Toxicokinetics and tissue distribution of prothioconazole in male adult Sprague-Dawley rats following a single oral administration

Abstract

1. Prothioconazole (PTC) is a new type of triazolinthione fungicide used worldwide. Despite its widespread use, the basic toxicokinetics (TK) information for health risk assessments of PTC is limited.

2. TK behavior and metabolism studies of PTC were performed in male adult Sprague Dawley (SD) rats after a single oral administration. Serial blood and tissue samples were analyzed for their PTC content by high-performance liquid chromatography (HPLC) to obtain comprehensive time-course data for estimation of TK parameters.

3. PTC was rapidly but incompletely absorbed from the gastrointestinal tract of fasted adult rats. It was widely distributed in all parts of body, but demonstrated little tendency to accumulate. And PTC was excreted mainly in the form of parent compound.

4. The detection of PTC in brain and testis proved that further investigations are required to determine whether PTC could result in neurotoxicity and male reproductive toxicity.     

Electrophilic tissue burden in male Sprague-Dawley rats following repeated exposure to binary mixtures of polycyclic aromatic hydrocarbons

The aim of this study was to investigate the electrophilic tissue burden (ETB) formation, assessed as covalent binding of the ultimate carcinogen benzo(a)pyrene diolepoxide (BaPDE) with cellular proteins, in liver, lung and heart, as well as with haemoglobin (Hb) following repeated exposure to binary mixtures of benzo(a)pyrene (BaP) and pyrene (P). Male Sprague-Dawley rats were injected intraperitoneally, once daily for 10 consecutive days, with binary mixtures of BaP and P in three different exposure scenarios corresponding to BaP/P ratios of 0.2, 1 and 5 and with three dose levels of BaP (2, 6 and 20 mg/kg) for each scenario. ETB levels were measured as the ultimate analyte benzo(a)pyrene tetrol (BaPTeT) obtained after mild acid hydrolysis of BaPDE-adducts with proteins. A high-performance liquid chromatography fluorescence technique was used to quantify the analyte. Similar ETB levels (within a factor of 4) were observed in all tissues studied at any given binary dose. However, the ETB generally tended to be somewhat higher in metabolically active tissues (i.e. liver and lung) than in metabolically non-active tissues (i.e. heart and Hb). Lack of influence of pyrene on ETB levels in all tissues was confirmed over the binary dose range examined. Linear BaP-dose-dependent ETB formation in all tissues (at P0.05) was observed. Linear regressions were found for all between-tissue relationships of ETB over the exposure doses, with best linear correlations obtained for ETB in heart versus Hb (R ²=0.709; P<0.0001) and ETB in lung versus Hb (R ²=0.507; P<0.0001). The results thus suggest that BaPDE–Hb adducts could serve as a surrogate of the ETB, namely in tissues that are potential targets for carcinogenicity such as lung. The results obtained in this study indicate the role of the ETB as a promising molecular biomarker of the potential cellular damage resulting from intracellular covalent binding in animal studies.     

Pharmacokinetics of inhaled manganese phosphate in male Sprague-Dawley rats following subacute (14-day) exposure

Methylcyclopentadienyl manganese tricarbonyl (MMT) is used as a gasoline octane enhancer. Manganese phosphate is the primary respirable (PM(2.5)) MMT-combustion product emitted from the automobile tailpipe. The goal of this study was to determine the exposure-response relationship for inhaled manganese phosphate in adult male CD rats. Rats were exposed 6-h/day for either 5 days/week (10 exposures) or 7 days/week (14 exposures) to manganese phosphate at 0, 0.03, 0.3, or 3 mg Mn/m(3) (MMAD congruent with 1.5 micrometer). The following tissues collected at the end of the 2-week exposure: plasma, erythrocytes, olfactory bulb, striatum, cerebellum, lung, liver, femur, and skeletal muscle (n = 6 rats/exposure group) were analyzed for manganese content by neutron activation analysis. Intravenous (54)MnCl(2) tracer studies were also conducted following the 14th exposure (n = 6 rats/concentration), and whole-body gamma spectrometry was performed immediately after injection and at 1, 2, 4, 8, 12, and 16 weeks after (54)MnCl(2) administration. Increased manganese concentrations were observed in olfactory bulb, lung, femur, and skeletal muscle following exposure to 3 mg Mn/m(3) (10 or 14 exposures). Increased manganese concentrations were also observed in olfactory bulb, striatum, and lung following exposure to 0.3 mg Mn/m(3) (14 exposures only). Red blood cell and plasma manganese concentrations were increased only in rats exposed to 3 mg Mn/m(3) (10 exposures). Rats exposed to 3 mg Mn/m(3) also had an increased whole-body manganese clearance rate when compared to air-exposed control animals. Our results suggest that the rat olfactory bulb may accumulate more manganese than other brain regions following inhalation exposure.     

