Biomedical subjects

S Padilla

Publications and source records attributed to S Padilla.

At least 73 records · Page 4Linked to original sources

PubMed1996

Quantitative, video-based histochemistry to measure regional effects of anticholinesterase pesticides in rat brain.

Acetylcholinesterase histochemistry was coupled to inexpensive and widely available apparatus for video microscopy and densitometry to study enzyme activity and inhibition in different parts of the rat brain. Quantitative histochemistry, under properly defined conditions, yielded an output that increased linearly with incubation time and section thickness and was a smooth hyperbolic function of substrate concentration. The time-course of staining after in vivo exposure to eserine revealed no sign that carbamate-induced cholinesterase inhibition was readily reversed in vitro. Brains from rats treated either with a carbamate or an organophosphate anticholinesterase pesticide showed significant regional variation in cholinesterase inhibition. The histochemical data corresponded well with data from biochemical assays of acetylcholinesterase activity (overall correlation coefficient of absolute values, r = 0.95). Also, a comparison of assay types by two-way analysis of variance showed no significant main effect. These results support the conclusion that video-based histochemistry is suitable for detailed studies of developmental and toxicological influences on cholinesterases in multiple microscopic regions of the rat brain.

Animals↗

PubMed1996

Factors in standardizing automated cholinesterase assays.

A scientific panel assembled by the U.S. Environmental Protection Agency (EPA) determined that variability in cholinesterase (ChE) activities in the agency's pesticide/animal study database likely was due to a lack of accepted guidelines for ChE methodology. A series of trials was held in which participating laboratories measured ChE activity in blood and brain samples from untreated and pesticide-treated rats using a colorimetric assay method. The degree of inhibition of ChE activity in plasma and brain samples compared to controls was consistent among most of the laboratories. The ChE activity in erythrocyte samples differed more between laboratories due to a high blank, low erythrocyte AChE activity and hemoglobin absorption at the wavelength of the assay. Strategies are suggested for minimizing the variability of ChE activity in hemoglobin-rich samples.

Acetylcholinesterase↗

PubMed1996

Maturational differences in chlorpyrifos-oxonase activity may contribute to age-related sensitivity to chlorpyrifos.

Chlorpyrifos (CPF), a commonly used cholinesterase-inhibiting insecticide, is lethal at much lower doses to young animals than adults. To explain this higher sensitivity in younger animals, we hypothesized that young rats have less chlorpyrifos-oxonase (CPFOase) activity than adults. To test this hypothesis, CPFOase activity was measured in the brain, plasma, and liver of male, postnatal day 4 (PND4) and adult (PND90) Long-Evans rats. CPFOase is biochemically defined as a Ca(2+)-dependent A-esterase that hydrolyzes chlorpyrifos-oxon (CPFO), the active metabolite of CPE. No brain CPFOase activity was detected at either age. Plasma and liver CPFOase activities were markedly lower at PND4 compared to adult: PND4 plasma and liver CPFOase activities were 1/11 and 1/2 the adult plasma and liver activities, respectively. Because the Km of CPFOase activity was high (i.e., 210-380 microM), it was important to determine if this CPFOase activity could hydrolyze physiologically relevant concentrations (i.e., nM to low microM) of CPFO. This was accomplished by comparing the shifts in the tissue acetylcholinesterase (AChE) IC50 for CPFO in the presence or absence of CPFOase activity. One would expect an increase in the "apparent" IC50 if CPFOase hydrolyzes substantial amounts of CPFO during the 30 minutes the tissue is preincubated with the CPFO. In the adult, both plasma and liver AChE apparent IC50 values were higher in the presence of CPFOase activity, suggesting that the CPFOase in those tissues was capable of hydrolyzing physiologically relevant concentrations of CPFO within 30 minutes. In young animals, however, there was less of a shift in the IC50 curves compared to the adult, confirming that the young animal has less capacity than the adult to detoxify physiologically relevant concentrations of CPFO via CPFOase.

