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.

Developmental toxicity studies in rats and rabbits on 2,4-dichlorophenoxyacetic acid and its forms.

The potential for 2,4-D and its salts and esters to induce developmental toxicity was investigated in rats (8 studies) and rabbits (7 studies). Maternal toxicity associated with exposure was dependent on the dose level expressed as 2,4-D acid equivalents. The severity of the maternal effect was correlated to the 2,4-D acid-equivalent dose, with increasing dose levels that exceeded renal clearance causing increasingly more severe maternal effects. In both species, maternal body weight effects began to be manifested at dose levels of 30 mg 2,4-D acid equivalent/kg/day. At higher dose levels (50-75 mg/kg/day in rats and 75-90 mg/kg/day in rabbits), body weights and feed consumption were more severely affected. At dose levels > or =90 mg/kg/day in rats, clinical signs of toxicity (ataxia, muscular stiffness, and decreased motor activity) and mortality were noted. The no-observed-adverse-effect level (NOAEL) for maternal toxicity in both species across the family of 2,4-D salts and esters was approximately 10 mg/kg/day. Significantly decreased fetal body weights and increased fetal variations were seen in rats only at maternally toxic dose levels in excess of 90 mg/kg/day acid equivalent. At maternally toxic doses in rabbits, embryonal and fetal development were essentially unaffected. There were no effect on maternal reproductive measures such as litter size, resorption rates, or fetal body weights, and there was no evidence of teratogenic activity. In summary, equivalent toxicity of the salts and esters is consistent with rapid and complete metabolic conversion to 2,4-D acid. No adverse fetal effects were noted at dose levels that did not also produce evidence of maternal toxicity or exceed renal clearance of 2,4-D indicating that the developing rat and rabbit fetus were not uniquely sensitive to 2,4-D and its forms.

Lack of selective developmental neurotoxicity in rat pups from dams treated by gavage with chlorpyrifos.

Pregnant Sprague-Dawley rats were given chlorpyrifos (O:, O-diethyl-O:-[3,5,6-trichloro-2-pyridinyl] phosphorothioate; CPF) in corn oil by gavage from gestation day 6 (GD 6) through lactation day 10 (LD 10) at dosages of 0, 0.3, 1, or 5 mg/kg/day in a developmental neurotoxicity study that conformed to U.S. Environmental Protection Agency 1991 guidelines. GD 0 was the day when evidence of mating was observed and postnatal day 0 (PND 0) was the day of birth. Toxicity was limited to the highest dosage level (5 mg/kg/day) and, in the dams, consisted of muscle fasciculation, hyperpnea, and hyperreactivity. A nonsignificant overall trend toward weight gain and feed consumption was also observed in the high-dosage dams, with a statistically significant Group x Time interaction for reduced weight gain in the 5-mg/kg/day group near the end of gestation. Although many developmental indices were normal, pups from high-dosage dams had increased mortality soon after birth, gained weight more slowly than controls, and had several indications of slightly delayed maturation. The early deaths and delayed maturation were attributed to maternal toxicity, though a possible contributing role of direct pup toxicity in delayed development cannot be eliminated. In spite of the apparent delay in physical development, high-dosage pups tested just after weaning had normal learning and memory as tested on a T-maze spatial delayed-alternation task. Habituation, a primitive form of learning, was tested in 2 tasks (motor activity and auditory startle) and was not affected. No overt effects were noted in either dams or pups at 1 or 0.3 mg/kg/day. Based on these data, chlorpyrifos produced maternal and developmental toxicity in the 5-mg/kg/day-dosage group. There was no evidence of selective developmental neurotoxicity following exposure to chlorpyrifos.

Developmental toxicity studies in rats and rabbits with 3,5,6-trichloro-2-pyridinol, the major metabolite of chlorpyrifos.