Toxicokinetics of 14C-endosulfan in male Sprague-Dawley rats following oral administration of single or repeated doses

Endosulfan (ES), an organochlorine (OC) insecticide that belongs to the cyclodiene group, is one of the most commonly used pesticides to control pests in vegetables, cotton, and fruits. The toxicokinetics of 14C-endosulfan following oral administration of a single dose of 5 mg/kg body weight was investigated in male Sprague-Dawley rats. Three rats were sacrificed 30 min, 1 h, 2 h, 4 h, and 8 h after dosing. 14C-endosulfan radioactivity was detected in all tissues at each time point. In a separate experiment urine and feces were collected for 96 h. The total radioactivity recovered in the excreta for 4 days was 106.8% +/- 26.2%, with fecal elimination the major route of elimination route (94.4% +/- 21.4%). The cumulative excretion in the urine for 4 days was 12.4% +/- 4.8%. Radioactivity 8 h after administration was highest in gastrointestinal (GI) tract tissue (20.28 +/- 16.35 mg ES eq./L) and lowest in muscle (0.18 +/- 0.06 mg ES eq./L). The toxicokinetic parameters obtained from 14C-endosulfan-derived radioactivity in blood were distribution half-life (T1/2 x) = 31 min and terminal elimination half-life (T1/2 y) = 193 h. Blood concentration reached its maximum (Cmax) of 0.36 +/- 0.08 mg ES eq./L 2 h after the oral dose. Endosulfan was rapidly absorbed into the GI tract in rats, with an absorption rate constant (ka) of 3.07 h(-1).     

Disposition of lead (Pb) in saliva and blood of Sprague-Dawley rats following a single or repeated oral exposure to Pb-acetate

Biological monitoring for lead (Pb) is usually based upon a determination of blood Pb concentration; however, saliva has been suggested as a non-invasive biological matrix for assessing exposure. To further evaluate the potential utility of saliva for biomonitoring, the disposition of Pb was evaluated in whole blood (WB), red blood cells (RBC), plasma, parotid gland, bone, and saliva following either a single oral dose of 100mg Pb-acetate/kg body weight in rats or approximately 1-week after 5 sequential daily oral gavage doses of 1, 10, or 100mg Pb-acetate/kg/day. Saliva volume, pH, total saliva protein, and alpha-amylase activity were also determined. At specified times post-dosing groups of animals were anesthetized and administered pilocarpine to induce salivation. Saliva was collected, the animals were humanely sacrificed, and tissue samples were likewise collected, weighed, and processed for Pb analysis. Following a single dose exposure to Pb-acetate, Pb was detectable in all samples by 30 min post-dosing. For both the single and repeated dose treatments the concentration of Pb was highest in WB and RBC relative to plasma and saliva. However, the Pb rapidly redistributed (within 5-days post-treatment) from the blood into the bone compartment based on the substantial decrease in WB and RBC Pb concentration, and the concurrent increase in bone Pb following repeated exposure at all dose levels. Although there is clear variability in the observed Pb concentrations in plasma and saliva, there was a reasonable correlation (r(2)=0.922) between the average Pb concentrations in these biological matrices, which was consistent with previous observations. The single oral dose of Pb-acetate resulted in a decrease in salivary pH which recovered by 24h post-dosing and a decrease in alpha-amylase enzyme activity which did recover within 5-days of ceasing exposure. It is currently unclear what impact these slight functional changes may or may not have on Pb salivary clearance rates. These results demonstrate a feasibility to rapidly detect Pb in saliva and suggest that saliva may correlate best with plasma Pb concentration.     