Acetylcholinesterase↗

PubMed1996

Inhibition of rat brain phosphatidylinositol-specific phospholipase C by aluminum: regional differences, interactions with aluminum salts, and mechanisms.

We have shown previously that aluminum chloride (AlCl3, 10-500 microM) inhibits hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phosphatidylinositol-specific phospholipase C (PI-PLC) in a concentration-dependent manner. In the present study, we characterize further the effects of aluminum on PI-PLC. A comparison of different brain regions and liver revealed varying basal PI-PLC specific activities, as well as differential susceptibility to inhibition by 100 microM AlCl3. The hippocampus had the highest specific activity of PI-PLC, followed by striatum, frontal cortex, cerebellum, and liver. PI-PLC inhibition by 100 microM AlCl3 was greatest in the liver, followed by cerebellum, hippocampus, cortex, and striatum. Moreover, 100 microM AlCl3 or aluminum lactate (Al (lac)) were similarly effective at inhibiting PI-PLC activity in rat cortical tissue. Addition of AlCl3 (100 microM) decreased PI-PLC activity at CaCl2 concentrations ranging from 0 to 2 mM; however, AlCl3 did not affect the shape of the calcium concentration curve, suggesting that aluminum does not inhibit PI-PLC activity by interference with the cofactor, calcium. AlCl3 (100 microM) did inhibit rat cortical PI-PLC hydrolysis of PIP2 in a competitive manner. These results demonstrate some regional/tissue differences in PI-PLC activity and its sensitivity to aluminum, and effects of AlCl3 and Al(lac) consistent with the effects previously noted in PI turnover in brain slices. Furthermore, our results suggest that competitive inhibition of PLC-mediated PIP2 hydrolysis by aluminum is a potential mechanism by which aluminum may cause the disruptions phosphoinositide signaling which have been reported following in vivo and in vitro exposure.

Aluminum Chloride↗

PubMed1996

The impact of dose rate on the neurotoxicity of acrylamide: the interaction of administered dose, target tissue concentrations, tissue damage, and functional effects.

Health agencies are often required to predict the effects of long term low level exposure in humans based on annual data involving short-term high-level exposures. Uncertainties in extrapolation can be, in part, based on potentially different mechanism associated with different exposure scenarios. This study evaluated the adequacy of short-term exposures to acrylamide for predicting neurotoxicity produced by long-term exposures. The neurotoxic effects of acrylamide (ip) were assessed in rats after acute (0-150 mg/kg), 10-day (0-30 mg/kg), 30-day (0-20 mg/kg), and 90-day (0-10 mg/kg) exposures. Behavioral endpoints included motor activity, grip strength, and the acoustic startle response. Histological examination of sciatic nerve and spinal cord was also performed. Internal and target tissue doses were estimated by measurement of the concentration of acrylamide in serum and sciatic nerve. Functional and pathological results demonstrated that the effects of acrylamide depended on the dose rate and that the neurotoxicity of acrylamide was less than that predicted by a strict dose x time relationship. Behavioral endpoints showed both qualitative and quantitative changes as a function of dose rate. Recovery of behavioral function in these studies was independent of the duration of dosing. Because duration of dosing had no impact on the kinetics of acrylamide, these data indicate that the toxicity of acrylamide is not due to an accumulation of acrylamide in the target tissue. The less than strict cumulative toxicity of acrylamide may result from an interaction between administered dose, tissue damage, and repair processes.

Acrylamide↗

PubMed1996

Validity of a velodrome test for competitive road cyclists.

