Cross validation of multiple methods for measuring pyrethroid and pyrethrum insecticide metabolites in human urine

The objective of our study was to compare three vastly different analytical methods for measuring urinary metabolites of pyrethroid and pyrethrum insecticides to determine whether they could produce comparable data and to determine if similar analytical characteristics of the methods could be obtained by a secondary laboratory. This study was conducted as a part of a series of validation studies undertaken by the German Research Foundation's Committee on the Standardization of Analytical Methods for Occupational and Environmental Medicine. We compared methods using different sample preparation methods (liquid-liquid extraction and solid-phase extraction with and without chemical derivatization) and different analytical detection methods (gas chromatography-mass spectrometry (single quadrupole), gas chromatography-high resolution mass spectrometry (magnetic sector) in both electron impact ionization and negative chemical ionization modes, and high-performance liquid chromatography-tandem mass spectrometry (triple quadrupole) with electrospray ionization). Our cross validation proved that similar analytical characteristics could be obtained with any combination of sample preparation/analytical detection method and that all methods produced comparable analytical results on unknown urine samples.

Bistability with hysteresis in the activity of vasopressin cells

Magnocellular vasopressin neurones generate distinctive 'phasic' patterns of electrical activity during which periods of spiking activity (bursts) alternate with periods of no spikes or occasional spikes. The mechanisms of burst termination in vivo are still not clearly understood. We recorded from single phasic vasopressin cells in vivo and here we show that burst terminations in some phasic cells is preceded by transient increases in activity, consistent with bursts ending as a result of activity-dependent inhibition. We show that extrinsically imposed increases in activity, evoked by brief stimulation of the organum vasculosum of the lamina terminalis, can either trigger bursts if given when a cell is silent, or stop bursts if given when a cell is active. Thus, the magnocellular vasopressin system is a population of independent bistable oscillators. The population as a whole is insensitive to transient changes in input level, whether these are excitatory or inhibitory. The vasopressin cell population thus acts like a 'low-pass filter'; although brief large changes in input rate have little overall effect, the population responds very effectively to small, sustained changes in input rate by evolving a pattern of discharge activity that efficiently maintains secretion. We note that these filtering characteristics are the opposite of the filtering characteristics that are typically associated with neurones.

Effects of alpha-melanocyte-stimulating hormone on magnocellular oxytocin neurones and their activation at intromission in male rats

The peptides alpha-melanocyte-stimulating hormone (alpha-MSH) and oxytocin have very similar effects on several behaviours, including male sexual behaviour. Both induce penile erection and enhance copulatory behaviour when given centrally, suggesting that their central actions are not independent. Here, we used intromission as a physiological stimulus to investigate whether some central effects of alpha-MSH during male sexual behaviour are mediated by oxytocin neurones. We used the expression of the immediate-early gene product Fos to investigate oxytocin neurone activation at intromission and after intracerebroventricular (i.c.v.) administration of alpha-MSH (1 microg/5 microl) and studied the effects of i.c.v. administration of a MC4 receptor antagonist on Fos expression and on the latency of male rats to exhibit sexual behaviour in the presence of a receptive female. In rats that showed intromission, Fos was expressed in magnocellular oxytocin neurones in both the paraventricular nucleus (PVN) and the supraoptic nucleus (SON), but there was no significant activation of parvocellular oxytocin neurones of the PVN. Similarly, alpha-MSH increased Fos expression in magnocellular oxytocin neurones but had little or no effect in parvocellular oxytocin neurones. In male rats that achieved intromission, central injection of a MC4 receptor antagonist significantly attenuated the increase in Fos expression in magnocellular oxytocin neurones in both the PVN and the SON and increased mount and intromission latencies compared to vehicle-injected controls. Together, the results indicate that magnocellular oxytocin neurones are involved in the central regulation of male sexual behaviour, and that some of the central effects of alpha-MSH are likely to be mediated by magnocellular oxytocin neurones.