Pregnancy outcomes following pre- and post-implantation exposure of Sprague-Dawley rats to benzyl isothiocyanate.

The present investigation examines the outcomes of rats' pregnancy following pre- and post-implantation maternal exposure (orally) to benzyl isothiocyanate (BITC; 12.5, 25 and 50 mg/kg body weight). Three maternal deaths were recorded in the group of rats treated with 50 mg/kg BITC. Obvious signs of toxicity characterized by hypo-activity, perinasal staining, piloerection, hunched posture and decrease in body weights were observed in BITC-treated rats during the treatment periods. Dose-dependent increase in early fetal resorptions was seen in rats treated with BITC prior to implantation, but was not statistically significant. There were no significant differences in the number of implantation sites in treatment groups compared with the control. Similarly, there were no significant differences in the number of fetal resorptions, relative weights of maternal liver, kidney and spleen of rats in post-implantation treatment groups compared with the control. The differences in the number of viable fetuses in treatment groups compared with the control were also not significant. However, fetal weights in rats treated with 25 and 50 mg/kg BITC and placental weights in all the treatment groups were significantly lower than the control. In conclusion, at 12.5-50 mg/kg, BITC did not cause significant pre- and post-implantation fetal loss in pregnant rats. BITC-induced low fetal and placental weights could be of obstetrical importance, but at levels/doses that would provoke maternal toxicity.     

Immunotoxic effects of 2-bromopropane in male Sprague-Dawley rats: a 28-day exposure study

Immunotoxic effects of 2-bromopropane were investigated in male Sprague-Dawley rats. The rats were treated orally daily with 2-bromopropane at 100, 330, or 1000 mg/kg for 28 consecutive days. Four days before necropsy, the rats were immunized intravenously with sheep red blood cells (SRBCs). The body and thymus weights were significantly reduced by treatment with 2-bromopropane at the highest dose. In addition, the numbers of splenic and thymic cells were decreased by 2-bromopropane. In hematology, the numbers of white blood cells, red blood cells, and platelets were significantly reduced. Among the serum clinical parameters, the levels of chloride ion were significantly increased by 2-bromopropane. The antibody response to SRBCs was significantly suppressed at the highest dose. With immunized animals, immunophenotyping of splenic and thymic cells was performed to investigate the changes of the number of macrophages, B cells, and T cells in spleen and the number of CD4+ and CD8+ cells in thymus. The numbers of most cell types were significantly decreased in the spleen when animals were treated with 2-bromopropane at 1,000 mg/kg. Likewise, all cell types of thymus were significantly decreased by 2-bromopropane. The present results suggest that 2-bromopropane may have an immunotoxic potential in male Sprague-Dawley rats when the rats are exposed for 28 d.     

Changes in androgen-mediated reproductive development in male rat offspring following exposure to a single oral dose of flutamide at different gestational ages.

Previous studies have indicated that the androgen receptor antagonist, flutamide, can produce a suite of reproductive malformations in the male rat when orally administered daily on gestation days (GD) 12-21. The objective of this study was to investigate the gestation time dependence for the induction of these malformations to establish a robust animal model for future studies of gene expression related to specific malformations. Groups of timed-pregnant Sprague-Dawley rats (GD 0 = day of mating) were administered flutamide as a single gavage dose (50 mg/kg) on GD 16, 17, 18, or 19 with 10 dams per group. Control animals (5 dams per time per group) were administered corn oil vehicle (2 ml/kg). Dams were allowed to litter, and their adult male offspring were killed at postnatal day (PND) 100 +/- 10. Anogenital distance was measured at PND 1 and 100. Areolae were scored at PND 13, and permanent nipples evaluated at PND 100. No reproductive tract malformations were found in control male offspring. In the treated groups, malformations were noted following exposure at every GD, although the incidence of specific malformations varied by GD. At GD 16, the highest incidence was noted for permanent nipples (46% pups, 60% litters), epispadias (12% pups, 30% litters), and missing epididymal components (5% pups, 20% litters). The highest incidences for hypospadias (58% pups, 80% litters), vaginal pouch (49% pups, 70% litters), cleft prepuce (29% pups, 60% litters), and missing prostate lobes (12% pups, 60% litters) were noted at GD 17. At GD 18 the highest incidence of malformations noted were epispadias (5% pups, 30% litters), reduced prostate size (32% pups, 90% litters), and abnormal kidneys (3% pups, 30% litters) and bladders (7% pups, 30% litters), while on GD 19 70% of the litters had animals with abnormal seminal vesicles. Testicular and epididymal morphological changes were noted at all GDs and were consistent with the gross observations and peaked in incidence and severity on GD17. The major discrepancy between this study and previous multiple-dose studies was in the very few numbers of animals presenting with cryptorchidism (only one each on GDs 16 and 17), suggesting that exposure over multiple days may be required to induce this malformation. Thus, a single gestational exposure of flutamide induced numerous reproductive tract malformations consistent with previously reports following multiple exposures, with the timing of the exposure producing marked tissue selectivity in the response noted in adult offspring.     