The aim of this study was to evaluate the validity of a velodrome field test consisting of repeated rides of 2,280 m, with an initial speed of 28 km.h-1 and increments of 1.5 km.h-1 interspersed with 1-min recovery periods until exhaustion. A group of 12 male competitive road cyclists performed maximal cycling tests under velodrome and laboratory conditions. Velodrome oxygen uptake (VO2) and power output were estimated using equations previously published. Physiological responses to the two tests were compared. Relationships between performance in the velodrome and physiological parameters measured in the laboratory were studied. Maximal power output, heart rate and VO2 were similar in the velodrome and the laboratory [372 (SD 50) vs 365 (SD 36) W, 195 (SD 8) vs 196 (SD 9) beats.min-1 and 4.49 (SD 0.56) vs 4.49 (SD 0.46) l.min-1, respectively], while maximal velodrome blood lactate concentration was significantly higher [13.5 (SD 2.1) vs 11.8 (SD 3.1) mmol.l-1]. Velodrome heart rate was higher at submaximal exercise intensities representing 40%, 50% and 60% of maximal aerobic power, and velodrome blood lactate concentration was also higher at 60%, 70% and 80% of maximal aerobic power. The laboratory parameter that showed the highest correlation with the maximal cycling speed in the velodrome was maximal oxygen uptake (VO2max) expressed per unit of body mass (r = 0.93). In addition, the accuracy of different methods of estimation of the metabolic cost of cycling, rolling resistance, air resistance coefficients and VO2max were compared. Significant differences were found. In conclusion, the present results indicated the validity of a velodrome test used to estimate maximal aerobic parameters of competitive road cyclists, as long as the estimation is made using established equations. When road cyclists are tested in the laboratory, physiological values should be expressed per unit of body surface area or body mass, to predict more accurately the cyclist's performance level under specific field conditions.

Adult↗

PubMed1996

Hormonal responses to training and its tapering off in competitive swimmers: relationships with performance.

During a winter training season, the effects of 12 weeks of intense training and 4 weeks of tapering off (taper) on plasma hormone concentrations and competition performance were investigated in a group of highly trained swimmers (n = 8). Blood samples were collected and the swimmers performed their speciality in competition at weeks 10 (mid-season), 22 (pre-taper) and 26 (post-taper). No statistically significant changes were observed in the concentrations of total testosterone (TT), non-sex hormone binding globulin-bound-testosterone (NSBT), cortisol (C), luteinising hormone, thyroid stimulating hormone, triiodothyronine, thyroxine plasma catecholamines, creatine kinase and ammonia during training and taper. Mid-season NSBT: C ratio and the amount of training were statistically related (r = 0.82, P < 0.05). Competition performance slightly declined during intense training [0.52 (SD 2.51)%, NS] and improved during taper [2.32 (SD 1.69)%, P < 0.01]. Changes in performance during training and taper correlated with changes in ratios TT: C (r = 0.86, P < 0.01 and r = 0.81, P < 0.05, respectively) and NSBT: C (r = 0.77, P < 0.05 and r = 0.76, P < 0.05, respectively). In summary, these results showed that the monitored plasma hormones and metabolic indices were unaltered by 12 weeks of intense training and 4 weeks of taper. The TT: C and NSBT: C ratios, however, appeared to be effective markers of the swimmers' performance capacities throughout the training season.

Adult↗

PubMed1996

Validation of the use of 6,6'-dithiodinicotinic acid as a chromogen in the Ellman method for cholinesterase determinations.

The Ellman method for cholinesterase determination is a spectrophotometric method which entails the use of 5,5'-dithiobis-(2-nitrobenzoic) acid (DTNB) as a chromogen and records the level of cholinesterase activity as the change in absorbance at 412 nm. Although this procedure commonly poses no problem, an exception arises when analyzing tissues rich in hemoglobin, because hemoglobin also optimally absorbs light at 400-430 nm. Use of 6,6'-dithiodinicotinic acid (DTNA) might be a solution because, like DTNB, it also is a chromogen for sulfhydryl groups, but with an optimal absorption wavelength of 340 nm (ie removed from the hemoglobin absorbance maximum). Our validation studies indicate that although DTNA is a slightly less efficient indicator of sulfhydryl group concentration, DTNA yields similar activity and degree of enzyme inhibition in tissues from control and treated animals. Moreover, because the assay is read at 340 nm instead of 412 nm, the DTNA assay is markedly more sensitive for determining cholinesterase activity in hemoglobin-rich tissues. Since the advantages of the DTNA method far outweigh the disadvantages, it should be regarded as a sensitive and convenient procedure for determining cholinesterase activity, especially in hemoglobin-rich tissues.