3,5,6-Trichloro-2-pyridinol (TCP), the primary metabolite of chlorpyrifos and chlorpyrifos-methyl, was evaluated for potential developmental toxicity. Groups of 32-34 bred female Fischer 344 rats were given 0, 50, 100, or 150 mg TCP/kg/day by gavage on gestation days 6-15; the fetuses were evaluated on gestation day 21. Similarly, groups of 16 inseminated female New Zealand White rabbits were given 0, 25, 100, or 250 mg TCP/kg/day by gavage on gestation days 7-19, and fetuses were evaluated on gestation day 28. No clinical signs of toxicity attributed to TCP were noted in either species. In rats, at 150 mg/kg/day, maternal effects included slight decreases in feed consumption, significantly depressed body weight gain (25% relative to controls) resulting in significantly lower maternal terminal body weights, and increased relative liver weight. At 100 mg/kg/day, maternal body weight gain in rats was depressed approximately 22%. Among rabbits, maternal effects were limited to the group given 250 mg/kg/day, which lost an average of approximately 70 g during the treatment period (vs. 140 g in the controls). There were no effects on fetal weight or viability, nor were there significant increases in any fetal alteration in either species. A slightly higher (not statistically significant) than usual incidence of central nervous system anomalies occurred in rabbits, but these anomalies were found in both treated and control groups in this study as well as contemporaneous studies of unrelated compounds. This, and the fact that these anomalies were not seen with the parent compound, chlorpyrifos, suggest that their origin was spontaneous. Thus, TCP was not considered fetotoxic or teratogenic in either rats or rabbits, even at dose levels that produced maternal toxicity.

Separation optimization for the recovery of phenyl ethyl alcohol.

Phenyl ethyl alcohol is a compound that occurs naturally in flower petals and in many common beverages, such as beer. Desire for the floral, rose-like notes imparted by phenyl ethyl alcohol has created a unique niche for this chemical in flavor and fragrance industries. Phenyl ethyl alcohol can be produced by Saccharomyces cerevisiae via bioconversion. Often this method of production results in extremely low yields, thus placing a great deal of importance on recovery and purification of the valuable metabolite. To determine the best method for recovering the chemical, a primary recovery step and a secondary recovery step were developed. The primary recovery step consisted of comparing dead-end filtration with crossflow ultrafiltration. Crossflow ultrafiltration was ultimately selected to filter the fermentation broth because of its high flow rates and low affinity for the product. The secondary recovery step consisted of a comparison of liquid- liquid extraction and hydrophobic resin recovery. The hydrophobic resin was selected because of its higher rate of recovery and a higher purity than the liquid-liquid extraction, the current practice of Brown-Forman.

Improved oxygen delivery in a continuous-roller-bottle reactor.

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k(L)a values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.

Effect of impeller geometry on gas-liquid mass transfer coefficients in filamentous suspensions.

Volumetric gas-liquid mass transfer coefficients were measured in suspensions of cellulose fibers with concentrations ranging from 0 to 20 g/L. The mass transfer coefficients were measured using the dynamic method. Results are presented for three different combinations of impellers at a variety of gassing rates and agitation speeds. Rheological properties of the cellulose fibers were also measured using the impeller viscometer method. Tests were conducted in a 20 L stirred-tank fermentor and in 65 L tank with a height to diameter ratio of 3:1. Power consumption was measured in both vessels. At low agitation rates, two Rushton turbines gave 20% better performance than the Rushton and hydrofoil combination and 40% better performance than the Rushton and propeller combination for oxygen transfer. At higher agitation rates, the Rushton and hydrofoil combination gave 14 and 25% better performance for oxygen transfer than two Rushton turbines and the Rushton and hydrofoil combination, respectively.

Measurement of the steady-state shear characteristics of filamentous suspensions using turbine, vane, and helical impellers.

The impeller viscometer technique is frequently used to characterize the rheology of filamentous suspensions in order to avoid difficulties encountered with conventional instruments. This work presents the results of experiments conducted with vane, turbine, and helical impellers. The validity of the assumptions made in the determination of the torque and shear-rate constants were assessed for each impeller type. For the turbine and vane impellers, an increase in the apparent torque constant c was observed with increasing Reynolds number even when measurements were confined to the viscous regime. The shear-rate constants determined for the vane and turbine impellers varied for different calibration fluids, which contradicts the assumptions usually invoked in the analysis of data for this technique. When the helical impeller was calibrated, consistent values for the torque and shear-rate constants were obtained. The three impeller types were also used to characterize the rheology of cellulose fiber suspensions and the results compared for consistency and reproducibility. The results have application in design of rheometers for use in process control and product quality assessment in the fermentation and pulp and paper industries.