Different pattern of metastasis in liver implanted pancreatic cancer between young and old Syrian golden hamsters

We have previously reported on the "return trip" metastases from the liver to the pancreas in a hamster experimental pancreatic cancer model. Because the pancreas is the main metastatic site of liver-implanted pancreatic tumors, our aim was to clarify whether the metastatic sites differ in young and old tumor-bearing animals. HaP-T1, a continuous tissue-cultured cell line, derived from BHP-induced pancreatic adenocarcinoma, was implanted into the liver. The animals were divided into two groups: A) younger than 26 weeks and B) older than 26 weeks. Three animals from each group were sacrificed on Days 35, 42, 49, 56, 63, 70, 77, 84, 91 and 98, to study the metastatic sites. Survival was also studied. After death, necropsy was performed. Resected and necropsied specimens were analyzed histopathologically and by PCR/RFLP analysis to confirm the presence of K-ras point mutation. The success rate of implantation was 100%. Survival was 102.3+/-2.5 days in group A and 95.3+/-1.5 days in group B. Animals of group A, sacrificed weekly until Day 70, showed metastases only to the pancreas ("return trip"), while this phenomenon happened only in animals sacrificed on Day 35 in group B. In group A, on Days 77, 84, 91 and 98, metastases were also found in the kidneys, lymph nodes, ovary and testis. In hamsters of group B, metastases were found in multiple sites such as the pancreas, vas deferens, ovary and testis ("multiple journeys"). All intra-hepatically-implanted tumor and metastatic sites showed the K-ras point mutation. This homologous implantation model may be helpful for further research into the process of metastasis and its relationship with the immunological response.     

Clearance of cyclopentyladenosine and cyclohexyladenosine in rats following a single subcutaneous dose.

A(1)-adenosine receptor agonist N(6)-cyclopentyladenosine (CPA) (3.0 mg kg(-1) body weight), or N(6)-cyclohexyladenosine (CHA) (3.0 mg kg(-1) body weight) was subcutaneously (s.c.) administered as a single dose to rats. After that, the blood samples (150 microl) were collected from vena saphena into heparinized capillary tubes at the different time points. The concentrations of CPA and CHA were assayed by reversed-phase high performance liquid chromatography (HPLC). Based on the present study, the retention times for CPA and CHA were 3.029 +/- 0.017 min and 5.07 +/- 0.031 min, respectively. In addition, the maximum concentrations of CPA and CHA were measured 60 and 80 min after the administration, and the half-lives of these compounds in the circulation were approximately 48.5 +/- 4.4 min and 106.6 +/- 7.4 min, respectively. Presumably, the difference between these values due to the larger cycloalkyl substituent of CHA and different absorption properties of these compounds. Moreover, in the present study, the elimination half-life was approximately sevenfold longer than that previously reported for CPA (48.5 +/- 4.4 min versus 6.9 +/- 0.5] min). The discrepancy in the half-life is not surprising because the administration route was different. On the other hand, after the s.c. administration, the absorption rates of these adenosine analogues are known to be slow. Based on the results of this paper, the authors conclude that the half-life of CHA is approximately 2.2-fold compared to that of CPA.     