Jacques Benoit Lecture. Information processing in the hypothalamus: peptides and analogue computation

Peptides in the hypothalamus are not like conventional neurotransmitters; their release is not particularly associated with synapses, and their long half-lives mean that they can diffuse to distant targets. Peptides can act on their cells of origin to facilitate the development of patterned electrical activity, they can act on their neighbours to bind the collective activity of a neural population into a coherent signalling entity, and the co-ordinated population output can transmit waves of peptide secretion that act as a patterned hormonal analogue signal within the brain. At their distant targets, peptides can re-programme neural networks, by effects on gene expression, synaptogenesis, and by functionally rewiring connections by priming activity-dependent release.

Biomarker of pyrethrum exposure

Pyrethrum as well as synthetic pyrethroids like allethrin, resmethrin, phenothrin, tetramethrin, cyfluthrin, cypermethrin, deltamethrin or permethrin are among the insecticides most often used worldwide. With a sensitive and valid gas-chromatographic-high resolution mass spectrometric method, it is possible to detect all pyrethrum and pyrethroid metabolites in one analytical run. Thus, for the first time a background level of trans-chrysanthemumdicarboxylic acid (CDCA) in urine (95th percentile: 0.15 microg/l) as a characteristic, e.g. for a pyrethrum exposure was found. Following a pyrethrum exposure lasting 1 day, CDCA was found in 27 out of 30 subjects with concentrations going up to 54 microg/l urine (mean: 1.1+/-4.4 microg/l). To obtain information about the elimination kinetics of pyrethrum in humans, urinary excretion of CDCA was investigated in three volunteers after oral intake of 0.3mg pyrethrin I. CDCA was detected during the first 36 h after intake with elimination being most rapid during the first 4h (mean elimination half-life: 4.2h).

Analysis of biomarkers in rats and dogs exposed to polymeric methylenediphenyl diisocyanate (pMDI) and its glutathione adduct

Hemoglobin adducts (Hb-MDX) of monomeric methylenediphenyl diisocyanate (MDI) are often interpreted as indirect evidence of hydrolysis of the diisocyanate moiety to the respective amine (diphenylmethane-4,4'-diamine, 4,4'-MDA) which constitutes the rationale of using this biomarker as an internal dosimeter of exposure to putatively formed MDA. In contrast, more recently published data suggest that following inhalation the high concentration of glutathione (GSH) present in lungs favor an adduct formation with GSH and/or peptides/proteins rather than hydrolysis. The focus of this study was to test this alternate hypothesis, viz. whether Hb-MDX can also be formed by the GSH bis-adduct of monomeric MDI. The synthesized mMDI-GSH bis-adduct was administered to rats by single intratracheal instillation. Additional groups were dosed by gavage and intraperitoneal injection. Biomarkers of exposure were determined in blood (plasma protein and hemoglobin adducts) and urine after harsh alkaline and acid hydrolysis, respectively. Data from previous single inhalation exposure studies with aerosols of MDI and 4,4'-MDA in rats served as reference. As to whether N-acetylation plays any modifying role to yield these mMDI-specific biomarkers was addressed in similarly head-only exposed dogs, a species with no appreciable N-acetylation capacity whereas rats are strong N-acetylators. The results obtained suggest that biomarkers in blood from controlled exposures above current workplace standards of mMDI appear not to be suitable for reliable assessments of past exposures. The biomarkers typically used to assess past exposures to MDI were also identified following exposure to the MDI-GSH bis-adduct. Their yield was low but quite similar for MDI aerosol and the MDI-GSH bis-adduct, whilst that of MDA was distinctively higher. The findings of this study are supportive of a conceptual pathway that the MDI-derived biomarkers of exposure are formed through MDI-GSH adducts rather than MDA. Data from dogs support the findings from rats and show that N-acetylation does not appear to be an essential modifying factor. It is concluded that the yield of MDI-related markers of exposure is relatively low and dependent on the exposure dose (and route). MDA originating from hydrolyzed serum protein or hemoglobin appear to be confounded by false-positive background levels which are surmised to be associated with the method of hydrolysis. The determination of urinary biomarkers might be a useful tool to identify recent exposures (by any route). Due methodological uncertainties associated with the harsh hydrolysis of biological specimens may be reduced substantially when using incremental pre- to post-shift changes rather than relying solely on absolute data.

