Comparison of two timed artificial insemination (TAI) protocols for management of first insemination postpartum.

Two estrus-synchronization programs were compared and factors influencing their success over a year were evaluated. All cows received a setup injection of PGF2alpha at 39 +/- 3 d postpartum. Fourteen days later they received GnRH, followed in 7 d by a second injection of PGF2alpha. Cows (n = 523) assigned to treatment 1 (modified targeted breeding) were inseminated based on visual signs of estrus at 24, 48, or 72 h after the second PGF2alpha injection. Any cow not observed in estrus was inseminated at 72 h. Cows (n = 440) assigned to treatment 2 received a second GnRH injection 48 h after the second PGF2alpha, and all were inseminated 24 h later. Treatment, season of calving, multiple birth, estrual status at insemination, number of occurrences of estrus before second PGF2alpha, prophylactic use of PGF2alpha, retained fetal membranes, and occurrence of estrus following the setup PGF2alpha influenced success. Conception rate was 31.2% (treatment 1) and 29.1% (treatment 2). A significant interaction occurred between protocol and estrual status at insemination. Cows in estrus at insemination had a 45.8% (treatment 1) or 35.4% (treatment 2) conception rate. The conception rate for cows not expressing estrus at insemination was 19.2% (treatment 1) and 27.7% (treatment 2). Provided good estrous detection exists, modified targeted breeding can be as successful as other timed artificial insemination programs. Nutritional, environmental, and management strategies to reduce postpartum disorders and to minimize the duration of postpartum anestrus are critical if synchronization schemes are used to program first insemination after the voluntary waiting period.

Evaluation of spinosad in a two-generation dietary reproduction study using Sprague-Dawley rats.

Spinosad, an insecticide derived from a naturally occurring bacterium via fermentation, represents a new class of insecticides acting by a novel mode of action. A dietary study was conducted in Sprague-Dawley rats in which groups of 30 rats/sex/dosage level were given diets that provided 0, 3, 10, or 100 mg spinosad/kg body weight/day, 7 days/week, for 2 successive generations. Following 10 weeks of dietary exposure, the P1 generation was mated twice to produce F1a and F1b litters. After weaning, groups of 30 rats/sex/dosage level were selected from the F1a litters, given diets containing spinosad for 12 weeks, and mated to produce the F2 generation. Dietary administration of spinosad to rats at a dosage of 100 mg/kg/day over 2 generations produced parental toxicity and effects on the offspring. Among adult males, body weights and weight gains were decreased 2-9% relative to controls, with P1 males more affected than P2. Absolute and relative liver, kidney, heart, spleen, and thyroid weights were increased by from 12% to as much as 240% of control values. Histologic changes consistent with cationic amphiphilic compounds were noted in the kidneys, lungs, mesenteric lymph nodes, spleen, and thyroid of P1 and P2 males and females. In females given 100 mg/kg/day, though premating body weights were not affected, weight gains during the F1a and F1b gestation periods were depressed 15-16%. Increased incidences of dystocia, and vaginal bleeding and mortality occurred during parturition and lactation at 100 mg/kg/day. Effects on the offspring (decreased litter size and survival through day 4 of lactation) were limited to the high-dosage group. Signs indicative of poor maternal care noted in the pups (stomachs void of milk, cold, thin, etc.) were observed at 100 mg/kg/day. Early postnatal effects on the offspring were considered likely secondary to the effects in maternal animals around the time of parturition. At 100 mg/kg/day, weight gain in pups was depressed throughout lactation, with statistically significantly decreased weights noted toward the latter half of the lactation period. There were no treatment-related effects on adults or their offspring at 3 or 10 mg/kg/day in either generation. Based on these results, spinosad is not considered a selective reproductive toxicant, (i.e., no effects on reproductive parameters were noted below a level that produced toxicity in the adults) and the no observed effect level (NOEL) for both parental and reproductive/perinatal toxicity was 10 mg/kg/day.

Effects of teatcup liner tension on teat canal keratin and teat condition in cows.

