaviruses of G serotype 4 and 5 were similar to the corresponding porcine strains found in the U.S.A. and U.K., while G serotype 3 and 4 porcine rotaviruses were closely related to human G serotype 3 strain, RV-3 and serotype 4 strain, ST-3, respectively. These Australian rotavirus VP7 sequences were found to correlate with serological data we reported previously.

[Electrophysiologic studies on reentrant ventricular arrhythmia in the late myocardial infarction period]

The mechanisms of reentrant ventricular tachycardia were studied in canine post-infarction model. In 15 dogs that weighed 10-20 kg, the anterior descending coronary artery was ligated. 3 to 7 days after coronary artery occlusion, the dogs were reoperated to set up a composite electrode or a patch electrode with 32 bipolar electrodes. The composite electrode was utilized to record ventricular late potentials (VLPs) from the epicardial surface of the infarction zone (IZ) and adjacent normal zone (NZ). The bipolar electrodes were used to record the epicardial isochronal maps. 16 bipolar electrodes were placed over the area of infarction and its bordering zone and the other 16 bipolar electrodes were distributed over the remaining surface of the ventricle. Reentrant ventricular tachycardias were induced by programmed electrical stimulation. The VLPs and epicardial isochronal activation were recorded by SC-16 oscillograph and computerized mapping system during sinus rhythm and programmed stimulation. The experiments showed; 1) VLPs were demonstrated in 11 of the 15 dogs (73.3%) during programmed stimulation. 2) The reentrant circuit has a characteristic figure-8 configuration in the form of two circulating wave-fronts around arcs of functional conduction block that coalesce into a slow commun reentrant wave-front. One of the two synchronous circuits traveled clockwise and the other counter-clockwise. 3) VLPs represent a delayed depolarization at the ischemic myocardium, where the impulse conducts slowly in the reentrant circuit. It is clear that the present study may increase the understanding of the mechanism of ventricular arrhythmias in the late myocardial infarction period.

Effects of chronic n-hexane exposure on nervous system-specific and muscle-specific proteins

Two kinds of nervous system-specific and muscle-specific proteins, enolase and S-100 protein, were quantitatively determined in peripheral nerves and skeletal muscles of rats chronically exposed to a neurotoxic solvent - n-hexane. Three groups of animals were exposed to n-hexane vapor at three different solvent concentrations (500 ppm, 1200 ppm, 3000 ppm) for 12 h/day, 7 days/week for 16 weeks. The body weight gain and motor nerve conduction velocity (MCV) in exposure groups show progressively concentration-dependent decreases compared to control values. Histopathological examination also demonstrates the degeneration of peripheral nerves in 3000 ppm- and 1200 ppm-exposed rats. The significant decrease in the amount of S-100 protein in peripheral nerves was observed not only in the high level exposure groups (3000 ppm and 1200 ppm), but also in the lowest level group (500 ppm), although the MCV and morphological examination remained unchanged at this level. In addition, the muscle-specific S-100 protein in 3000 ppm exposed rats' soleus also displayed a significant reduction. In contrast to this, however, enolase isozymes were not significantly changed by either dosage level in both nervous tissue and skeletal muscle. The experiment suggests that beta- and alpha-S-100 proteins which are specifically localized in nervous system and muscles, respectively, are more vulnerable than enolase isozymes under treatment with n-hexane, and may possibly serve as a specific indicator to evaluate the neurotoxic effects. Further research would be worthwhile to elucidate the role of the specific S-100 protein in evaluating the neurologic damage induced by various industrial chemicals.

Antimalarial and toxic effect of triple combination of pyronaridine, sulfadoxine and pyrimethamine

The triple combination of pyronaridine, sulfadoxine and pyrimethamine which has been proven to be efficient in delaying emergence of drug resistance of rodent malarial parasites was further studied for potential application to malaria control. The antimalarial effect of the triple combination on Plasmodium berghei ANKA-infected mice and the toxic effects in mice and rats were additive. A single dose of pyronaridine 500 mg in combination with sulfadoxine, 1000 or 1500 mg, and pyrimethamine, 50 or 75 mg, given to 72 acute falciparum malaria patients resulted in a 100% cure rate with nil or mild side effects, and no recrudescence of asexual parasite over 4-week follow-up. Preliminary experiments on the drug effect on sporogony showed that the drug combination at the dose used could not completely interrupt the sporozoite formation although many retarded oocysts were found.

A sensitive, inexpensive method for determining minute quantities of lipase activity

We describe a sensitive and reproducible lipase assay based on the binding of 63Ni to fatty acid. This method can detect down to 1 nmol of fatty acid per milliliter of solution. It has been adapted for measuring low concentrations of lipoprotein lipase and hepatic triacylglycerol lipase. Furthermore, in the presence of tritiated triolein, the method is insensitive to radiolabel interference, even when the fatty acid is labeled.