Gestational exposure to chlorpyrifos: apparent protection of the fetus?

Previous studies have shown that, in general, young, postnatal animals are more sensitive than adults to the toxic effects of anticholinesterase (antiChE) pesticides. Paradoxically, often fetal brain cholinesterase (ChE) is less inhibited than maternal brain after gestational exposure to an antiChE, presumably due to placental and fetal detoxification of the antiChE. The present investigation was designed to study selected toxicokinetic and toxicodynamic factors surrounding the toxicity of chlorpyrifos (CPF; [O,O'-diethyl O-3,5,6-trichloro-2-pyridyl] phosphorothionate) in pregnant rats dosed repeatedly or singly during late gestation. Dams were dosed daily (po) with CPF in corn oil (0 or 7 mg/kg) on gestational days (GD) 14 to 18. Animals were euthanized at 2 to 120 h after the last dose and tissues were collected for enzyme analysis. Using this dosing regimen, we found that (1) the time of maximal ChE inhibition was the same (i.e., 5-10 h after dosing) for both maternal and fetal brain, (2) the degree of fetal brain ChE inhibition was 4.7 times less than maternal brain inhibition, and (3) the detoxification potential (i.e., carboxylesterase and chlorpyrifos-oxonase) of the fetal tissues was very low compared to the maternal tissues. A separate group of experiments showed that if pregnant dams received only one oral dose of 7 or 10 mg/kg CPF on GD18, the degree of ChE inhibition in the fetal brain was comparable to the maternal brain ChE inhibition. Taking into consideration the net increase (more than fourfold) in fetal brain ChE activity from GD14 to 18 in control animals, and the fact that maternal brain ChE was inhibited more than fetal brain ChE only in a repeated-dosing regimen, we conclude that the fetus is not genuinely protected from the toxic effects of a given dose of CPF. We propose that fetal brain ChE is simply able to recover more fully between each dose as compared to maternal brain ChE, giving the illusion that the fetal compartment is less affected than the maternal compartment.

Hematological responses to training and taper in competitive swimmers: relationships with performance

The purpose of this study was to monitor hematological changes during 12 weeks of intense training and 4 weeks of taper in 8 highly trained competitive swimmers, and to assess the relationships between hematological variables and competition performance. Venous blood samples were obtained in the mid-season (wk 10), before taper (wk 22) and after taper (wk 26). Swimmers participated in actual competitions within 1 wk of each blood testing. Comparisons were made between swimmers improving performance with taper by more than 2% (n = 4), efficient (GE) or less than 2% (n = 4), less efficient (GLE). Hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) increased significantly during training. MCH and MCHC decreased during taper, while serum iron tended to increase (P = 0.07). Improvement in performance during taper was positively correlated with post-taper red cell count (RCC): r = 0.83, P < 0.05. GE swimmers had higher pre- and post-taper RCC, and post-taper Hb and hematocrit. In conclusion, intense training and taper appeared to influence the hematological status and performance capacity of the studied group of swimmers.

Age- and gender-related differences in the time course of behavioral and biochemical effects produced by oral chlorpyrifos in rats

It is well known that young animals are generally more sensitive to lethal effects of cholinesterase-inhibiting pesticides, but there are sparse data comparing less-than-lethal effects. We compared the behavioral and biochemical toxicity of chlorpyrifos in young (postnatal Day 17; PND17) and adult (about 70 days old) rats. First, we established that the magnitude of the age-related differences decreased as the rat matures. Next, we evaluated the time course of a single oral dose of chlorpyrifos in adult and PND17 male and female rats. Behavioral changes were assessed using a functional observational battery (with age-appropriate modifications for pre-weanling rats) and an evaluation of motor activity. Cholinesterase (ChE) activity was measured in brain and peripheral tissues and muscarinic receptor binding assays were conducted on selected tissues. Rats received either vehicle (corn oil) or chlorpyrifos (adult dose: 80 mg/kg; PND17 dose: 15 mg/kg); these doses were equally effective in inhibiting ChE. The rats were tested, and tissues were then taken at 1, 2, 3.5, 6.5, 24, 72, 168, or 336 h after dosing. In adult rats, peak behavioral changes and ChE inhibition occurred in males at 3.5 h after dosing, while in females the onset of functional changes was sooner, the time course was more protracted and recovery was slower. In PND17 rats, maximal behavioral effects and ChE inhibition occurred at 6.5 h after dosing, and there were no gender-related differences. Behavioral changes showed partial to full recovery at 24 to 72 h, whereas ChE inhibition recovered markedly slower. Blood and brain ChE activity in young rats had nearly recovered by 1 week after dosing, whereas brain ChE in adults had not recovered at 2 weeks. Muscarinic-receptor binding assays revealed apparent down-regulation in some brain areas, mostly at 24 and 72 h. PND17 rats generally showed more receptor down-regulation than adults, whereas only adult female rats showed receptor changes in striatal tissue that persisted for 2 weeks. Thus, compared to adults (1) PND17 rats show similar behavioral changes and ChE inhibition although at a five-fold lower dose; (2) the onset of maximal effects is somewhat delayed in the young rats; (3) ChE activity tended to recover more quickly in the young rats; (4) young rats appear to have more extensive muscarinic receptor down-regulation, and (5) young rats show no gender-related differences.