The effect of tension of teatcup liners on teat end condition and quantity of keratin in the teat canal was investigated. Liner tension was increased by using longer teatcup shells. The first experiment used six Holstein cows in early lactation. Left quarters were milked with liners under medium or normal tension by using Conewango liners in 142 mm shells. Right quarters were milked with liners under high tension by mounting the liners in teatcup shells 149 mm in length. By day 16 teat end condition and sensitivity to manipulation were worsened by thrice daily milking when liners were under a higher tension. Two subsequent experiments each used 12 different Holstein cows. These cows were in mid lactation and were milked twice daily for 10 or 30 d. Left quarters were milked with liners under high tension Right quarters were milked with liners under low tension by using teatcup shells 126 mm in length. The quantity of keratin removed during milking was not influenced by liner tension: however, the quantity of keratin at the end of the experiments was increased 10-20% in teats that were milked using liners under higher tension. Histological analysis and keratin content were consistent with epithelial hyperplasia induced by milking with liners under increased tension.

Identification of RIP3, a RIP-like kinase that activates apoptosis and NFkappaB.

The tumor necrosis factor receptor 1 (TNFR1) and the Fas receptor recruit complexes formed by the interactions between RIP kinase, TRADD, FADD and RAIDD - adaptor proteins that contain death domains - which in turn recruit other proteins to initiate signaling [1][2][3][4][5]. To identify proteins associated with the TNF signaling pathway, we performed a yeast two-hybrid interaction screen using RIP as bait. We isolated a kinase, RIP3, which shares homology with the kinase domain of RIP and RIP2 (also known as Rick or CARDIAK). RIP3 could be co-immunoprecipitated with RIP, TRAF2 and TNFR1 in mammalian cells. The carboxy-terminal domain of RIP3, like that of RIP, could activate the transcription factor NFkappaB and induce apoptosis when expressed in mammalian cells. Interestingly, this region shares no significant sequence homology to the death domain of RIP, the caspase-recruiting domain (CARD) of RIP2 [6][7][8] or any other apoptosis-inducing domain. As with RIP and RIP2, the kinase domain of RIP3 was not required for either NFkappaB activation or apoptosis induction. Overexpression of a dominant-negative mutant of RIP3 strongly inhibited the caspase activation but not the NFkappaB activation induced by TNFalpha. Therefore, RIP3 appears to function as an intermediary in TNFalpha-induced apoptosis.

Subchronic and chronic toxicity of ingested 1,3-dichloropropene in dogs.

The potential toxicologic effects to dogs of 1,3-dichloropropene (1, 3-D), a soil fumigant used for the control of nematodes, were investigated. The 13-week subchronic toxicity study consisted of male and female beagle dogs (4/sex/dose group) given approximately 0, 5, 15, or 41 mg 1,3-D/kg body wt/day (approximately equivalent amounts of cis and trans isomers) via their diets. The 1-year chronic toxicity study consisted of male and female beagle dogs (4/sex/dose group) provided diets delivering approximately 0, 0.5, 2. 5, or 15 mg/kg body wt/day. The test material was stabilized in the feed by microencapsulation in a starch/sucrose matrix (80/20). In both the 13-week and the 1-year studies, the primary effect of 1,3-D in male and female dogs ingesting a dosage of >/=15 mg/kg/day was hypochromic, microcytic anemia. The anemia was regenerative, with increased erythropoietic activity characterized by polychromasia of erythrocytes and increased numbers of reticulocytes in peripheral blood. In the 13-week study, the anemia in dogs given 41 mg/kg/day progressively worsened over time, while the anemia in dogs given 15 mg/kg/day remained relatively constant between 42 and 90 days of dosing. Partial reversal of the anemia of high-dose animals occurred during a 5-week recovery period following the 13-week dosing regimen. In the 13-week study, terminal fasted body weights of males given 15 or 41 mg/kg/day were decreased 3 and 28%, respectively, and body weights of females given 5, 15, or 41 mg/kg/day were decreased 4.5, 12, and 24%, respectively, relative to controls. Males given 5 mg/kg/day for 13 weeks had no change in body weights relative to controls. In the 1-year study, the hypochromic microcytic anemia in dogs given 15 mg/kg/day remained relatively constant in severity between 3 and 12 months of treatment. Histopathologic alterations associated with anemia in the 1-year study consisted of increased hematopoiesis of the bone marrow and increased extramedullary hematopoiesis of the spleen. Body weights of males given 15 mg/kg/day were 5-12% lower than controls during the first 13 weeks of the study and 13-19% lower than controls during the remaining 9 months. Body weights of females given 15 mg/kg/day were 5-14% lower than controls over the majority of the dosing period. Males and females given 0.5 or 2.5 mg/kg/day for 1 year had no change in body weights relative to controls. A no-observed-effect level of 2.5 mg/kg/day was established for male and female dogs from the 1-year study.