Developmental toxicity of 1,2-dichloropropane (PDC) in rats and rabbits following oral gavage.

1,2-Dichloropropane (PDC) was evaluated for its potential to cause embryonal/fetal toxicity and teratogenicity in pregnant rats and rabbits. PDC was administered via oral gavage at dose levels of 0, 10, 30, or 125 mg/kg/day on Days 6 through 15 of gestation (rats) or 0, 15, 50, or 150 mg/kg/day on gestation Days 7 through 19 (rabbits). Fetuses were examined on Gestation Day 20 (rats) or Day 28 (rabbits). Maternal toxicity was observed in both rats and rabbits at the high dose levels. Rats given 125 mg/kg/day of PDC showed clinical signs of toxicity and decreased body weight and body weight gain. Rabbits given 150 mg/kg/day PDC showed changes in hematologic parameters and decreased body weight gain. Although maternal toxicity was apparent, no indication of teratogenicity was observed in rat or rabbit fetuses at any dose level. Significant increases in the incidence of delayed ossification of skull bones, considered secondary to decreased maternal body weight gain, were observed in rats given 125 mg/kg/day and in rabbits given 150 mg/kg/day. No maternal or developmental effects were observed in rats given 10 or 30 mg/kg/day or in rabbits given 15 or 50 mg/kg/day of PDC. Based on the results of these studies the maternal and developmental NOELs in rats and rabbits were 30 and 50 mg/kg/day, respectively.

Metabolism and disposition of ethylene carbonate in male Fischer 344 rats.

Ethylene carbonate (EC) has a toxicity profile which resembles that of ethylene glycol (EG). To determine whether the toxicity of EC could be explained on the basis of its metabolism to EG, male Fischer 344 rats were given 200 mg/kg of uniformly labeled [14C]EC in water by gavage and the disposition of the radiolabel was then followed for 72 hr. EC was rapidly metabolized, with approximately 57 and 27% of the administered dose eliminated in the expired air as 14CO2 and in the urine, respectively; the remainder was found in the carcass. Separation of the urinary metabolites using liquid chromatography revealed a single radioactive peak. This metabolite was unequivocally identified as ethylene glycol via gas chromatography-mass spectrometry with the aid of 13C enrichment of the EC dose. Measurement of whole blood levels of EC and EG in rats given 200 mg/kg of EC by gavage revealed blood levels of EG approximately 100-fold higher than the levels of EC in these same animals, with a half-life of EG in blood of 2 hr, indicating rapid conversion of EC to EG. In a separate group of animals administered an equimolar dose of [14C]EG (141 mg/kg), approximately 37% of the dose was expired as 14CO2 and 42% was excreted in the urine as parent compound. When expressed on the basis of the ethanediol moiety, the disposition of EC was identical to that of EG. In view of the rapid and extensive biotransformation of EC to EG and the similarity of the existing (though limited) toxicity data base of EC compared to EG, utilization of the extensive EG systemic toxicity data base for assessing the safety of EC appears justified.

The effects of inhalation exposure to sulfuryl fluoride on fetal development in rats and rabbits.

Sulfuryl fluoride is a fumigant insecticide used for soils and permanent structures. Pregnant Fischer 344 rats and New Zealand White rabbits were exposed to 0, 25, 75, or 225 ppm of sulfuryl fluoride vapor via inhalation for 6 hr/day on Days 6-15 and 6-18 of gestation, respectively. Among rats, maternal water consumption was increased in the 225 ppm exposure group, but there were no indications of embryotoxicity, fetotoxicity, or teratogenicity in any of the exposed groups. Among rabbits, maternal weight loss during the exposure period (Days 6-18) was observed in the 225 ppm group. Decreased fetal body weights, considered secondary to maternal weight loss, were also observed at 225 ppm. However, no evidence of embryotoxicity or teratogenicity was observed among rabbits in any exposure group. Thus, inhalation exposure to sulfuryl fluoride was not teratogenic in either rats or rabbits exposed to levels of up to 225 ppm, and fetotoxic effects (reduced body weights) were observed among fetal rabbits only at an exposure level that produced maternal weight loss.