Rat brain acetylcholinesterase activity: developmental profile and maturational sensitivity to carbamate and organophosphorus inhibitors

A growing body of evidence indicates that young animals exhibit an increased susceptibility to the lethal effects of cholinesterase (ChE)-inhibiting insecticides. Our laboratory is engaged in defining factors which may explain this age-related sensitivity. This report includes results from experiments designed to compare the developmental profiles, kinetic parameters and intrinsic (i.e. in vitro) sensitivity of developing male rat brain acetylcholinesterase (AChE) activity to carbamate and organophosphorus anticholinesterases. Total ChE activity in whole brain for each age was composed of about 90% AChE and 10% butyrylcholinesterase (BuChE) activity for the six ages examined. Brain AChE activity showed an age-related increase in Vmax until postnatal day 17 with no change in Km (average of all six ages approximately equal to 72 microM). Optimal substrate (acetylthiocholine) concentration for each age was 1 mM, and there was substrate inhibition (approximately 10%) at 2.5 mM. IC50s (the concentration of compound that inhibits 50% of the AChE activity in 30 min at 26 degrees C) defined concomitantly for postnatal day 4 and adult brain AChE using either aldicarb, carbaryl, chlorpyrifos-oxon or malaoxon were virtually identical at both ages with average IC50 values being: aldicarb = 2.4 microM, carbaryl = 1.7 microM, chlorpyrifos-oxon = 4.9 nM and malaoxon = 140 nM. In summary, AChE in young and adult brain differs mostly in specific activity while the Km(s), substrate profiles, and in vitro sensitivity to selected anticholinesterase insecticides are not different. Therefore, these data support the hypothesis that the greater sensitivity of the young animals to anticholinesterase pesticides is not due to the greater sensitivity of the target molecule AChE to these inhibitors.

Ontogenetic differences in the regional and cellular acetylcholinesterase and butyrylcholinesterase activity in the rat brain

Considering the novel functions for both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the developing nervous system (reviewed in Layer and Willbold, Prog. Histochem. Cytochem., 1995) a quantitative survey of the spatiotemporal developmental profiles of both AChE and BuChE activity in the neonatal rat brain would be extremely useful. To that end, we collected six brain regions at seven developmental time points, (postnatal day 1, 4, 7, 12, 17, 21, adult; n > or = 3) and measured AChE and BuChE activity using both biochemical and histological methods. These results indicated that the developmental pattern of AChE and BuChE activity varied with respect to brain region and age: (1) the ontogeny of either AChE or BuChE specific activity in one region was not necessarily indicative of the developmental pattern of the same cholinesterase in other regions; (2) the AChE developmental profile in a given region did not necessarily predict the BuChE developmental pattern for that same region. The data were also analyzed from a different perspective, i.e., the ratio of BuChE-AChE activity, in order to determine if BuChE activity preceded AChE activity during development as has been proposed for the chick nervous system (Layer, Proc. Natl. Acad. Sci. USA, 1983). Our analysis showed that, in general, the BuChE-AChE ratio decreased as the region matured, data which parallel the pattern of development of these esterases in the chick nervous system.

Common mechanism of toxicity: a case study of organophosphorus pesticides

The Food Quality Protection Act of 1996 (FQPA) requires the EPA to consider "available information concerning the cumulative effects of such residues and other substances that have a common mechanism of toxicity ... in establishing, modifying, leaving in effect, or revoking a tolerance for a pesticide chemical residue." This directive raises a number of scientific questions to be answered before the FQPA can be implemented. Among these questions is: What constitutes a common mechanism of toxicity? The ILSI Risk Science Institute (RSI) convened a group of experts to examine this and other scientific questions using the organophosphorus (OP) pesticides as the case study. OP pesticides share some characteristics attributed to compounds that act by a common mechanism, but produce a variety of clinical signs of toxicity not identical for all OP pesticides. The Working Group generated a testable hypothesis, anticholinesterase OP pesticides act by a common mechanism of toxicity, and generated alternative hypotheses that, if true, would cause rejection of the initial hypothesis and provide criteria for subgrouping OP compounds. Some of the alternative hypotheses were rejected outright and the rest were not supported by adequate data. The Working Group concluded that OP pesticides act by a common mechanism of toxicity if they inhibit acetylcholinesterase by phosphorylation and elicit any spectrum of cholinergic effects. An approach similar to that developed for OP pesticides could be used to determine if other classes or groups of pesticides that share structural and toxicological characteristics act by a common mechanism of toxicity or by distinct mechanisms.