Modelling the hypothalamic control of growth hormone secretion

Here, we construct a mathematical model of the hypothalamic systems that control the secretion of growth hormone (GH). The work extends a recent model of the pituitary GH system, adding representations of the hypothalamic GH-releasing hormone (GHRH) and somatostatin neurones, each modelled as a single synchronised unit. An unpatterned stochastic input drives the GHRH neurones generating pulses of GHRH release that trigger GH pulses. Delayed feedback from GH results in increased somatostatin release, which inhibits both GH secretion and GHRH release, producing an overall pattern of 3-h pulses of GH secretion that is very similar to the secretory profile observed in male rats. Rather than directly stimulating somatostatin release, GH feedback triggers a priming effect, increasing releasable stores of somatostatin. Varying this priming effect to reduce the effect of GH can reproduce the less pulsatile form of GH release observed in the female rat. The model behaviour is tested by comparison with experimental observations with a range of different experimental protocols involving GHRH injections and somatostatin and GH infusion.

Low pilot exposure to pyrethrin during ultra-low-volume (ULV) aerial insecticide application for control of adult mosquitoes

Pilot exposure to pyrethrin was monitored after 2 aerial applications of a ultra-low-volume (ULV) pyrethrin insecticide for the control of adult mosquitoes. Pyrethrin exposure was estimated by measuring the excretion in urine of a common metabolite, trans-chrysanthemumdicarboxylic acid, of the natural pyrethrin mixture. Pyrethrin exposure estimated by total daily urine volume was well correlated (R2 = 0.8) with exposure estimated by the creatinine-adjusted volume of combined workday urine voids, indicating that a postapplication spot urine sample would be sufficient to measure pyrethrin exposure. Pilot exposure to pyrethrin was very low after both insecticide applications. The highest exposure was found on day 1, with a dose of 2.05 microg pyrethrin equivalents/day or a dosage of 0.03 microg pyrethrin equivalents/kg/day. These exposure rates represent approximately 1/2,800,000th of the low observed adverse effect level and 1/1,000th of the acceptable daily intake for pyrethrin. The aerial application of ULV pyrethrin insecticide for the control of adult mosquitoes does not result in undue exposure to a pilot who is trained and certified to conduct such control operations.

Pyrethroids used indoor - ambient monitoring of pyrethroids following a pest control operation

House dust and airborne particles (PM) were sampled before (T1) and 1 day (T2), 4-6 months (T3) as well as 10-12 months (T4) after a pest control operation (PCO). Cyfluthrin was applied in 11, cypermethrin in 1, deltamethrin in three and permethrin in four interiors. The pyrethroid concentrations in house dust and PM were measured by GC/MS with a detection limit for all pyrethroids of 0.5 mg/kg house dust and of 1 ng/m3 PM for deltamethrin and permethrin and 3 ng/m3 PM for cyfluthrin and cypermethrin. A general background concentration of permethrin (95th percentile: 5.9 mg/kg) and cyfluthrin (95th percentile: 34.9 mg/kg) in house dust was found. In general, an appropriately performed PCO lead to an increase of pyrethroids in house dust as well as in PM, in some cases up to 1 year after application. One day after the application the cyfluthrin concentration increased significantly from 0.25 (T1) to 33.8 mg/kg house dust (T2) and up to 4.9 ng/m3 in PM. The permethrin concentration increased significantly from 4.3 to 70 mg/kg in house dust and up to 18.1 ng/m3 in PM, deltamethrin increased to 54.5 mg/kg and 20.8 ng/m3 and cypermethrin to 14 mg/kg and 45.7 ng/m3. Thereafter a continuous decrease could be observed during the time course of 1 year. After 1 year the permethrin concentration in house dust was still 1/5 of the T2 concentration, whereas for cypermethrin and cyfluthrin only 1/14 and 1/23 of the T2 concentration were found. Deltamethrin was not detected at all after T2. Moreover, the data of this study showed significant, positive correlations between pyrethroids in house dust and in airborne particles especially one day after PCO.

