Acute toxicity of two pyrethroids,permethrin, and cypermethrin in neonatal and adult rats

The present study aims specifically at obtaining a comparison of the acute toxicity of cypermethrin (CY), a type I pyrethroid, and permethrin (PERM), a type II pyrethroid, administered orally as a single dose to neonatal and adult rats, and at assessing the importance of pyrethroid biotransformation in CY and PERM toxicity through use of drug metabolism inhibitors. Our experiments show that CY is more toxic than PERM to adult and neonatal rats. The sensitivity of neonatal rats both to CY and to PERM toxicity is higher, the younger the animals. CY is much more toxic than PERM in the neonatal rat, compared with the adult. In rats aged 8, 16, and 21 days, pretreatment with piperonil butoxide (PB), a monooxygenase inhibitor, or with tri-o-tolyl phosphate (TOTP), an esterase inhibitor, does not produce significant variations in the lethal effects of CY and PERM. Instead, in the adult rats, a significant increase in CY (X²=5.97;p<0.05) and PERM (X²=4.37;p<0.05) mortality occurred in rats pretreated with esterase inhibitors, whereas no increase in CY and PERM toxicity was found in adult animals pretreated with monooxygenase inhibitor. It was concluded that the higher level of sensitivity of the neonate rat to pyrethroid toxicity is probably due to incomplete development of the enzymes which catalyze the metabolism of pyrethroids in the liver of young animals. It is suggested that ester hydrolysis is an important pyrethroids detoxification reaction in the adult rat.     

Postnatal development of dopamine receptor expression in rat peripheral blood lymphocytes.

Postnatal development in the expression of dopamine D1-like and D2-like receptors was investigated in peripheral blood lymphocytes of male Wistar rats aged 1, 3, 4, 8, 12 and 16 weeks of age by radioligand binding assay techniques. Sample of frontal cortex, striatum and hippocampus were also investigated as reference tissues. The dopamine D1-like receptor antagonist [3H]SCH 23390 and the dopamine D2-like receptor agonist [3H]7-OH-DPAT were used as radioligands. The affinity (K(d)) of [3H]SCH 23390 or of [3H]7-OH-DPAT binding was unchanged in lymphocytes of rats of different age groups. The density (B(max)) of [3H]SCH 23390 binding sites increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 8th week of age, and then increased slightly at 12 and 16 weeks of age. The B(max) value of [3H]7-OH-DPAT binding to lymphocytes increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 4th week, increased again until the 12th week and then plateaued. Dopamine D1-like and D2-like receptor maturation in frontal cortex, hippocampus and striatum revealed an increased receptor density until the 4th week of age and a relative stabilization of receptor density values between the 4th to the 12th week depending on the area considered. Comparatively postnatal maturation of lymphocyte dopamine D1-like receptors displayed a pattern different from that of brain areas investigated, whereas maturation of D2-like receptors displayed a pattern similar to that of striatum. The quantitative and/or qualitative dissimilarities between development of lymphocyte and brain dopamine receptors suggest that from a developmental point of view lymphocyte dopamine receptors probably cannot be considered as a marker of homologous brain receptors.     

Selective blockade of muscarinic M2 receptors in vivo by the new antagonist tripitramine

The antimuscarinic effects of tripitramine (1, 1, 24--tris [[5, 11-dihydro-6-oxo-6H-pyrido [2, 3-b][1, 4]-benzodiazepin-11-yl)(carbonyl] methyl]-8, 17-dimethyl-1, 8, 17, 24-tetraazatetracosane tetraoxalate), a member of a series of polymethylene tetraamines with in vitro cardioselectivity, were assessed in two in vivo preparations: anaesthetized and pithed rats. The well-known M₂ selective antagonist methoctramine was used in a comparative study. Tripitramine (0.0202 mol/kg i.v.) proved to be a potent antagonist at cardiac M₂ receptors that mediate the decrease in heart rate in the pithed rat; the same dose of this antagonist in the anaesthetized rat did not significantly affect the depressor action of methacholine mediated by vascular M₃ receptors. In the pithed rat, this dose did not affect the ganglionic M₁ receptor-mediated tachycardia and pressor response to muscarme or McN-A-343. These in vivo data are consistent with the in vitro findings and confirm that tripitramine is a more potent and selective muscarinic M₂ receptor antagonist than methoctramine.     