Evaluation of renal function in rhesus monkeys and comparison to beagle dogs following oral administration of the organic acid triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid).

The current study evaluated the effects of triclopyr (3,5, 6-trichloro-2-pyridinyloxyacetic acid) on renal function following oral administration in the beagle dog and rhesus monkey. Male rhesus monkeys were orally administered triclopyr by gavage at a dose of 5 mg/kg/day, 7 days/week for 28 days, after which the dosage was increased to 20 mg/kg/day for 102 consecutive days. Groups of male dogs were administered either a single oral dose of 5 mg/kg triclopyr or were fed a diet spiked with triclopyr at a dose of 5 mg/kg/day for 47 consecutive days. The following functional and clinical chemistry parameters were evaluated: exogenous phenolsulfonphthalein (PSP) excretion, inulin and para-aminohippurate (PAH) clearance (monkeys only), endogenous serum creatinine, and blood urea nitrogen (BUN) at multiple time points during the study. Creatinine, BUN, and inulin clearance were within the normal range from both species following triclopyr administration which indicates that repeated administration of triclopyr in the dog and monkey had no effect on glomerular filtration rate (GFR). In monkeys, the percentage excretion of PSP and PAH appeared to increase following triclopyr administration (20 mg/kg/day), suggesting that these weak organic acids may be competing for the same plasma protein-binding site enhancing their clearance. More importantly, these data strongly suggest that triclopyr is not competing with PSP or PAH for the active secretory site within the monkey kidney proximal tubules. In contrast, PSP clearance studies in dogs clearly demonstrated that triclopyr administration (5 mg/kg) can significantly decrease the percentage PSP excretion even following a single dose administration. The decrease in percentage PSP was reversible and inversely related to the plasma triclopyr concentration. Overall, these data clearly indicate that triclopyr effectively competes with PSP for the active secretory site within the dog kidney proximal tubules. In contrast, the monkey was insensitive to the effects of triclopyr on the active secretory process even at doses fourfold higher (20 mg/kg/day) than the effective dose in the dog (5 mg/kg/day). These findings suggest that the effect observed on PSP and PAH excretion in the dog represent a physiological competition for excretion and not toxicity.

Evaluation of the developmental and reproductive toxicity of chlorpyrifos in the rat.

Chlorpyrifos (O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)-phosphorothioate), an organophosphate insecticide, was evaluated for its potential to produce developmental and reproductive toxicity in rats following oral exposure. Pregnant Fischer 344 rats were given doses of 0 (corn oil vehicle), 0.1, 3.0, or 15 mg chlorpyrifos/kg/day, by gavage, on Gestation Days 6 through 15. Maternal effects noted at the two higher dose levels included decreased cholinesterase levels at 3.0 mg/kg/day and cholinergic signs (excessive salivation and tremors), decreased cholinesterase levels, and decreased body weight gain at 15 mg/kg/day. No maternal effects were apparent at 0.1 mg/kg/day. Although maternal toxicity was observed at these two higher exposure levels, no developmental effects were noted at any dose. In a two-generation reproduction study, Sprague-Dawley rats were maintained on diets supplying 0, 0.1, 1.0, or 5.0 mg chlorpyrifos/kg/day. Parental effects included decreased plasma and erythrocyte cholinesterase at 1.0 mg/kg/day, and decreased plasma, erythrocyte, and brain cholinesterase and histopathologic alterations of the adrenal zona fasciculata at 5.0 mg/kg/day. The histopathologic alterations of the adrenal were characterized as very slight to slight vacuolation (consistent with fatty change) in males, and very slight vacuolation and/or altered tinctorial properties in females. No effects on the reproductive or fertility indices or on the histopathology of reproductive tissues were observed at any dose level, and no neonatal effects were observed at 0.1 or 1.0 mg/kg/day in the F1 or F2 litters. Parental toxicity at the high dose was accompanied by decreased pup body weight and increased pup mortality in the F1 litters only. These data show that oral administration of chlorpyrifos to rats at parentally toxic dose levels was not embryolethal, embryo/fetotoxic, or teratogenic and did not adversely affect fertility or the function or structure of the reproductive organs. Although effects on neonatal growth and survival were observed at a maternally toxic dose level in one generation, this effect was not observed in the subsequent generation and, therefore, may not have been related to treatment.