Simultaneous determination of pyrethroid and pyrethrin metabolites in human urine by gas chromatography–high resolution mass spectrometry

A new developed gas chromatographic-high resolution mass spectrometric method for the sensitive simultaneous determination of trans-chrysanthemumdicarboxylic acid, cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid, cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid, 3-phenoxybenzoic acid and 4-fluoro-3-phenoxybenzoic acid in human urine is presented. These metabolites are biomarkers for an exposure to pyrethrum, allethrin, resmethrin, phenothrin, tetramethrin, cyfluthrin, cypermethrin, deltamethrin or permethrin. Therefore, with the help of this method for the first time a complete assessment of exposure to pyrethroid and pyrethrin insecticides is possible. After acid hydrolysis and extraction with tert-butyl-methyl-ether the residue is derivatized with 1,1,1,3,3,3-hexafluoroisopropanol and analyzed by GC/HRMS in electron impact mode (detection limits < 0.1 microg/l) as well as in negative chemical ionization mode (detection limit < 0.05 microg/l urine).

Estimation of parameters for a mathematical model of growth hormone secretion

Here, we describe partial calibration of a parsimonious mathematical model of growth hormone (GH) secretion. From first principles, we derived a model of the effects on GH secretion from pituitary somatotrophs of stimulation by GH-releasing factor (GRF) or GH secretagogue, and of inhibition by somatostatin. We obtained a concise model by collapsing the many processes of the signal transduction cascade into a single step broadly reflecting the initial binding of GRF to its receptors. In the model, GH secretion is proportional to the rate of binding of GRF to activatable receptors. Desensitization occurs because of reduction of free receptors/available effector units, and resensitization occurs as those lost are replaced. This replacement is speeded up in the presence of somatostatin, which also inhibits GH secretion by reducing the constant of proportionality between the rate of GH secretion and the rate of GRF binding. We derived simple mathematical equations for the rate of GH secretion and cumulative secretion. Using these, we tested the model against data obtained from experiments performed in vitro, and made it quantitative using rigorous statistical approaches to optimize parameter estimates. The behaviour of the calibrated model matches experimental observations closely.

A sensitive class specific immunoassay for the detection of pyrethroid metabolites in human urine

The pyrethroids are one of the most heavily used insecticide classes in the world. It is important to develop sensitive and rapid analytical techniques for environmental monitoring and assessment of human exposure to these compounds. Because major pyrethroids contain a phenoxybenzyl group and phenoxybenzoic acid (PBA) is a common metabolite form or intermediate, PBA might be used as a biomarker of human exposure to pyrethroids. A sensitive and selective immunoassay for the common pyrethroid metabolite PBA was developed. Rabbits were immunized with 3-[4-(3-carboxyphenoxy)phenoxy] N-thyroglobulin ethylamine. All sera were screened against numerous coating antigens. The assay with the least interference and the best sensitivity was optimized and characterized. The average IC50 for free PBA was 1.65 ng/mL. No cross-reactivity was measured to parent pyrethroids and other metabolites. Urine matrix effects can be eliminated by simple dilution. Results from urine samples from exposed workers suggest that this PBA immunoassay might be suitable as a monitoring tool for human exposure to pyrethroids.