Absorption↗

PubMed1995

Regulatory and research issues related to cholinesterase inhibition.

Assessing the neurotoxic potential of organophosphate and carbamate pesticides should be greatly facilitated by the knowledge that the mechanism of action of these insecticides is presumed to be the inhibition of cholinesterase, the enzyme which controls the levels of neurotransmitter, acetycholine. Although the inhibition of cholinesterase activity is the recognized mechanism of action, many questions remain regarding the use of cholinesterase inhibition data as a critical effect for establishing risk of cholinesterase-inhibiting pesticides. Specifically, questions have arisen regarding whether blood cholinesterase inhibition correlates with inhibition in target tissues (e.g. brain or muscle) and whether cholinesterase inhibition in any tissue correlates with the adverse clinical and behavioral effects produced by exposure to cholinesterase-inhibiting pesticides. Studies in our laboratory indicate that blood cholinesterase inhibition in both acute and subchronic dosing regimens correlates with inhibition in other tissues, if measurements are taken at the appropriate times. Moreover, there is evidence in the literature and from our laboratory that cholinesterase inhibition correlates with the emergence and severity of clinical signs of poisoning by cholinesterase-inhibiting pesticides.

Animals↗

PubMed1995

Slow accumulation of acetylcholinesterase in rat brain during enzyme inhibition by repeated dosing with chlorpyrifos.

When given to rats, O,O'-diethyl-O-[3,5,6-trichloro-2-pyridyl]- phosphorothionate (chlorpyrifos), a common insecticide, causes an unusually lengthy dose-dependent fall in the activity of brain acetylcholinesterase (AChE; EC 3.1.1.7). To determine whether the slow recovery involves impaired AChE synthesis, experiments were designed to measure AChE activity, immunoreactive AChE protein (AChE-IR) and AChE mRNA. Male, Long-Evans rats, maintained at 350 +/- 5 g, were dosed (s.c.) weekly for 4 weeks with 0, 15, 30, or 60 mg/kg chlorpyrifos in peanut oil. Brain tissue was harvested 1, 3, 5, 7 and 9 weeks after treatment began. AChE activity was measured by Ellman assay, and AChE-IR was estimated by two-site ELISA using monoclonal antibodies to rat brain AChE. While AChE activity fell significantly at all times and doses, AChE-IR increased at 3 and 5 weeks in the two higher dosage groups. Larger increases of AChE-IR were observed after chlorpyrifos was administered for 4 weeks by the oral route. Northern blots quantified with reference to cyclophilin were consistent with stable levels of AChE mRNA. Overall, it appears that chronically reduced brain AChE activity after chlorpyrifos reflects sustained enzyme inhibition, not loss of enzyme protein or suppression of AChE message.

Acetylcholinesterase↗

PubMed1995

Comparison of the relative inhibition of acetylcholinesterase and neuropathy target esterase in rats and hens given cholinesterase inhibitors.