Postural effects on intra-abdominal pressure during Valsalva maneuver.

When lifting heavy loads, trunk muscle contraction converts the abdominal and thoracic cavities into a nearly rigid-walled cylinder that provides increased extrinsic stability and allows partial transfer of load away from the spine. Because twisting is a common mechanism of low-back injuries, this study was undertaken to determine if trunk rotation results in a decrease in the extrinsic stability of the spine. We studied the effects of changes in trunk posture on intra-abdominal pressure generated during a maximum effort Valsalva's maneuver (IAP max) in eight healthy volunteers. IAP max during standing combined with trunk rotation was found to be significantly lower than IAP max during standing straight (p < 0.05). IAP max during forward flexion combined with trunk rotation was significantly lower than during forward flexion (p < 0.01). The results of our study indicate that trunk rotation adversely effects the ability to perform a Valsalva's maneuver. We conclude that extrinsic stability of the spine is at a biomechanical disadvantage when the trunk is rotated and thus may be a contributing factor to twisting-type back injuries.

In vitro kinetics of styrene and styrene oxide metabolism in rat, mouse, and human.

Styrene oxide (SO), a labile metabolite of styrene, is generally accepted as being responsible for any genotoxicity associated with styrene. To better define the hazard associated with styrene, the activity of the enzymes involved in the formation (monooxygenase) and destruction of SO (epoxide hydrolase and glutathione-S-transferase) were measured in the liver and lungs from naive and styrene-exposed male Sprague-Dawley rats and B6C3F1 mice (three daily 6-h inhalation exposures at up to 600 ppm styrene) and Fischer 344 rats (four daily 6-h inhalation exposures at up to 1000 ppm styrene), and in samples of human liver tissue. Additionally, the time course of styrene and SO in the blood was measured following oral administration of 500 mg styrene/kg body weight to naive Fischer rats and rats previously exposed to 1000 ppm styrene. The affinity of hepatic monooxygenase for styrene, as measured by the Michaelis constant (Km), was similar in the rat, mouse, and human. Based on the Vmax for monooxygenase activity and the relative liver and body size, the mouse had the greatest capacity and humans the lowest capacity to form SO from styrene. In contrast, human epoxide hydrolase and a greater affinity (i.e., lower Km) for SO than epoxide hydrolase from rats or mice while the apparent Vmax for epoxide hydrolase was similar in the rat, mouse, and human liver. However, the activity of epoxide hydrolase relative to monooxygenase activity was much greater in the human than in the rodent liver. Hepatic glutathione-S-transferase activity, as indicated by the Vmax, was 6- to 33-fold higher than epoxide hydrolase activity. However, the significance of the high glutathione-S-transferase activity is unknown because hydrolysis, rather than conjugation, is the primary pathway for SO detoxification in vivo. Human hepatic glutathione-S-transferase activity was extremely variable between individual human livers and much lower than in rat or mouse liver. Prior exposure to styrene had no effect on monooxygenase activity or on blood styrene levels in rats given a large oral dose of styrene. In contrast, prior exposure to styrene increased hepatic epoxide hydrolase activity 1.6-fold and resulted in lower (0.1 > P > 0.05) blood SO levels in rats given a large oral dose of styrene. Qualitatively, these data indicate that the mouse has the greatest capacity and the human the lowest capacity to form SO. In addition, human liver should be more effective than rodent liver in hydrolyzing low levels of SO.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimating the risk of liver cancer associated with human exposures to chloroform using physiologically based pharmacokinetic modeling.