Teratologic evaluation of orally administered nitrapyrin in rats and rabbits.

Pregnant Fischer 344 rats and New Zealand White rabbits were orally administered 0, 5, 15, or 50 mg nitrapyrin/kg/day on Gestation Days 6 through 15 (rats) or 0, 3, 10, or 30 mg/kg/day on Gestation Days 6 through 18 (rabbits). In rats, 50 mg/kg/day produced slight histopathologic changes in the livers of pregnant females. Fetal examination revealed no evidence of fetotoxicity or teratogenicity among rats at dose levels up to 50 mg/kg/day. Among rabbits, a significant depression in maternal weight gain and increased absolute and relative liver weights were observed at 30 mg/kg/day. An increased incidence of crooked hyoid bone among fetal rabbits in the 30 mg/kg/day dose group was considered indicative of fetotoxicity but not teratogenicity. Thus, administration of nitrapyrin was not teratogenic at dose levels up to 50 mg/kg/day in rats and 30 mg/kg/day in rabbits.

Evaluation of the effects of inhalation exposure to 1,3-dichloropropene on fetal development in rats and rabbits.

1,3-Dichloropropene (DCP), which has found widespread use as a soil fumigant, was evaluated for its potential effects on embryonal and fetal development in rats and rabbits. Pregnant Fischer 344 rats and New Zealand White rabbits were exposed to 0, 20, 60, or 120 ppm of 1,3-dichloropropene for 6 hr/day during gestation Days 6-15 (rats) or 6-18 (rabbits). Exposure-related decreases in maternal weight gain and feed consumption were observed in rats at all treatment levels. Decreased weight gain was also observed among rabbits at 60 and 120 ppm. A slight, but statistically significant, increase in the incidence of delayed ossification of the vertebral centra in rats exposed in utero to 120 ppm of DCP was considered of little toxicologic significance in light of the maternal toxicity observed at this exposure concentration. No evidence of a teratogenic or embryotoxic response was observed in either species at any exposure level tested. Thus, it was concluded that DCP was not teratogenic at exposure levels up to 120 ppm in either rats or rabbits.

Embryotoxicity and fetotoxicity of orally administered tridiphane in mice and rats.

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane], a broad-leaf herbicide, was evaluated for its potential effects on mouse and rat embryonal and fetal development. Pregnant CF-1 mice were given 0, 25, 75, or 250 mg tridiphane/kg/day on Days 6 through 15 of gestation. Significant maternal toxicity was observed in both the 75- and 250-mg/kg/day dose groups. An increased percentage of females given 250 mg/kg/day showed implantation sites only after staining of the uterus, suggesting a toxic effect on the embryo during the early stages of development, possibly secondary to maternal toxicity. Increases in some skeletal variants were noted at the 75-mg/kg dose level; however, a teratogenic effect was not observed. An additional group of mice was given 250 mg/kg/day on Days 8 through 15 of gestation. Maternal toxicity was also observed among these mice as manifested by significantly elevated (+50%) liver weight; however, there was a substantial increase in the number of females with full-term litters following this shorter dosing period. An increase in the occurrence of cleft palate in these offspring associated with low fetal body weights was also observed. Pregnant Sprague-Dawley rats were given 0, 30, 100, or 200 mg/kg/day of tridiphane on Days 6 through 15 of gestation. Maternal toxicity was observed among rats given 200 mg/kg. Increased incidences of two minor skeletal variants, lumbar spurs and extra ribs, were observed in the 200-mg/kg/day dose group, and an increase in lumbar spurs was observed at 100 mg/kg/day. Thus, tridiphane was embryotoxic and induced cleft palate in mice only at the maternally toxic dose level of 250 mg/kg/day.(ABSTRACT TRUNCATED AT 250 WORDS)

Interpretation of oxygen disappearance curves measured in blood perfused tissues.