Inhibition of neuropathy target esterase (NTE, neurotoxic esterase) and acetylcholinesterase (AChE) activities was compared in brain and spinal cords of adult While Leghorn hens and adult male Long Evan rats 4-48 hr after administration of triortho-tolyl phosphate (TOTP po, 50-500 mg/kg to hens; 300-1000 mg/kg to rats), phenyl saligenin phosphate (PSP im 0.1-2.5 mg/kg to hens; 5-24 mg/kg to rats), mipafox (3-30 mg/kg ip to hens and rats), diisopropyl phosphorofluoridate (DFP sc, 0.25-1.0 mg/kg to hens; 1-3 mg/kg to rats), dichlorvos (5-60 mg/kg ip to hens; 600-2000 mg/kg to rats), and carbaryl (300-560 mg/kg ip to hens; 30-170 mg/kg to rats). Inhibitions of NTE and AChE were dose-related after administration of all compounds to both species. Hens and rats given TOTP, PSP, mipafox, and DFP demonstrated delayed neuropathy 3 weeks later, with spinal cord lesions and clinical signs more notable in hens. Ratios of NTE/AChE inhibition in hen spinal cord, averaged over the doses used, were 2.6 after TOTP, 5.2 after PSP, 1.3 after mipafox, and 0.9 after DFP, which contrast with 0.53 after dichlorvos, 1.0 after malathion, and 0.46 after carbaryl. Rat NTE/AChE inhibition ratios were 0.9 after TOTP, 2.6 after PSP, 1.0 after mipafox, 0.62 after DFP, 1.3 after dichlorvos, 2.2 after malathion, and 1.1 after carbaryl. The lower NTE/AChE ratios in rats given dosages of the four organophosphorus compounds that caused delayed neuropathy interferred with survival, an effect that was not a problem in hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗

PubMed1995

Association between severity of illness and mortality from nosocomial infection.

BACKGROUND: For the years 1987 through 1992, a study was undertaken to analyze nosocomial infection mortality data and to stratify risk according to severity of underlying illness to compare with published data from the Centers for Disease Control and Prevention. METHODS: Nosocomial infections that contributed to or caused death were identified. In addition, during 1990 through 1992, severity of illness was determined as the subjective estimate of the risk of death or lack of risk of death during the current hospital admission before the onset of the nosocomial infection. These groups were named +SIC and -SIC, respectively. RESULTS: It was determined that the data from death certificates in cases of known nosocomial infection were not sufficient to determine whether nosocomial infection contributed to or caused death. There was a 24% increase in cases of nosocomial infection contributing to or causing death when a physician reviewed deaths in patients with nosocomial infections who did not have a diagnosis of nosocomial infection listed on the death certificate. The rates for nosocomial infections contributing to or causing death are as follows: nosocomial pneumonia, 20%; and bloodstream infections, 19%. In patients who died and had severity of illness determination, there was a statistically significant difference in the rates of nosocomial infections contributing to or causing death between -SIC and +SIC groups for both nosocomial pneumonia and bloodstream infections. The rates for bloodstream infections were as follows: -SIC, 5%; and +SIC, 21%. For nosocomial pneumonia, the rates were as follows: -SIC, 13%; and +SIC, 23%. CONCLUSION: In published reports from the Centers for Disease Control and Prevention, a rate of 13% is given for nosocomial pneumonia and bloodstream infections contributing to or causing death; however, there is no stratification for severity of illness in these reports. The presence of life-threatening illness before the onset of nosocomial pneumonia or bloodstream infection accounts for most deaths among our patients. For valid comparisons, mortality outcome data for nosocomial infections should be stratified for risk according to severity of underlying illness.

Bacteremia↗

PubMed1995

A Mono-Percoll separation technique improves sperm recovery of normal and male factor specimens when compared with the swim-up technique.

The purpose of this study was to determine the effects of a simplified 80% Mono-Percoll sperm separation procedure on both normal and male factor semen samples compared with the standard swim-up technique. The parameters examined include sperm concentration, motility and morphology, total motile functional spermatozoa and percentage recovery. Normal patients demonstrated enhanced sperm parameters with the Mono-Percoll compared with the swim-up technique for concentration (67 x 10(6) versus 42 x 10(6)/ml, P < 0.001), motility (66 versus 59%, P < 0.001), morphology (56 versus 49%, P < 0.005) and percentage recovery (60 versus 42%, P < 0.005). Male factor patients showed enhanced sperm parameters with the Mono-Percoll procedure compared with the swim-up technique for motility (53 versus 42%, P < 0.05) and percentage recovery (54 versus 29%, P < 0.005), with no significant difference in concentration and morphology. In summary, the Mono-Percoll sperm recovery procedure is significantly better than the swim-up technique for male factor patients and patients with normal sperm parameters.