A physiologically based pharmacokinetic (PB-PK) model for CHCl3 has been used to prepare estimates of the probability that human populations exposed to low levels of CHCl3 will develop liver tumors similar to those seen in rodent bioassays. The PB-PK model for CHCl3 was based on a model reported earlier by Corley et al. (1990), but this model differed from that of Corley et al. in that it was also capable of describing a pharmacodynamic endpoint: induction of cytotoxicity in the liver of CHCl3-exposed animals produced by reactive metabolites of CHCl3. Pharmacodynamic descriptions in this model were derived from experimental measurements of cell replication ([3H]thymidine incorporation) as well as from quantitative histopathology in the liver of rats and mice. Two different approaches were used for hazard evaluation: (1) a "Safety Factor" approach based on no observed effect levels for liver tumors. and (2) calculation of lower confidence limits on risk-specific doses with the GLOBAL83 computer program. In each case, cytotoxicity produced by reactive CHCl3 metabolites was used as the measure of "dose" to the liver. The Safety Factor approach suggested that continuous exposure of human populations to concentrations of CHCl3 less than 2840 ppb in air or 13,900 ppb in water would not be likely to significantly increase the risk of developing liver tumors. The second approach suggested a "plausible upper 95% confidence limit" of 1 x 10(-5) for lifetime excess cancer risk for human populations continuously exposed to 2200 or 13,100 ppb CHCl3 in air or water, respectively.

The chronic toxicity and oncogenicity of inhaled technical-grade 1,3-dichloropropene in rats and mice.

Male and female Fischer 344 rats and B6C3F1 mice were exposed by inhalation to target concentrations of 0, 5, 20, or 60 ppm (0, 22.7, 90.8, or 272 mg/m3) technical-grade 1,3-dichloropropene (DCPT) 6 hr/day, 5 days/week, for up to 2 years. Ancillary groups of rats and mice were exposed for 6- and 12-month periods. Significant treatment-related nonneoplastic changes following exposure for 2 years were morphological alterations in the nasal tissues of rats exposed to 60 ppm and mice exposed to 20 or 60 ppm DCPT. In addition, mice exposed to 20 or 60 ppm had hyperplasia of the transitional epithelium lining the urinary bladder. Survival of male and female rats and mice exposed to DCPT was similar to that of the corresponding controls. No statistically increased tumor incidence was observed in treated rats. The only neoplastic response observed in mice was an increased incidence of benign lung tumors (bronchioloalveolar adenomas) in male mice exposed to 60 ppm DCPT (22/50 versus 9/50 in controls).

1,3-dichloropropene: two-generation inhalation reproduction study in Fischer 344 rats.

This study evaluated the effects of inhaled technical-grade 1,3-dichloropropene (DCPT) on reproduction and neonatal growth and survival. Groups of 30 male and 30 female Fischer 344 rats, approximately 6 weeks of age, were exposed via inhalation to 0, 10, 30 or 90 ppm DCPT for 6 hr/day, 5 days/week, for two generations. The parental f0 and f1 generations were each bred twice. Reproductive and neonatal parameters evaluated included indices of fertility and pup survival, gestation length, litter size, pup body weight, and pup sex ratio. Gross and histologic examinations were concluded on all f0 and f1 adults. In addition, randomly selected f1b and f2b weanlings were given gross examinations. Parental effects were limited to rats exposed to 90 ppm DCPT and included decreased body weights and histopathologic effects on the nasal mucosa of adult male and female rats. The histopathologic effects consisted of slight, focal hyperplasia of the respiratory epithelium and/or focal degenerative changes in the olfactory epithelium. No adverse effects on reproductive parameters or neonatal growth or survival were observed in the f1a, f1b, f2a, or f2b litters even at an exposure concentration which produced effects in adult animals. Based on these results, it is concluded that inhalation exposure of rats up to 90 ppm DCPT for two successive generations did not adversely affect the reproductive and neonatal parameters evaluated.