Gestational and lactational transfer of melamine following gavage administration of a single dose to rats

Melamine contamination in an infant formula manufactured by a firm in China was reported in September 2008. Maternal transfer of melamine during pregnancy and through breast-feeding are possible ways of introduction. This study aims to evaluate the maternal transfer of melamine into amniotic fluid and breast milk through oral intake by pregnant and lactating rats, respectively. The quantity of melamine in the dam’s sera, amniotic fluid, breast milk as well as in fetal whole body extract was measured. Our results showed that, after administration of single dose of 21.4 mg/kg per body weight of melamine to pregnant rats (16-18 days of gestation) by gavage, about 80% of melamine was found in dam’s serum in 0.5 h. Melamine further reached the fetuses through placental transfer as it was found that peak melamine level of 7.15 ppm (∼30%) was detected in the fetuses after 2 h and 4.36 ppm (∼20%) was shown in amniotic fluid after 3 h of maternal intake. In the lactating rats, about 40% of maternal intake of melamine was transferred to breast milk and peaked at 3 h. The results of this study confirmed the maternal transfer of melamine to fetuses in utero and infants through breast feeding.     

Quantitating exposure to chemical carcinogens: in vivo alkylation of hemoglobin by benzo[a]pyrene

Mild acid hydrolysis of globin preparations from erythrocytes of mice, previously exposed topically to benzo[a]pyrene (BaP), releases tetrols which are detectable by HPLC/fluorescence analysis. If the mouse is exposed to radiolabelled BaP, radioactivity can be found in the acid-releasable tetrols. Treatment of the globin preparations prior to acid hydrolysis with proteolytic enzymes, but not enzymes that degrade nucleic acids, followed by dialysis, reduces the amount of tetrols that can be detected. Because the procedure used for the isolation of globin preparations from mouse blood precludes the presence of non-covalently bound BaP or its cellular metabolites, it is concluded that prior to acid hydrolysis, the tetrols were covalently attached to the hemoglobin, most probably as a result of the metabolic conversion of the applied carcinogen to the chemically reactive anti-diol epoxide. There is a dose response relationship between the amount of BaP applied to the skin of the mouse and the occurrence, 24 h later, of BaP adducts to hemoglobin, while the adduct, once formed, disappears with a half-life of 6 days. The amount of anti-benzo[a]pyrene diol epoxide (anti-BaPDE) binding to DNA and hemoglobin at various doses of BaP appears to be qualitatively similar.     

Mecamylamine elicits withdrawal-like signs in rats following a single dose of nicotine

Rationale

The ability of nicotine to induce dependence (result in a withdrawal syndrome) is typically thought to require long-term, daily smoking. Emerging evidence suggests that symptoms of nicotine withdrawal may occur following only a few cigarettes. Whether acute exposure to nicotine can induce dependence in animals has not been well established.

Objective

The objective of this paper is to examine whether the nicotinic acetylcholine receptor antagonist mecamylamine elicits withdrawal-like signs in rats following acute nicotine exposure.

Methods and Results

Mecamylamine (3.0 mg/kg, s.c.) administered ≈2 h after a single dose of nicotine (0.5 mg/kg, s.c.) elicited increases in intracranial self-stimulation (ICSS) thresholds and somatic signs, two well-established effects of withdrawal from long-term (chronic) nicotine exposure. The magnitude of these effects remained constant across five daily test sessions. A lower dose of mecamylamine (1.5 mg/kg, s.c.) had little or no effect on ICSS thresholds or somatic signs following acute nicotine exposure, but precipitated robust increases in these measures during a chronic nicotine infusion. Finally, rats exhibited a small increase in ICSS thresholds over time following a single nicotine injection (0.5 mg/kg, s.c.), possibly reflecting a modest spontaneous withdrawal-like effect.

Conclusions

Mecamylamine elicited withdrawal-like signs in rats following a single dose of nicotine. The different effects of mecamylamine 1.5 mg/kg following acute versus chronic nicotine exposure supports the notion that these models simulate the early and more advanced stages of nicotine dependence, respectively. While further optimization and validation of these models is necessary, they may provide a novel approach for studying the earliest stages of nicotine dependence.     

