A Dose-Response Analysis of Methoxychlor-Induced Alterations of Reproductive Development and Function in the Rat

A Dose-Response Analysis of Methoxychlor-Induced Alterationsof Reproductive Development and Function in the Rat. GRAY, L.E., JR., OSTBY, J., FERRELL, J., REHNBERG, G., LINDER, R., COOPER,R., GOLDMAN, J., SLOTT, V., AND LASKEY, J. (1989). Fundam. Appl.Toxicol12, 92–108. In the present study rats were dosed fromweaning, through puberty and gestation, to Day 15 of lactationwith methoxychlor at 25, 50, 100, or 200 mg/kg/day. Morphologicallandmarks of puberty were measured, including the ages at vaginalopening, first estrus, and first estrous cycle in females andat preputial separation in males. In the female, estrous cyclicity,fertility, litter size, number of implantation sites, organweights, and ovarian and uterine histology were also measured.The viability of the offspring (F1) and their fertility wereevaluated using a continuous breeding protocol. Males were necropsiedafter breeding, the reproductive organs were weighed, and thecauda epididymal sperm counts were determined. One testis wasused for histopathology, while the other was used to quantifyinterstitial fluid (IF) content, IF testosterone concentration,and testicular sperm production. Testosterone and an drogen-bindingprotein were measured in the caput epididymis, and sperm motilityand morphology were evaluated from a caudal sample. The serumand pituitary were saved for hormonal determinations. Methoxychloraccelerated the age at vaginal opening and first estrus, andthe vaginal smears were cornified. Growth was retarded at 100and 200 mg/kg/day and fertility was reduced when the femaleswere bred with untreated or similarly treated males. In thehighest- dose group, the mated females went from constant estrusinto pseudopregnancy following mating, but they had no implants.In males, methoxychlor treatment markedly reduced growth, seminalvesicle weight, cauda epididymal weight, caudal sperm content,and pituitary weight. Puberty was delayed in the two highest-dosagegroups. Testicular sperm measures were much less affected thancaudal measures. Testis weight and histology were slightly affected,and testicular sperm production, sperm morphology, and motilitywere unaffected. Endocrine function of the testes and pituitarywas altered by methoxychlor administration. Leydig cell testosteroneproduction, in response to human chorionic gonadotropin challenge,was reduced and pituitary levels of prolactin, thyroid-stimulatinghormone (TSH), and follicle-stimulating hormone (FSH) were altered.In contrast, serum levels of prolactin, FSH, and luteinizinghormone were unaffected. Serum TSH was reduced by 50% of controlat 100 and 200 mg/kg/day, while pituitary levels were increased.Gonadotropin-releasing hormone concentration in the mediobasalhypothalamus was also elevated. In spite of the many reproductivealterations, the fertility of treated males was not reducedwhen they were mated with untreated females. Growth and viabilityof the offspring (F1) from the 50 mg/kg/day treatment groupwere normal, but in the females, vaginal opening was accelerated,estrous cyclicity was abnormal in the rats during middle age,and fecundity was reduced.     

Radiological findings in 1135 edentulous patients

A sample consisting of 1135 edentulous patients with clinically healthy denture bearing areas, was examined radiologically. It appears that the diagnostic yield is high whereas the expected radiation induced risk is low. Patients should therefore be examined radiologically prior to full denture construction.     

A Critical Period of Ventricular Fibrillation More Susceptible to Defibrillation: Real-Time Waveform Analysis Using a Single ECG Lead

Previous studies have suggested that variations in the underlying ventricular fibrillation (VF) waveform may be one of the factors responsible for the probabilistic nature of defibrillation. The heart appeared to be more susceptible to defibrillation at higher absolute VF voltages (AVFV). This study investigated in an open-chest canine model (n = 8), a newly developed system that analyzed the VF waveform in real-time, instantaneously determined the time to shock, and immediately delivered a fixed low energy DC shock. A two parameter tracking technique using a running long-term and short-term AVFV average was devised to automatically identify a high voltage peak area of the VF waveform, which has been hypothesized to represent a critical period susceptible to defibrillation. Using a DC shock estimated at the 50% success level, the performance using this technique in 58 defibrillation trials was compared to the performance of the conventional method of shocking at a fixed time (random shock method) in 62 trials. Patch size, electrode location, and discharge voltage were kept constant while VF duration, transmyocardial resistance (TMR), energy delivered, and AVFV at the point of shock were measured. Shock energy and current, TMR, and VF duration were similar with both shock methods. A significantly higher AVFV was observed for trials performed with the peak shock method (0.66 ± 0.02 mV) as compared to trials performed with the random shock method (0.25 ± 0.09 mV) (P < 0.003). Using lead II as the only sensing lead, the success rate was increased in 6 of 8 dogs (75%) with the new method. One animal showed identical performance, and one animal a worse performance. The overall increase in success rate was 24% using a single ECG lead (range 0%-100%; P < 0.04). Our data document that using this algorithm a period of high VF voltage can be detected in realtime. The improved success in the majority of animals supports the hypothesis that a critical period susceptible to defibrillation exists during VF. However, the high AVFV detected using a single ECG lead did not translate to an improved success rate in all animals. This suggests that other factors in addition to the VF voltage measured on a single lead of the ECG are important in characterizing this critical period.     