Cell Separation↗

PubMed1994

Studies on the correlation between blood cholinesterase inhibition and 'target tissue' inhibition in pesticide-treated rats.

Inhibition of cholinesterase activity in the blood has been proposed as an index of ChE activity in tissues targeted by ChE-inhibiting pesticides, including the muscle end-plate region and the central nervous system (CNS). While opinions vary regarding the utility of blood ChE activity in predicting ChE activity in the target tissues, there appear to be no comprehensive studies designed to assess this possible correlation in a time- and dose-dependent manner. We undertook this type of study by administering a single dose of an organophosphate, chlorpyrifos (0, 30, 60 or 125 mg/kg in corn oil, s.c.) to rats and then sacrificing animals at 1, 4, 7, 21 or 35 days after dosing. Whole blood, plasma, erythrocytes, frontal cortex, hippocampus, striatum, hypothalamus and diaphragm tissue were collected and assayed for ChE activity. Collapsed across dosages, optimal correlations of blood ChE activity with brain or muscle activity occurred 7-21 days after dosing (when ChE inhibition was maximal and most stable). At all times after dosing, there was a high correlation among ChE activity in the hippocampus, striatum and frontal cortex. Generally, ChE activity in whole blood and erythrocytes correlated better with the activity in brain and muscle than did activity in the plasma (whole blood > or = erythrocytes >> plasma). Similar relationships were also observed in a more abbreviated study using a direct acting organophosphate, paraoxon. ChE activity was determined in blood components, brain and muscle at the time of maximal inhibition (4 h after injection) and during recovery (24 hrs after injection) using two dosage levels (0.17 or 0.34 mg/kg, s.c.). Taken together, these data indicate that the level of ChE activity in the blood may accurately reflect activity in other tissues, but that this correlation is tissue- and time-specific.

Animals↗

PubMed1994

Fenthion produces a persistent decrease in muscarinic receptor function in the adult rat retina.

Several reports have suggested that exposure to organophosphate pesticides damages the visual system. The prolonged effects of an acute dose of fenthion (dimethyl 3-methyl-4-methylthiophenyl phosphorothionate) were studied on the cholinergic system of the rat retina. Fenthion was administered in a single dose of 0 or 100 mg/kg (sc, in corn oil) to adult, male, Long-Evans rats. The animals were killed 4, 14, or 56 days after treatment and cholinesterase (ChE) activity as well as muscarinic receptor (mChR) function measured in the retina and frontal cortex. Fenthion produced 89% inhibition of ChE activity in both tissues at 4 days, and, although there was recovery, slight (15%) inhibition of the enzyme activity was still observed at 56 days in both tissues. A long-lasting decrease in carbachol-stimulated inositolphosphate (IP) release was observed following fenthion treatment in the retina: IP release was depressed at 4 days and this depression persisted up to 56 days after dosing. The density of mChR in the retina as well as in the cortex was decreased by 14-20% at 4 days and returned to control levels by 56 days. Fenthion had no effect on the metabolism of phospholipids in the retina following intraocular injections of labeled precursors [3H]myo-inositol, [methyl-14C]choline, or [2-3H]glycerol 4 days after fenthion treatment. These prolonged effects of fenthion on mChR function (signal transduction) appear to be specific to the retina as the cortex showed no change in receptor-stimulated IP release even in the presence of significant mChR down-regulation and ChE inhibition. This dose of fenthion did not produce overt morphological changes in the retina or in the cortex, as observed with light microscopy, although an increase in glial fibrillary acidic protein immunoreactivity (GFAP IR) extending from the internal limiting membrane to the external limiting membrane of the retina was noted. This increase in GFAP IR was observed at 14 days and persisted as long as 56 days post-treatment in the retina, but was not noted in the cortex at any of the time points studied. Thus, this long-lasting perturbation in the retinal cholinergic second messenger system induced by fenthion may occur independently of depressed ChE activity and down-regulation of mChR.