1,1,1-trichloroethane formulation: a chronic inhalation toxicity and oncogenicity study in Fischer 344 rats and B6c3F1 mice.

Groups of male and female Fischer 344 rats and B6C3F1 mice (80/sex/group) were exposed to vapor concentrations of 0, 150, 500, or 1500 ppm 1,1,1-trichloroethane formulation 6 hr/day, 5 days/week, for 2 years. Ten rats and mice/sex from each group were predesignated for interim sacrifices after 6, 12, and 18 months of exposure. Fifty rats and mice/sex/group were assigned to the study to be terminated after 24 months. Parameters measured during the study included mortality, in-life clinical signs of toxicity, hematology, urinalysis (rats only), clinical chemistry, body weight, organ weights (liver, kidneys, brain, heart, testes), gross pathology, and histopathology. Inhalation exposure of male and female Fischer 344 rats to 1500 ppm vapor of the 1,1,1-trichloroethane formulation for 2 years resulted in a significant decrease in body weights of females. In addition, very slight microscopic hepatic effects were seen in the liver of 1500 ppm-exposed male and female rats necropsied at 6, 12, and 18 months. The hepatic effects could not be discerned at 24 months due to confounding geriatric changes. In the rats exposed to 150 and 500 ppm there were no changes that were considered due to exposure to the 1,1,1-trichloroethane formulation. There were no toxic effects noted in male or female mice at any exposure concentration tested. There were no indications of an oncogenic effect in rats or mice following 2 years of exposure to this 1,1,1-trichloroethane formulation.

Teratologic evaluation of 2-phenoxyethanol in New Zealand White rabbits following dermal exposure.

2-Phenoxyethanol was applied to the clipped skin of pregnant rabbits on Days 6 through 18 of gestation in order to assess the fetotoxic and teratogenic potential by the dermal route. Rabbits were treated with 0, 300, 600, or 1000 mg/kg/day of 2-phenoxyethanol, and fetuses were examined for external, visceral, and skeletal alterations. Dermal application of 1000 mg/kg/day produced maternal toxicity as evidenced by intravascular hemolysis of red blood cells and death in some animals. Maternal toxicity was observed in rabbits treated with 600 mg 2-phenoxyethanol/kg/day but at a lower incidence than that observed at 1000 mg/kg/day. Nine rabbits in the 1000 mg/kg/day dose group and five rabbits at 600 mg/kg/day died or were sacrificed in extremis. Rabbits in the two highest dose groups which survived until Day 28 of gestation showed no evidence of treatment-related effects. No signs of maternal toxicity were seen at 300 mg/kg/day. Examination of rabbit fetuses indicated that, at the dosages tested, 2-phenoxyethanol was not embryotoxic, fetotoxic, or teratogenic.

Teratologic evaluation of dermally applied diethylene glycol monomethyl ether in rabbits.

Diethylene glycol monomethyl ether (DEGME) was applied to the skin of pregnant rabbits on Days 6 through 18 of gestation in order to assess the fetotoxic and teratogenic potential by the dermal route. Rabbits were treated with 0, 50, 250, or 750 mg/kg/day of DEGME, and fetuses were examined for external, visceral, and skeletal alterations. Topical application of the highest dose, 750 mg/kg/day, produced slight embryotoxicity, fetotoxicity, and toxicity in the maternal animal. Maternal effects were characterized by decreased weight gain and a concurrent physiologic decrease in red blood cells and packed cell volume values. In addition, a slight increase in embryonic resorptions was observed. The fetal alterations observed, mild forelimb flexure, slight-to-moderate dilation of the renal pelvis, retrocaval ureter, cervical spurs, and delayed ossification of the skull and sternebral bones, are considered to be indicative of fetotoxicity but not teratogenicity. Slight fetotoxicity in the form of delayed ossification of the skull and cervical spurs was seen in the 250 mg/kg/day dose group. No adverse maternal, embryonic, or fetal effects were observed at 50 mg/kg/day.

Neurotoxicologic examination of rats dermally exposed to 2,4-D amine for three weeks.