Differences in performance between Sprague-Dawley and Fischer 344 rats in positive reinforcement tasks

This experimental investigation tested two different strains of rat, Sprague-Dawley (SD) and Fischer 344 (F344), in their ability to learn lever pressing for food (autoshaping) or intracranial self-administration (ICSA) of dextroamphetamine (AMPH) into the nucleus accumbens (NAcc). Additionally, a unique method of intracranial drug delivery was utilized, via reverse dialysis, by the use of a microdiaylsis probe. The experiments revealed definite behavioral differences between SD and F344 animals. The autoshaping data indicated that SD rats, on average, acquired lever pressing for food in fewer training days than F344 rats. Also, the ICSA experiment revealed that SD rats self-administered AMPH at a 30 mug/mul concentration. Lever pressing was significantly greater in those SD rats receiving AMPH than in the F344 drug group. Furthermore, the F344 rats never acquired lever pressing for intra-NAcc delivery of AMPH under our testing regime. These data reveal differences in performance of positively reinforced operant tasks between the inbred F344 rats as compared to the outbred SD strain.     

Differences in vulnerability to nicotine-induced kindling between female and male periadolescent rats

Rationale

It has recently been reported that chronic nicotine administration at subconvulsive doses causes seizures, a phenomenon referred to as kindling. Evidence points to the involvement of oxidative stress in pharmacological and electrical kindling, sex is known to influence the brain’s response to nicotine.

Objectives

This study investigated the sex differences in vulnerability to nicotine-induced kindling and the involvement of oxidative stress in this phenomenon.

Methods

Male and female periadolescent Wistar rats received repeated injections of a subconvulsive dose of nicotine (hemisulfate salt; 2 mg/kg, i.p.) every weekday for up to 25 days. To better understand the influence of oxidative stress in nicotine kindling, the antioxidant vitamin E (200 and 400 mg/kg, p.o.) was administered prior to nicotine administration. The levels of gluthatione (GSH), superoxide dismutase (SOD) activity, and lipid peroxidation were determined in the hippocampus (HC), prefrontal cortex (PFC), and striatum.

Results

Female animals developed kindling more rapidly than male rats. In female rats, kindling was associated with decreases in antioxidant defenses, including GSH levels in the HC and striatum and SOD activity in the PFC and striatum, and increased lipid peroxidation in all brain areas studied. By contrast, male kindled animals presented only with a decrease in the GSH in the HC. Vitamin E prevented the occurrence of kindled seizures by 80 % and 75 % in male and female rats, respectively.

Conclusion

These novel findings indicate that female periadolescent rats develop nicotine-kindled seizures earlier than their male counterparts. Differences in the oxidative balance may be involved in this mechanism.     

Mechanisms in cardiovascular regulation following chronic exposure of male rats to inorganic mercury

In this study we verified the possibility that chronic exposure to inorganic mercury may induce hemodynamic changes in the rat by affecting some neurogenic and/or humoral mechanisms regulating cardiovascular function. For this reason, aortic blood pressure, maximum rate of rise of the left ventricular pressure, heart rate, and electrocardiogram were monitored under pentothal anesthesia in rats which received 50 μg/ml of mercury (as HgCL₂) in drinking water for 320 days and in control rats. No pressor or electrocardiographic changes were found in mercury-treated animals, which showed increase of cardiac inotropism and decrease of the pressor and inotropic responses to bilateral carotid occlusion. Cardiovascular responses to bilateral vagotomy and iv hexamethonium under vagotomy were unchanged in the mercury-exposed rats. In these animals both pressor and inotropic responses to iv norepinephrine and to higher doses of epinephrine were reduced, while the vascular beta-adrenergic response to 0.125 μg/kg of iv epinephrine was potentiated. cardiovascular responses to acetylcholine, angiotensin I, angiotensin II, bradykinin, histamine, and serotonin did not differ in the two groups of rats. These results indicated that chronic mercury exposure affects cardiovascular function by interfering with the baroreflex mechanisms and/or the reactivity to catecholamines. Higher amounts of mercury were found in kidney, but the metal was significantly accumulated also in urine, blood, and brain. Mercury exposure greatly increased the levels of copper and zinc, but not that of iron, in brain and kidney. The increased accumulation of copper and zinc in tissues may be related in part to the mercury-induced synthesis of metallothionein, a protein able to bind these essential metals. It may be suggested that zinc and copper interact with mercury in inducing cardiovascular changes.     