Effects of neurotensin on the organization of activity in supraoptic nucleus cells in virgin and lactating rats

Neurotensin increases the firing rate of supraoptic nucleus oxytocin and vasopressin neurones in vitro and induces Fos protein expression in the supraoptic nucleus in vivo. Here, we used extracellular single-unit electrophysiological recording combined with local microdialysis administration of neurotensin (1 mM at 2 micro l/min) to investigate the effects of locally applied neurotensin on the firing of oxytocin and vasopressin neurones in urethane-anaesthetized virgin and lactating rats. Neurotensin decreased the mean firing rate of oxytocin cells in virgin, but not lactating, rats. In addition, neurotensin increased the index of dispersion (a measure of the variability of firing) in virgin, but not lactating, rats. By contrast to oxytocin cells, neurotensin increased the mean firing rate of vasopressin cells in both virgin and lactating rats, but did not alter the index of dispersion. The increase in firing of phasic vasopressin cells was achieved through an increase in intraburst frequency (rather than an increase in burst duration or decrease in interburst interval), which resulted from a reduction of the spike-frequency adaptation that develops over the course of phasic bursts. Thus, neurotensin has differential effects on activity patterning in oxytocin and vasopressin cells and the effects on oxytocin cells, but not vasopressin cells, depend upon the physiological status of the animal. The increase in the variability of firing of oxytocin cells induced by neurotensin in virgin rats, but not in lactating rats, suggests that neurotensin (or other neurotransmitters/neuromodulators with similar actions) might establish conditions that predispose oxytocin cells to fire in milk-ejection bursts in lactating rats.

Temporal dissociation of the feedback effects of dendritically co-released peptides on rhythmogenesis in vasopressin cells

Vasopressin neurones fire action potentials in a rhythmic 'phasic' pattern, characterised by alternating periods of activity and silence. Vasopressin and dynorphin are co-packaged in neurosecretory vesicles that are exocytosed from vasopressin cell dendrites and terminals and both have been implicated in the generation of phasic activity patterning through autoregulatory mechanisms. Here, identified supraoptic nucleus vasopressin cells exhibiting spontaneous phasic activity were recorded from urethane-anaesthetised rats administered the V1 vasopressin receptor antagonist, OPC 21268, or the kappa-opioid receptor antagonist, nor-binaltorphimine. OPC 21268 elevated firing rate throughout each burst whereas nor-binaltorphimine excitation emerged over the course of each burst, indicating a progressive activation of kappa-opioid receptor mechanisms during bursts. To determine whether changes in post-spike excitability could account for these effects, we plotted the probability of action potential firing with time after the preceding action potential (hazard function) and found that, similarly to firing rate, this too was elevated by OPC 21268 throughout each burst whilst the excitatory effects of nor-binaltorphimine progressively increased over the course of each burst. Thus, the temporal organisation of the feedback effects of these co-released peptides is different, with vasopressin effectively causing an immediate reduction in overall excitability whilst dynorphin causes a progressive decrease in post-spike excitability over the course of each burst.

Modelling the pituitary response to luteinizing hormone-releasing hormone

The pituitary response to luteinizing hormone-releasing hormone (LHRH) is steroid-dependent and varies throughout the reproductive cycle, but the rapid rise in pituitary sensitivity on the day of the ovulation-inducing LH surge is due to a 'self-priming' effect of exposure to LHRH that results in a potentiation of pituitary responsiveness 35-40 min later. The expression of this effect is itself steroid-dependent, and is most marked on pro-oestrus. Here, a model of LHRH-induced LH release was developed to incorporate the changes in pituitary sensitivity observed throughout the reproductive cycle. LH release is based on the Law of Mass Action, and a component related to self-priming is included in the model, incorporating the delay between initial exposure and potentiation of responsiveness and an upper maximum to the achievable level of priming. Where possible, model parameters were obtained from biological values, otherwise they were optimized to fit an experiment performed in vivo. These parameters were then used to test the model against other experimental data obtained both in vivo and in vitro. The model provided a good fit to the in vivo data but the in vitro experimental data required a change in one parameter, the upper limit of priming. We conclude that this model of the pituitary release mechanism can simulate the changes in pituitary responsiveness throughout the reproductive cycle. We suggest that substitution of this model in a previous model of the LHRH pulse generator could allow more appropriate tests of the LHRH pulse generator model.