We have developed a two compartment (tissue and blood) lumped parameter model to interpret oxygen disappearance curves (O2 DCs) measured in vivo with PO2 microelectrodes in tissues which are perfused with blood. To include the properties of the oxyhemoglobin equilibrium curve (HEC), we used an algorithm we have recently developed for both standard and nonstandard conditions. The new blood and tissue model is more useful than a previous analysis using the Hill equation for blood and constant oxygen consumption (VO2). The model can be adapted for constant (zero-order) consumption, Michelis-Menten kinetics, or for double cytochrome systems. Examples for the former include brain, and for the latter, carotid body. The models are discussed in relationship to experimental microelectrode measurements in gerbil brain and in cat carotid body after blood flow occlusion.

A multicomponent, random walk model of transport and metabolism inside a neuron.

A model of multicomponent transport, consumption, and production of metabolites inside a neuron containing discrete mitochondria and glycolytic enzymes is developed using a random walk model of molecular transport. The ratio of anaerobic to aerobic metabolism which maximizes ATP production under normal, ischemic, and anoxic conditions is calculated. The ratio of the number of mitochondria to glycolytic enzymes which maximizes ATP under normal conditions is also calculated. Because the volume of the neuron is fixed, the sum of the number of mitochondria and glycolytic enzymes is fixed. This constraint is incorporated in the optimization process as an interior penalty function. Some of the advantages of employing the random walk technique are simple stoichiometry can be used to model consumption and production of metabolites, the geometry of the enzyme system and their active sites can be easily included in the model, and saturation of enzymes can be more easily modeled.

Measurement of solid feed consumption patterns in neonatal rats by 141Ce-radiolabeled microspheres.

Dams nursing litters of Fischer 344 rats were allowed access to feed containing nonabsorbable 141Ce-labeled NEN-TRAC microspheres for 24-hr intervals during the later half of a 28-day nursing period. Neonatal solid feed consumption began during the third week of nursing and rose to peak amounts as high as 2.1 times normal adult levels on a gram consumed per kilogram body weight per day basis at 28 days of age, with an average daily feed consumption (g kg-1 day-1) of approximately 1.5 times that normally eaten by adults. Feed consumption in lactating females peaked at concentrations as high as 3.2 times and averaged approximately 2.5 times the amount normally consumed by nonpregnant adult females of comparable age. These results should be considered when interpreting the results observed in reproduction studies when exposure is via feed. Effects which could be attributed to "enhanced neonatal sensitivity" may, in fact, merely reflect the toxicity resulting from increased chemical exposure. It is thus clear that, if reproduction studies are to be conducted at or near the MTD, adjustment of dietary concentration of test agents during lactation is necessary to maintain target dose levels and to prevent overexposure.

Teratogenic potential of inhaled dichlorobenzenes in rats and rabbits.

Orthodichlorobenzene (ODCB) and paradichlorobenzene (PDCB) were evaluated for teratogenic potential in rats (ODCB only) and rabbits. Groups of bred rats and inseminated rabbits were exposed to 0, 100, 200, or 400 ppm of ODCB; groups of inseminated rabbits were exposed to 0, 100, 300, or 800 ppm of PDCB. Animals were exposed for 6 hr/day on Days 6 through 15 (rats) or 6 through 18 (rabbits) of gestation. Maternal toxicity, as evidenced by a significant decrease in body weight gain, was observed in all groups of ODCB-exposed rats and liver weight was significantly increased in the 400-ppm ODCB-exposed group. Slight maternal toxicity was observed in groups of rabbits exposed to 400 ppm ODCB or 800 ppm PDCB as indicated by significantly decreased body weight gain during the first 3 days of exposure. Inhalation of up to 400 ppm of ODCB was not teratogenic or fetotoxic in rats, and neither ODCB nor PDCB was teratogenic or fetotoxic in rabbits at exposure levels up to 400 or 800 ppm, respectively.