There was no evidence of peripheral neuropathy or other neurotoxicity in rats dermally treated with a 12% aqueous solution of the amine salt of 2,4-dichlorophenoxyacetic acid (2,4-D amine). Male and female Fischer 344 rats were treated on the skin of all four limbs with 2,4-D amine for 2 hr/day, 5 days/week, for 3 weeks. Measurements were: body weights, hindlimb grip strength, accelerating rod performance, single and paired pulse electrophysiology of the caudal and sciatic nerves, hindfoot H-reflexes, light microscopy of brain, spinal cord, sciatic nerve, tibial nerve, digital nerve, and electron microscopy of the tibial nerve. The experiment continued for up to one month postexposure. Treatment caused a weight loss in both male and female rats and caused minor skin changes during treatment in both sexes. No other treatment-related effects were found.

Chronic toxicity and oncogenicity study on inhaled vinylidene chloride in rats.

Male and female Sprague-Dawley rats (Spartan substrain) were exposed to vinylidene chloride (VDC) by inhalation for 18 months to assess chronic toxicity and oncogenic potential of the subject test material. Interim sacrifices were performed at 1, 6, and 12 months. Rats were exposed to VDC concentrations of 10 and 40 ppm for 6 hr/day, 5 days/week for the first 5 weeks of the study. Based upon the absence of observable treatment-related effects among rats sacrificed after 1 month of exposure, the exposure concentrations were increased to 25 and 75 ppm VDC. Exposures were continued at these concentrations through the 18th month of the study after which the surviving animals were held until 24 months and then sacrificed. Cytogenetic evaluations were performed on a separate group of animals, four rats/sex, exposed to 0, 25, or 75 ppm VDC for 6 months. There were no exposure-related changes in the following parameters: mortality, appearance and demeanor, body weight data, clinical chemistry determinations, hematologic evaluations, urinalysis, or cytogenetic evaluation of bone marrow preparations. A target organ effect, characterized by hepatocellular fatty change in the midzonal region of the hepatic lobule which was minimal in severity, was observed in both male and female rats of both the 25- and 75-ppm exposure groups as early as the 6-month interim sacrifice. The midzonal fatty change was also observed at the 12-month sacrifice but no indication of progression of this lesion in either severity or incidence was apparent. During the last 6 months of the study, after exposures had been discontinued, this effect was no longer discernible; therefore this alteration was readily reversible. The incidences of several tumors and/or tumor types were statistically increased or decreased in VDC-exposed rats when compared to their respective control groups; none of these differences were judged to be attributable to VDC exposure.

Neurotoxicity of methyl chloride in continuously versus intermittently exposed female C57BL/6 mice.

This study evaluated the relationship between methyl chloride (MeCl) exposure duration and neurotoxicity. Female C57BL/6 mice were exposed to MeCl for 11 days, either continuously (22 hr/day) to 15, 50, 100, 150, or 200 ppm, or intermittently (5.5 hr/day) to 150, 400, 800, 1600, or 2400 ppm. This strain and sex of mouse was chosen because it is sensitive to MeCl neurotoxicity and was a good candidate to allow the evaluation of morphological effects and the quantitation of functional effects. A simple quantitative relationship between neurotoxicity and continuous vs intermittent exposure was not observed. Although the no-observable-effect levels for continuous and intermittent MeCl exposures were very nearly proportionate to exposure concentration multiplied by duration, the dose-response curve was much steeper for continuously exposed mice. Cerebellar granular cell layer degeneration was observed in mice exposed continuously to 100 ppm MeCl and in mice exposed intermittently to 400 ppm. This histopathologic effect was observed at lower concentrations than a decrement in rotating rod running performance. No effects were observed in mice exposed to 50 ppm continuously or to 150 ppm intermittently. Continuous exposure to MeCl produced the cerebellar lesion with less effect on other tissues than did intermittent exposure. In mice exposed to 2400 ppm intermittently, there were renal and hematopoietic effects in addition to relatively slight cerebellar granular cell layer degeneration. These 2400-ppm exposed mice developed hemoglobinuria, apparently as a result of intravascular hemolysis. Although the effect of exposure duration on MeCl toxicity was complex, this study indicated that careful judgment is necessary when extrapolating intermittent exposure data to a continuous exposure situation.