Initial and residual toxicity following acute exposure of developing male rats to dibromochloropropane

Male Fischer 344 rats were given a single, sc injection of 1,2-dibromo-3-chloropropane (DBCP) at 6 or 25 days of age. One group of treated animals was killed 1 to 3 days afterward to compare the dose and time relationships of the acute toxic response of neonatal and weanling male rats to DBCP and another group at approximate sexual maturity (approximately 120 days of age) to detect residual toxic effects resulting from acute exposure. The 6-day-old rats were more susceptible than the 25-day-old rats to the acute toxic effects of DBCP, as characterized by reduced 48-hr survival, renal dysfunction, and renal and hepatic necrosis over the dose range of 80 to 320 mg/kg. The lowest dose tested, 20 mg/kg, and all higher doses reduced subsequent body and gonadal weight gains, and caused hypospermatogenesis or seminiferous tubular atrophy in animals exposed at 6 days of age and killed at sexual maturity. Similar effects were observed in animals exposed at 25 days of age, except that doses of 160 mg/kg or greater were required to produce residual toxic effects. These data indicate enhanced susceptibility of neonatal male rats to the gonadotoxic effects of dibromochloropropane, including the possibility of apparent irreversible injury caused by acute exposure.     

Acute and long-lasting cardiac changes following a single whole-body exposure to sarin vapor in rats.

Epinephrine-induced arrhythmias (EPIA) are known to be associated with local cardiac cholinergic activation. The present study examined the development of QT prolongation and the effect on EPIA of whole-body exposure of animals to a potent acetylcholine esterase inhibitor. Freely moving rats were exposed to sarin vapor (34.2 +/- 0.8 microg/liter) for 10 min. The electrocardiograms (ECG) of exposed and control animals were monitored every 2 weeks for 6 months. One and six months post exposure, rats were challenged with epinephrine under anesthesia, and the threshold for arrhythmias was determined. Approximately 35% of the intoxicated rats died within 24 h of sarin exposure. Additional occasional deaths were recorded for up to 6 months (final mortality rate of 48%). Surviving rats showed, agitation, aggression, and weight loss compared to non-exposed rats, and about 20% of them experienced sporadic convulsions. Sarin-challenged rats with severe symptoms demonstrated QT segment prolongation during the first 2-3 weeks after exposure. The EPIA that appeared at a significantly lower blood pressure in the treated group in the first month after intoxication lasted for up to 6 months. This decrease in EPIA threshold was blocked by atropine and methyl-atropine. Three months post exposure no significant changes were detected in either k(D) or B(max) values of (3)H-N-methyl scopolamine binding to heart homogenates, or in the affinity of carbamylcholine to cardiac muscarinic receptors. The increase in the vulnerability to develop arrhythmias long after accidental or terror-related organophosphate (OP) intoxication, especially under challenging conditions such as stress or intensive physical exercise, may explain the delayed mortality observed following OP exposure.     

Differential expression of the phthalate syndrome in male Sprague-Dawley and Wistar rats after in utero DEHP exposure

Exposure to phthalate esters during sexual differentiation disrupts testosterone and insulin-like three hormones resulting in malformations of androgen- and insulin-like three-dependent tissues. The current study was designed to test the hypothesis that gubernacular lesions would be more prevalent in the DEHP-treated (750 mg/kg/day, gestational days 14–18) Wistar male than in the SD rat offspring, whereas the SD rat would display a higher incidence of epididymal agenesis. As hypothesized, striking differences were seen in the incidences of epididymal (67% in SD versus 8% in Wistar) and gubernacular lesions (0% in SD versus 64% in Wistar) among the two strains. In addition, fetal androgen and insl3 mRNA levels differed among the strains. SD fetal males had higher insl3 mRNA and lower T levels than Wistar males. The ratio of insl3 mRNA to T differed among DEHP-treated SD and Wistar fetal males, indicating that the steroidogenic pathway was more affected in the SD strain than in the Wistar strain. Taken together, these results suggest that the different malformation profiles produced by in utero phthalate treatment arise, at least in part, from strain differences in fetal Leydig cell function and the manner in which these cells respond to DEHP treatment.