Comparison of the in vitro sensitivity of rat acetylcholinesterase to chlorpyrifos-oxon: what do tissue IC50 values represent?

The toxicological literature is replete with studies which have attempted to correlate differences in in vivo sensitivity to anticholinesterases with a common in vitro measure: acetylcholinesterase (AChE) IC50 values. Generally, it is assumed that these IC50 values reflect the intrinsic sensitivity of the AChE molecule to the inhibitor. Our goal was to ascertain whether differences in AChe sensitivity to an organophosphate (i.e., IC50 values) are due to varying properties of the enzyme molecule (i.e., present assumption) or to extrinsic factors. Tissue samples were obtained from immature and adult Long-Evans rats. AChE IC50 values were determined by incubating tissue homogenates with chlorpyrifos-oxon (active metabolite of chlorpyrifos, a common organophosphate insecticide) for 30 min at 26 degrees C, and then measuring residual AChE activity. The following IC50 values were noted for postnatal day 4 and adult animals, respectively: brain, 10 nM for both ages; liver, 96 and 527 nM; plasma, 18 and 326 nm. Thus, the "apparent" sensitivity of AChe was prone to vary dramatically with age and tissue type. In contrast, when AChE was isolated from the same tissues by immunoprecipitation, there were no age- or tissue- related differences (IC50 approximately equal to 3 nM in every case). These data show clearly that IC50 values from a crude homogenate do not measure the true sensitivity of AChE to the inhibitor. Presumably, for chlorpyrifos-oxon, at least, the tissue IC50 values depend greatly on a tissue's propensity to sequester or hydrolyze chlorpyrifos-oxon.

Creatine supplementation as an ergogenic aid for sports performance in highly trained athletes: a critical review

Creatine supplementation has become a common practice among competition athletes participating in different sports over the last few years. The mechanism by which supplementary creatine could have potential ergogenic effects would be an increased muscle creatine and phosphocreatine concentration, leading to a higher rate of ATP resynthesis, a delay in the onset of muscular fatigue and a facilitated recovery during repeated bouts of high-intensity exercise. A critical review of the literature reveals that these ergogenic effects, when found, have been generally shown in untrained subjects performing several exercise bouts under laboratory conditions. The limited body of scientific data available concerning highly trained athletes performing single competition-like exercise tasks indicates that this type of population does not benefit from creatine supplementation. Therefore, the widespread use of creatine ingestion to improve competition performance does not seem to be justified. The potential interest of creatine supplementation for elite athletes could be related to an increased ability to perform repeated high-intensity exercise bouts, either during training or during competition in sports in which repeated efforts are required (e.g. soccer, basketball), but this possibility needs scientific confirmation.

The relationship of oral chlorpyrifos effects on behavior, cholinesterase inhibition, and muscarinic receptor density in rat

Behavioral changes and tissue cholinesterase (ChE) inhibition were examined in animals treated with the commonly used insecticide chlorpyrifos. Adult male rats were dosed by gavage with 0, 10, 30, 60, or 100 mg/kg chlorpyrifos. Rats (n = 20/dose group) were evaluated using a functional observational battery (FOB) and an automated measure of motor activity. All rats were tested the day before dosing and at 3.5 h (the time of peak effect) after dosing; half of these (n = 10/dose) were sacrificed immediately after testing for tissue collection. The remaining rats were tested again at 24 h, followed by sacrifice. The following tissues were collected from each animal: half brain, individual brain areas from the other half of the brain (frontal cortex, hippocampus, striatum, hypothalamus, cerebellum, pons/medulla), retina, liver, heart, diaphragm, quadriceps femoris muscle, and blood (separated into whole blood, plasma, and erythrocytes). ChE activity was measured in all tissues, and muscarinic receptor density was assessed as quinuclidinyl benzilate (QNB) binding in all brain regions, heart, and retina. The lowest dose produced no behavioral effects but did produce significant ChE inhibition in most tissues at 3.5 h. Higher doses produced more ChE inhibition and cholinergic signs of toxicity. Partial recovery from behavioral effects was evident at 24 h, with little or no corresponding recovery of ChE activity. Apparent downregulation of muscarinic receptor density was noted only in striatum and pons/medulla of rats treated with the highest dose of chlorpyrifos. Correlations for behavioral and biochemical effects were generally poor because: a) the low-dose effects on ChE inhibition were not reflected in behavioral signs, and b) behavioral signs showed recovery at 24 h, whereas ChE activity did not. Examination of data for individual rats indicated that > 60% of brain ChE inhibition was reached before neurobehavioral effects were evident.