H-Reflex Waveform and Latency Variability in Rats

H-Reflex Waveform and Latency Variability in Rats. MATTSSON,J. L., ALBEE, R. R., AND BRANDT, L. M. (1984). Fundam. Appl.Toxicol. 4, 944–948. The right tibial nerve of each of11 anesthetized male Fischer 344 rats was electrically stimulatedat the ankle, and H-reflexes were recorded simultaneously fromfour locations in the hind foot. Needle electrodes were usedfor stimulating and recording. The mean (±SD) latencyto the dominant peak of the H reflex was 10.21 ± 0.75msec. Individual rats had a 10% difference in latency from the"fastest" to the "slowest" locations in the foot, although anyof the four locations could produce the fastest (shortest latency)response. The H reflexes varied from simple, single peak waveformsto complex multiple peak waveforms. The dominant peak polaritywas unpredictably either positive or negative. These variationsin complexity and latency occurred among rats and among thefour locations within an individual rat. The dominant peak wasidentified in complex waveforms by adjusting the stimulatingintensity and by recording from more than one location in thefoot. The smallest coefficient of variation (5.57%) resultedfrom selecting data from the fastest electrode locations.     

Neurotoxicity Evaluation of N,N-Diethyl-m-toluamide (DEET) in Rats

The neurotoxic potential of N,N-diethyl-m-toluamide (DEET) wasevaluated following acute oral administration or following multigenerationplus chronic dietary administration to the rat. For the acutestudy, rats were administered undiluted DEET at dose levelsof 50, 200, or 500 mg/kg by gavage. A dose level of 500 mg/kgwas considered to be the highest practical dose that could beevaluated in this study based upon observations of overt toxicityat 500 mg/kg and mortality at 1000 mg/ kg in a dose range-findingstudy. The two measures of neurotoxicity evaluated in the acutestudy were functional observational battery (FOB) and motoractivity measurements. An apparent treatment-related effectin thermal response time (increased) was noted for both sexes1 hr after dosing at the 500 mg/kg dose level. A questionableeffect on rearing activity (decreased) also was noted at thesame dose level. For the multigeneration plus chronic dietaryadministration study, rats were administered DEET at dietaryconcentrations of 0, 500, 2000, or 5000 ppm continuously overtwo generations and then chronically for 9 months. A dietaryconcentration of 5000 ppm meets the criteria for a maximum tolerateddose (MTD) based on traditional chronic toxicology assessments.Evaluations included FOB, motor activity, discriminative acquisitionand reversal in an Mmaze, acoustic startle habituation, passiveavoidance acquisition and retention, and microscopic examinationof central and peripheral nervous tissue. The only effect thatwas considered to be possibly treatment-related was a slightincrease in exploratory locomotor activity at the 5000 ppm doselevel. Based on the results of these studies, the nervous systemdoes not appear to be a selective target when DEET is administeredto rats either as a single oral dose at high dose levels orchronically at the MTD.     

Immunomodulation by Metals

A symposium entitled Immunomodulation by Metals was held atthe 32nd Annual Meeting of the Society of Toxicology (SOT) inNew Orleans, Louisiana. The symposium was cosponsored by theImmunotoxicology and Metals Specialty Sections of SOT and wasdesigned to describe the types of adverse immunological reactionswhich occur in response to environmental and/or occupationalexposure to metals. Epidemiological evidence and underlyingmechanisms responsible for the observed alterations were alsodiscussed. The following is a summary of each of the individualpresentations.     

Acute Spermatogenic Effects of Bromoacetic Acids

Chlorine and bromine can react with natural organic substancesin source waters to form haloacetic acids, major disinfectionby-products of water chlorination. Several toxic effects includingtesticular damage have been attributed to the chloroacetic acidsbut little information is available on the bromine analogues.In this report we present the results of acute toxicity andacute spermatotoxicity studies of monobromoacetic acid (MBAA)and dibromoacetic acid (DBAA). In adult male rats the acuteoral toxicity of MBAA was 10-fold that of DBAA (LD50 177 vs1737 mg/kg). No reproductive-related endpoints were affectedin rats given a single dose of 100 mg MBAA/kg or 14 daily dosesof 25 mg MBAA/kg/day. In rats dosed with DBAA, serum testosteronefell to 17% of control 2 days after a single dose of 1250 mg/kgbut returned to control levels by Day 14. Marked effects onsperm motion were seen on post-treatment Days 14 and 28. Degenerativeflagellar changes in cauda sperm were present on Day 14 whileabnormal sperm head shapes and flagellar degeneration were observedin both caput and cauda sperm on Day 28. Histopathology indicatedaltered spermiation at all timepoints as evidenced by retentionof Step 19 spermatids beyond Stage VIII of the cycle of theseminiferous epithelium. Disorganization, distortion, and degenerationof late spermatids were also observed. On Day 14 structuresresembling residual bodies were rarely seen in the testis butwere numerous in the epididymis. Caput sperm counts were decreased on Day 2 and cauda sperm counts were decreased on Days14 and 28. The data indicate that DBAA is a testicular toxicantin the rat with late and elongating spermatids being particularlysusceptible germinal cells.     