Animals↗

PubMed1993

Determination of acrylamide in rat serum and sciatic nerve by gas chromatography-electron-capture detection.

A modified method for the derivatization and determination of acrylamide as 2-bromopropenamide by gas chromatography-electron-capture detection was developed and applied to serum and sciatic nerve from rats. The method was accurate and precise over the calibration range 2.24-7.47 micrograms/ml in serum diluted 1:125 and 4-122 micrograms/g in sciatic nerve homogenate (5 mg/ml). limits of detection were estimated to be 1200 ng/ml in undiluted serum and 3 micrograms/g in intact sciatic nerve. The use of less dilute samples to allow for lower limits of detection appears feasible. The time-course of acrylamide in serum and sciatic nerve was studied after acute dosing and indicated elimination half-lives of 1.8 and 2.0 h for serum and sciatic nerve, respectively. A dose-effect relationship was established for each matrix after acute dosing and the measured acrylamide concentrations in serum (microgram/ml) were approximately the same as in sciatic nerve (microgram/g).

Acrylamide↗

PubMed1993

A modified spectrophotometric method appropriate for measuring cholinesterase activity in tissue from carbaryl-treated animals.

Inhibited cholinesterase in tissues of animals exposed to carbamate pesticides is known to reactivate readily, presenting considerable problems in the accurate assessment of cholinesterase activity in these tissues. Decarbamylation of cholinesterase is favored when the tissue samples are diluted and/or are incubated for an extended time. The present study was performed to identify modifications of the commonly used spectrophotometric assay for cholinesterase activity that would minimize spontaneous reactivation of enzyme activity. Those modifications included preincubation of concentrated tissue with concentrated chromogen (i.e., DTNB), dilution to final reaction volume immediately before measurement, and measurement of cholinesterase over a short period of time (5-10 min). The Ellman assay with and without modifications was performed using a microtiter plate reader on tissues from carbaryl-treated rats:undiluted plasma, diluted erythrocytes (1:25), minimally diluted erythrocytes (1:2), diluted brain (1:100), or minimally diluted brain (1:2). The results were compared to cholinesterase activities obtained using a radiometric method which employs minimally diluted tissue and short incubation times. The degree of cholinesterase inhibition for undiluted or minimally diluted tissue assayed by the modified method agreed with those obtained using the radiometric method. Even if the tissues were diluted immediately before assay, however, significant reactivation occurred by the time the first measurements were made by the conventional method. Furthermore, significant spontaneous reactivation may still occur using the modified method if the assay is run for more than 10 min. Use of this modified Ellman method will enable more accurate estimation of in vivo cholinesterase activity in animals treated with carbamates.

Animals↗

PubMed1993

The role of neurotoxic esterase (NTE) in the prevention and potentiation of organophosphorus-induced delayed neurotoxicity (OPIDN).

The first step in the initiation of organophosphorus-induced delayed neuropathy (OPIDN) is proposed to be the phosphorylation of an enzyme found in the nervous system called neurotoxic esterase (neuropathy target esterase, NTE). It has been known for over twenty years that non-neuropathic inhibitors of NTE exist and can actually prevent OPIDN when given before a neuropathic organophosphate (OP). Within the last three years it has become evident that another outcome is possible following in vivo interaction between neuropathic and nonneuropathic NTE inhibitors. When administered after OP exposure, nonneuropathic inhibitors can intensify or potentiate signs of OPIDN in adult chickens. Additionally, whereas developing chickens are typically resistant to the effects of neuropathic OPs, resistant age groups will develop OPIDN when exposure to a neuropathic OP is followed by the non-neuropathic NTE inhibitor phenylmethylsulfonyl fluoride. As in the case of prevention, studies of the potentiation of OPIDN may yield insight into mechanisms involved in the pathogenesis of delayed neurotoxicity. A brief review of current knowledge regarding the role of NTE in both the prevention and potentiation of OPIDN is presented.

Animals↗