Concentration-dependence of biomarkers of exposure of methylenediphenyl-diisocyanate following acute inhalation exposure of rats

Rats were nose-only exposed for 6 h to polymeric methylenediphenyl-diisocyanate (pMDI). Concentrations varied from 0.12 to 12.7 mg/m(3) using a highly respirable aerosol. In regard to the concentration of the monomeric fraction of MDI contained in pMDI, the lowest concentration was in the range of the current workplace limit of MDI which is 0.05 mg/m(3). Biomarkers of exposure were determined in hydrolyzed urine (collection started after cessation of exposure for approximately 18 h; acid hydrolysis) and hydrolyzed hemoglobin (collection of blood approximately 20 h after cessation of exposure; alkaline hydrolysis). The determination revealed two-order of magnitudes higher yields of the biomarkers in urine when compared to hemoglobin. The concentration of analytes from the respective biological matrix was highly correlated with the airborne concentration of pMDI whilst their yields exhibited a reciprocal relationship to the airborne concentration of pMDI. A linear relationship could only be demonstrated by using a logarithmic transformation of data. With respect to the amount of 4,4'-methylenediphenyldianiline creatinine (MDA/g creatinine) in hydrolyzed urine of rats at an exposure level similar to the current workplace concentration of MDI, this marker of exposure was approximately 10-times lower in rats than predicted for humans. This suggests that the extrapolation of animal data to man as well as from one exposure regimen to another, without taking into consideration the different deposition/retention patterns of vapors (<or=0.05 mg/m(3)) or aerosols of MDI, might be error prone. In summary, taking into account previous and current experimental evidence, these data substantiate further that the formation of MDI-related biomarkers appear to be governed by spontaneously occurring, scavenging reactions at the portal-of-entry. Comparison of MDI with its corresponding amine support that the analytes determined stem from conjugated MDI rather than in vivo hydrolyzed MDI.

Pyrethroids used indoors--immune status of humans exposed to pyrethroids following a pest control operation--a one year follow-up study

A multiparametric analysis of immune components was performed in blood and serum of 61 voluntary persons before and after (1 day, 3 days, 4-6 months, 10-12 months) a professional pest control operation (PCO) using pyrethroids. Following parameters were included in the study (1) immunological parameters of the humoral defence, i.e. immunoglobulins of the classes A, G, M and E, complement components C3c and C4, acute phase proteins such as acid alpha 1-glycoprotein, haptoglobin, C-reactive protein; (2) mediators and receptors of immunity, i.e. neopterin, soluble interleukin-2 receptor (sIL-2R), soluble interleukin-6 receptor (sIL-6R), soluble tumor necrosis factor receptor (sTNF RII); (3) immunological markers of the cellular defence, i.e. white blood cell counts and lymphocyte (sub)populations such as total lymphocytes (CD2), mature lymphocytes (CD3), T-helper/inducer cells (CD4), T-suppressor/cytotoxic cells (CD8), B-cells (CD20), natural killer cells (CD56), as well as the ratio of CD4/CD8. The medians of all investigated immune components found before and for all time intervals after pyrethroid application were within the reference interval with respect to the total collective. Within this physiological range the investigated parameters showed a trend to lower values predominantly during the early phase (1 and 3 days) after PCO, partially being significant. Significant decreases were no more present in the late phase (6 to 12 month) after PCO indicating reversibility. Atopics did not differ in the immune response after PCO as compared to non-atopics. Obtained results suggest a modulation of immune components after a correct performed PCO within the physiological range towards lower values during the first days. However these immune changes are considered to be subtle and underlying compensatory mechanisms of immunoregulation.