Absorption, Metabolism, and Excretion of N,N-Diethyl-m-toluamide Following Dermal Application to Human Volunteers

The absorption, metabolism, and excretion of N,N-diethyl-m-toluamide(DEET) in male human volunteers following dermal applicationof |¹⁴C|DEET was studied. DEET was applied to two groups ofsix volunteers either as the undiluted technical grade materialor as a 15% solution in ethanol. The material was applied overa 4 x 6-cm area on the volar surface of the forearm and wasleft in contact with the skin for 8 hr, then rinsed off theskin. Application sites also were tape stripped at 1, 23, and45 hr after rinsing. Serial blood samples and all urine andfeces were collected for 5 days after application. Aliquotsof these materials were analyzed for total radioactivity inorder to define absorption and excretion patterns. Urine samplesalso were analyzed by HPLC to characterize the metabolic profileand/or to identify metabolites. Absorption of DEET as evidencedby plasma radioactivity occurred within 2 hr after dose application.Elimination of radioactivity from plasma was rapid and quantifiablelevels of radioactivity were observed in plasma for only 4 hrafter the end of the 8-hr exposure period. Urine was the principalroute of excretion of radioactivity and accounted for an averageof 5.61 and 8.33/ of the applied dose in the undiluted DEETand 15/ DEET in ethanol groups, respectively. Excretion of radioactivityin the feces was less than 0.08/ of the applied dose in bothgroups. DEET did not accumulate in the superficial layers ofthe skin as evidenced by low amounts of radioactivity in thetape strippings. The major fraction of the applied radioactivitywas recovered in the skin rinses. Absorbed DEET was completelymetabolized and six major metabolites were observed in urine.Two major urinary metabolites tenta tively were identified.Based upon the percentage of applied dose recovered in the excreta,dermal absorption of DEET ranged from 3 to 8% with a mean of5.6/ in the volunteers applied undiluted technical grade DEET.The corresponding values for the volunteers applied 15/ DEETin ethanol were 4 to 14/ and 8.4/, respectively.     

The Fungicide Benomyl (Methyl 1 -(Butylcarbamoyl)-2-benzimidazolecarbamate) Causes Testicular Dysfunction by Inducing the Sloughing of Germ Cells and Occlusion of Efferent Ductules

The Fungicide Benomyl (Methyl 1-(Butylcarbamoyl)-2-benzimidazolecarbamate)Causes Testicular Dysfunction by Inducing the Sloughing of GermCells and Occlusion of Efferent Ductules. HESS, R. A., MOORE,B. J., FORRER, J., LINDER, R. E., ABUEL-ATTA, A. A. (1991).Fundam. Appl. Toxicol 17, 733–745. Adult male Sprague-Dawleyrats (100 days of age) were given single oral doses of the fungicidebenomyl (methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate)in dosages ranging from 25 to 800 mg/kg body weight. The testisand excurrent ducts were examined at 2 and 70 days posttreatmentto determine the chemical effects on spermatogenesis and theepididymis. Primary effects seen at 2 days postexposure weretesticular swelling and occlusions of the efferent ductules.Mean testis weight peaked with 400 mg/kg. Premature releaseof germ cells (sloughing), detected even with the lowest dosage(25 mg/kg), was the most sensitive short-term response to benomyl.Sloughing was found primarily in Stage VII of the spermatogeniccycle at the lower dosages, but at higher dosages sloughingextended into all stages except for Stages VIII-XI. Occlusionsof the efferent ductules of the testis were dose-dependent andcorrelated with testis weight. Sperm and sloughed germ cellswere compacted in the ductal lumen of occluded ductules, whichwere surrounded by two to four layers of polymorphonuclear leukocytesand other inflammatory cells. Although the caput epididymidiscontained sloughed germ cells and appeared swollen, evidenceof permanent occlusion was not found. The long-term (70 days)effects of benomyl were decreased testis weight (at 400 mg/kg),dose-dependent increases in seminiferous tubular atrophy, andincreases in the number of reproductive tracts containing occludedefferent ductules. Fibrosis, granulomas, and abnormal growthwere long-term consequences of occluded ductules, which werepresent 100% of the time in testes containing 26–100%seminiferous tubular atrophy. Only a few testes were found tobe completely regressed. Occlusion of efferent ductules anddisruption of the seminiferous epithelium by sloughing of germcells are overlapping dose-dependent mechanisms responsiblefor short- and long-term effects of benomyl on the rat testis.