Dopaminergic system modulation, behavioral changes, and oxidative stress after neonatal administration of pyrethroids

Pyrethroids are a class of insecticides involved in different neurological disorders. They cross the blood-brain barrier and exert their effect on dopaminergic system, contributing to the burden of oxidative stress in Parkinson's disease through several pathways. The aim of the present study was to evaluate the effect of neonatal exposition to permethrin and cypermethrin (1/10 of DL(50)) in rats from the eighth to the fifteenth day of life. Open-field studies showed increased spontaneous locomotor activity in the groups treated with permethrin and the one treated with cypermethrin, while a higher number of center entries and time spent in the center was observed for the cypermethrin-treated group. Lower dopamine and higher homovanillic acid levels were measured in the striatum from both treated groups. A reduction of blood glutathione peroxidase content was measured, while no change in blood superoxide dismutase was observed. Carbonyl group formation increased in striatum, but not in erythrocytes. Lipid peroxidation occurred in erythrocytes, but not in striatum. No changes in fluidity at different depths of plasma membrane were measured in striatum or erythrocytes. The activation of monocyte NADPH oxidase by phorbol esters (PMA) shows that superoxide anion production was reduced in the pyrethroid-treated groups compared to the control group. Our studies suggest that neonatal exposition to permethrin or cypermethrin induces long-lasting effects after developmental exposure giving changes in open-field behaviors, striatal monoamine level, and increased oxidative stress. Although the action of pyrethroids on various target cells is different, a preferential interaction with the extracellular side of plasma membrane proteins can be observed.     

Lack of Polarized Type 1 or Type 2 Cytokine Profile in Asymptomatic HIV-1-Infected Patients During a Two-Year Bimonthly Follow-Up

The production of type 1 (interferon or IFN-γ) and type 2 (interleukin or IL-4 and IL-10) cytokines by mitogen-stimulated peripheral blood mononuclear cells (PBMCs) obtained from asymptomatic human immunodeficiency virus-seropositive (HIV⁺) patients untreated with any antiviral, antibacterial or antimycotic drugs, and from healthy individuals, was evaluated by quantitative ELISA. Patients who were HIV⁺ were characterized by the absence of abnormal cytokine production. The level of each cytokine differed among individuals in the same group with intersubject variations greater for HIV⁺ patients than for healthy individuals. The longitudinal evaluation of IFN-γ, IL-4 and IL-10 production showed intrasubject variations which were particularly marked in HIV⁺ patients. Accordingly, HIV⁺ patients and, to a lesser extent, healthy individuals were characterized by a wide spectrum of possible profiles, which were confined to type 0 phenotype. In HIV⁺ patients no correlation was found between each cytokine level and the number of CD4⁺ T cells, not even in those with a falling CD4⁺ T-cell count and clinical symptoms.     

Contribution of CD4+, CD8+CD28+, and CD8+CD28- T cells to CD3+ lymphocyte homeostasis during the natural course of HIV-1 infection.

The relationship between the number of circulating CD4+ T cells and the presence of particular CD8+ T cell subsets was analyzed by flow cytometry on PBL from asymptomatic HIV-1-infected patients whose specimens were collected every 2 mo for a total period of 32 mo. Only slight variations were detected in the absolute number of lymphocytes and percentage of CD3+ lymphocytes, whereas both CD4+ and CD8+ T cell subsets showed wide intrapatient variation. Variations in the number of CD8+CD28+ cells paralleled those of the CD4+ T cell subset in each patient tested, while the presence of CD8+CD28- T cells correlated inversely with CD4+ and CD8+CD28+ T cells. These data show that changes in the number of circulating CD4+-and CD8+CD28+ T cells are strongly related to the presence of CD8+CD28- T cells in these patients. Insight into the significance of CD8+CD28- T cell expansion will allow us to understand the mechanisms and significance of the HIV-1- driven change in CD4+CD8+ T cell homeostasis and the basic immunopathology of HIV disease.     

Inhibitory effect of calcitonin on growth hormone and insulin secretion in man

The effect of calcitonin administration on basal and arginine-stimulated growth hormone and insulin plasma levels was investigated. The intramuscular injection of synthetic salmon calcitonin (100 U MRC) in five normal subjects produced a significant decrease (p less than 0.05) in insulin concentration. The same amount of calcitonin given 15 min before an arginine infusion test in seven normal subjects significantly reduced the response of growth hormone (p less than 0.025) and insulin (p less than 0.005) to the stimulus.     

Effect of methyldopa on prolactin serum concentration

Summary In a group of ten hypertensive patients, the effects of methyldopa administration in two different formulations on serum prolactin (PRL) were studied. A single oral dose of normal release methyldopa significantly increased serum prolactin levels, peak concentrations occurring 3 to 6 h after drug administration. On the contrary, administration of sustained release methyldopa at the same dose was only followed by slight and not significant fluctuations in prolactin plasma levels. Both formulations produced a significant decrease of systolic and diastolic blood pressures, without significant differences between sustained and normal release methyldopa effects.     

Alterations in rabbit aorta induced by types I and II pyrethroids

Since pyrethroids are involved in reactive oxygen species production and no investigations have yet been performed on smooth muscle cell integrity, we studied the influence of permethrin- and cypermethrin-treatment on rabbit aorta using confocal laser scanning fluorescence microscopy, which allows cell viability to be assessed within the wall of living rabbit aorta. The data obtained show that the pyrethroid-treatment (10-100μM) impairs the smooth muscle cell viability. A double-labeling protocol allowed us to distinguish cytotoxic effects of permethrin- and cypermethrin-treatment in aortic rings. In conclusion, permethrin seems to induce more oxidative stress on the aorta wall than that cypermethrin does.