Pyrethroids used indoors--biological monitoring of exposure to pyrethroids following an indoor pest control operation

A prospective epidemiological study with respect to pyrethroid exposure was carried out combining clinical examination, indoor monitoring and biological monitoring. The results of the biological monitoring are presented. Biological monitoring was performed in 57 persons before (T1) as well as 1 day (T2), 3 days (T3), 4-6 months (T4), and 10-12 months (T5) following a pest control operation (PCO) with pyrethroid containing products such as cyfluthrin, cypermethrin, deltamethrin or permethrin. Pyrethroids in blood were measured by GC-ECD. The respective metabolities cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (DCCA), cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (DBCA), 3-phenoxybenzoic acid (3-PBA) and fluorophenoxybenzoic acid (FPBA) were measured in urine using GC/MS. For all cases the concentrations of pyrethroids in blood were found to be below the detection limit of 5 micrograms/l before and after the PCO. With a detection limit of 0.2 microgram/l of the investigated metabolites, the percentage of positive samples were 7% for cis-DCCA, 3.5% for trans-DCCA and 5.3% for 3-PBA before PCO. One day after PCO (T2) the percentage of positive samples increased remarkably for cis-DCCA (21.5%), trans-DCCA (32.1%) and 3-PBA (25%) showing significantly increased internal doses as compared to pre-existing values. This holds also true for T3, whereas at T4 and T5 the significant increase was no more present. FPBA and DBCA concentrations were below the respective detection limit before PCO and also in most cases after PCO. In 72% of the subjects the route of pyrethroid uptake (measured by determining the DCCA isomeric ratio) was oral/inhalative and in 28% it was dermal. Based on the biological monitoring data it could be shown that appropriately performed pest control operations lead to a significant increase of pyrethroid metabolite concentration in the early phase (1 and 3 days) after pyrethroid application as compared to the pre-exposure values. However, evaluated metabolite concentrations 4-6 months after PCO did not exceed values of published background levels.

Beta-endorphin cells in the arcuate nucleus: projections to the supraoptic nucleus and changes in expression during pregnancy and parturition

Supraoptic nucleus oxytocin neurone activity and secretion are inhibited in late pregnancy and parturition by endogenous opioids. Here, we investigated alterations in the projections and gene expression of beta-endorphin/pro-opiomelanocortin neurones in the arcuate nucleus in the pregnant rat. All regions of the arcuate nucleus were found to contain cells immunoreactive for beta-endorphin fluorescent microbeads retrogradely transported from the supraoptic nucleus, and double-labelled neurones (beta-endorphin plus microbeads), showing that beta-endorphin neurones throughout the arcuate nucleus project to the supraoptic nucleus. There was an increase in the number of beta-endorphin-immunoreactive cells in the arcuate nucleus and an increase in the density of beta-endorphin fibres within the supraoptic nucleus and peri-supraoptic region in late pregnancy and parturition, suggesting enhanced expression of beta-endorphin and increased beta-endorphin innervation of the supraoptic nucleus. Pro-opiomelanocortin mRNA expression in the arcuate nucleus increased in late compared to early pregnancy: the number of positive neurones significantly increased in the caudal region. Fos expression (an indicator of neuronal activation) in the arcuate nucleus was colocalized in beta-endorphin neurones in both proestrus and parturient rats, but the number of positive cells did not increase during parturition, suggesting lack of activation of beta-endorphin neurones at birth. Thus, beta-endorphin cells in the arcuate nucleus project to the supraoptic nucleus and increased innervation during pregnancy may explain the enhanced endogenous opioid inhibition of oxytocin neurones.