Tissue-specific effects of chlorpyrifos on carboxylesterase and cholinesterase activity in adult rats: an in vitro and in vivo comparison

Organophosphate (OP) pesticides can bind to carboxylesterase (CaE), which may lower the concentration of OPs at the target site enzyme, acetylcholinesterase (ChE). It is unclear from the literature whether it is the CaE's affinity for the OP and/or the number of CaE molecules which is the dominant factor in determining the protective potential of CaE. We undertook a detailed, in vitro and in vivo survey of both CaE and ChE to ascertain if in vitro sensitivity of CaE and ChE predicted the pattern of inhibition seen after in vivo dosing with chlorpyrifos (CPF; 80 mg/kg, p.o.) in male or female adult Long-Evans rats. For the brain, the in vitro sensitivity to CPF-oxon did predict the in vivo patterns of inhibition: In vitro, brain ChE was approximately 25 times more sensitive to the active metabolite, CPF-oxon, than brain CaE, and in vivo brain ChE was more inhibited than brain CaE. In contrast, the in vitro sensitivity of plasma ChE and CaE did not correlate well with the in vivo pattern of inhibition: In vitro, plasma ChE was approximately 6.5 times less sensitive to CPF-oxon than plasma CaE, but in vivo, plasma ChE was more inhibited than CaE. In order to understand the role of CaE in protecting the brain ChE from inhibition by CPF-oxon in vitro, adult rat striatal tissue was incubated in the presence and absence of adult rat liver tissue and IC50s of CPF-oxon were determined. The increase in the striatal CPF-oxon IC50 value noted for ChE in the presence of liver suggested that CaE was binding the CPF-oxon and limiting its access to ChE. Male liver CaE, which has the same affinity for binding CPF-oxon as female liver CaE but has twice as many binding sites, caused a greater increase in the striatal CPF-oxon IC50 than female liver, suggesting that the number of binding sites does play a role in the detoxification potential of a tissue. In summary, we found that (1) there are tissue and gender-related differences for basal ChE and CaE activity; (2) the in vitro sensitivity of CaE or ChE to CPF-oxon is highly tissue-specific; (3) the pattern of ChE and CaE inhibition after in vivo dosing with CPF is not necessarily predictable from the in vitro IC50 for these same enzymes, and (4) the number of CaE molecules may play a role in modifying the toxicity of CPF.

Cellular mechanisms for developmental toxicity of chlorpyrifos: targeting the adenylyl cyclase signaling cascade

Developmental neurotoxicity caused by chlorpyrifos exposure is generally thought to target cholinesterase but chlorpyrifos may also act on cellular intermediates, such as adenylyl cyclase, that serve global functions in the coordination of cell development. In the current study, neonatal rats were exposed to apparently subtoxic doses of chlorpyrifos (no weight loss, no mortality) either on Postnatal Days 1-4 or on Postnatal Days 11-14, and the effects on components of the adenylyl cyclase cascade were evaluated in brain regions that are enriched (forebrain) or sparse (cerebellum) in cholinergic innervation, as well as in a nonneural tissue (heart). In all three, chlorpyrifos evoked deficits in multiple components of the adenylyl cyclase cascade: expression and activity of adenylyl cyclase itself, functioning of G-proteins that link neurotransmitter and hormone receptors to cyclase activity, and expression of neurotransmitter receptors that act through this cascade. Disruption of signaling function was not restricted to transduction of cholinergic signals but rather extended to adrenergic signals as well. In most cases, the adverse effects were not evident during the immediate period of chlorpyrifos administration, but appeared after a delay of several days. These results suggest that chlorpyrifos can affect cell development by altering the activity and reactivity of the adenylyl cyclase signaling cascade, a major control point for trophic regulation of cell differentiation. The effects are not restricted to cholinergic targets, nor even to the central nervous system. Hence, disruption of cell development by chlorpyrifos is likely to be more widespread than previously thought.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.