Indoor pyrethroid exposure in homes with woollen textile floor coverings

In order to investigate human's exposure to permethrin from treated woollen textile floor coverings and possible adverse health effects, a study was carried out in 80 private homes in Hannover (Germany) equipped with woollen textile floor coverings (wool wall-to-wall carpets or woven or knotted rugs). For indoor monitoring, permethrin was determined both in house dust and on suspended particles. While permethrin concentrations in house dust (< 2 mm) were high (arithmetic mean: 53.7 mg/kg, 90th percentile 129.1 mg/kg), the permethrin concentrations in the air (suspended particles) were very low (arithmetic mean 2.8 ng/m3, 90th percentile 5.8 ng/m3, first sampling). Additional experiments demonstrate that permethrin on suspended particles result from carpet fiber abrasion (and not from an evaporation/re-condensation process). The internal exposure of the 145 inhabitants participating in the study was determined by biological monitoring (permethrin metabolites in urine). In a first sampling period almost 14% of the samples showed concentrations of the metabolite DCCA and almost 23% of the metabolite 3-PBA above the limit of detection (0.2 microgram/l). A model was developed which allows the calculation of the metabolite concentration in urine due to inhalative uptake of permethrin. Even for the worst case situation the calculated metabolite concentrations were ca. 30 times lower than the experimental results. The observed concentrations of metabolites are comparable to those of the background concentrations of the general population in Germany, suggesting that they must origin from other sources than woollen textile floor coverings. The indoor and biological monitoring data as well as the evaluation of the reported symptoms give no indication of an adverse health effect due to carpet treatment by permethrin.

Polymorphism of glutathione S-transferases and susceptibility to acrylonitrile and dimethylsulfate in cases of intoxication

In this paper, the difficulties of genetic screening of occupationally exposed subjects for the evaluation of retrospective, and prospective, health risk assessments is illustrated with reference to glutathione S-transferase (GST) function. Individual differences in the magnitude and half-life of adduct levels, derived from background and occupational exposure, are observed largely independently of genetically determined conjugator status. During detoxification, GSTs play a critical role in providing protection against electrophiles and products of oxidative stress. GSTs are a superfamily of enzymes that may have broad and overlapping substrate specificities. Deficiencies of GST isoenzymes may be compensated by the presence of other isoforms and by the use of alternative metabolic pathways. This may be one reason for the abundance of controversial data on GST polymorphisms and adverse health effects.

The importance of oxytocin mechanisms in the control of mouse parturition

The role of oxytocin in parturition in mice was investigated. Pup birth profiles, blood samples and brains were collected from parturient mice observed under red light conditions in a reversed light:dark photoperiod. Peripheral administration of an oxytocin antagonist in a dose-dependent manner delayed the birth of subsequent pups, indicating that oxytocin is required for a normal pup birth profile. Oxytocin neurones were activated during birth as shown by both increased immediate early gene ( Fos) expression in oxytocin neurones in the supraoptic nucleus and increased plasma oxytocin concentrations during birth. In addition, the nucleus of the tractus solitarius and the olfactory bulbs, sites that process inputs to oxytocin neurones, become activated during parturition. Exposure to stress during parturition halted subsequent deliveries; at this stage plasma oxytocin concentrations were not higher than those of virgin mice, and birth was restored by administration of oxytocin. Administration of beta-adrenergic antagonist (propranolol) also restored stress-delayed birth, whereas administration of ritrodrine (beta-agonist) delayed birth in non-stressed mice, indicating that adrenergic mechanisms contribute to stress-delayed births in mice. Administration of morphine (mu-opioid agonist) delayed births transiently, but naloxone (opioid antagonist) did not prevent stress-delayed birth, indicating that endogenous opioids do not appear to contribute to neuroendocrine or uterine mechanisms that promote birth in mice. Therefore, despite evidence in oxytocin knockout mice that oxytocin is not essential for parturition in this species, the results of the present study indicate that oxytocin neurone activity and secretion contribute to the birth process in normal mice.