Developmental neurotoxicity evaluation of the avermectin pesticide, emamectin benzoate, in Sprague-Dawley rats.

The potential of emamectin benzoate (EB) to cause developmental neurotoxicity in Sprague-Dawley rats was assessed using a study design by the US EPA. Dosages of 0 (deionized water), 0.1, 0.6, or 3.6 mg/kg/day were administered at 5 ml/kg by oral gavage from gestational day (GD) 6 to lactational day (LD) 20 to groups of 25 mated females each. Between GD 17 and 20 the high dose was reduced to 2.5 mg/kg/day because of pup tremors observed at this dose level in a concurrent two-generation study. Females were allowed to deliver and the young were evaluated for survival, growth, development, behavior, and histological changes to brain, spinal cord, peripheral nerve, and skeletal muscle. Behavioral assessment of the offspring consisted of open field motor activity, auditory startle habituation, and passive avoidance tests; each was conducted on weanling and adult animals (one animal/sex/litter). Histopathological examination of the CNS and PNS was conducted on one animal/sex/litter on postnatal days (PND) 11 and 60. There were significant increases in average F0 maternal body weight gains during gestation in the 0.6 and 3.6/2.5 mg/kg/day groups, but no other effects were observed in pregnant females of these or the low-dose groups during the study. Beginning on PND 6, tremors were observed in high-dose pups, and this was followed by hindlimb splay in all high-dose pups by PND 15-26. Both of these physical signs disappeared by PND 34 (i.e., 10-11 days after weaning). There were no compound-related deaths in F1 offspring. Beginning on PND 11, progressive decreases in preweaning average weights were observed in the high-dose group (to 42% below control in females on PND 21). Average weight gain during the postweaning period was significantly decreased in the 3.6/2.5 mg/kg/day group. There were EB-related effects in behavioral tests only in the high-dose group. A significant increase in PND 13 average horizontal motor activity was due to stereotypical movements. Average horizontal activity was decreased on PND 17 and in adult females, but there was no effects on PND 21. Average peak auditory startle response amplitude was decreased on PND 22 and in adults. There were no EB-related effects in the passive avoidance test, relative brain weights, or in the histological examination (including morphometry) of the nervous system. These results demonstrate that the high-dose EB exposure during gestation and lactation to rats produced evidence of neurotoxicity in the F1 offspring, and a clear No Observed Adverse Effect Level (NOAEL) for developmental neurotoxicity of EB was determined to be 0.6 mg/kg/day.

Effects of carbon dioxide, fertilization, and irrigation on photosynthetic capacity of loblolly pine trees.

Branches of nine-year-old loblolly pine trees grown in a 2 x 2 factorial combination of fertilization and irrigation were exposed for 11 months to ambient, ambient + 175, or ambient + 350 micro mol mol(-1) CO(2). Rates of light-saturated net photosynthesis (A(max)), maximum stomatal conductance to water vapor (g(max)), and foliar nitrogen concentration (% dry mass) were assessed monthly from April 1993 until September 1993 on 1992 foliage (one-year-old) and from July 1993 to March 1994 on 1993 foliage (current-year). Rates of A(max) of foliage in the ambient + 175 CO(2) treatment and ambient + 350 were 32-47 and 83-91% greater, respectively, than that of foliage in the ambient CO(2) treatment. There was a statistically significant interaction between CO(2) treatment and fertilization or irrigation treatment on A(max) on only one measurement date for each age class of foliage. Light-saturated stomatal conductance to water vapor (g(max)) was significantly affected by CO(2) treatment on only four measurement dates. Light-saturated g(max) in winter was only 42% of summer g(max) even though soil water during winter was near field capacity and evaporative demand was low. Fertilization increased foliar N concentration by 30% over the study period when averaged across CO(2) treatments. During the study period, the ambient + 350 CO(2) treatment decreased average foliar N concentration of one-year-old foliage in the control, irrigated, fertilized and irrigated + fertilized plots by 5, 6.4, 9.6 and 11%, respectively, compared with one-year-old foliage in the corresponding ambient CO(2) treatments. The percent increase in A(max) due to CO(2) enrichment was similar in all irrigation and fertilization treatments and the effect persisted throughout the 11-month study period for both one-year-old and current-year foliage.

Defining the susceptible period of developmental toxicity for the AT1-selective angiotensin II receptor antagonist losartan in rats.

Previous developmental and reproductive toxicity studies conducted in rats with Losartan, a potent AT1 subtype selective angiotensin II receptor antagonist, noted treatment-related effects on the pups of dams treated beyond the second trimester through lactation, as demonstrated by increases in pre- and postweaning pup deaths and decreased pup body weights [Spence et al. (1995) Teratology 51:000-000]. The studies presented here were designed to define the critical period for the induction of neonatal toxicity and to examine the effects of Losartan on kidney development when the drug is administered to the dam beyond the second trimester through lactation. In a developmental toxicity study with postweaning evaluation, pregnant rats were administered 5, 20, and 100 mg Losartan/kg/day on gestation days 6 through 15 (GD 6-15). There were no adverse effects on the F1 generation as assessed by mortality, clinical signs, weight gain, external examinations, developmental signs, behavioral tests, and gross or microscopic examination of the kidney. In a fostering/cross-fostering study, pregnant rats were administered 100 mg Losartan/kg/day on GD 15 through lactation day 20 (LD 20). Following delivery, pups from dams treated with Losartan were fostered to control dams, pups from control dams were fostered to Losartan-treated dams, and pups were also fostered to dams within the same group. Maternal exposure to Losartan during lactation increased the incidence of pup deaths on postnatal days 1-3 (PND 1-3), caused decreased pup weights on PND 7, and decreased performance in the auditory startle test in females and increased performance on the second swim maze test in males, relative to controls. Maternal exposure to Losartan during gestation was associated with decreased pup weight on PND 21 and effects observed on male performance in the swim maze test. Treatment during gestation was also associated with decreased pup cardiac weight as well as drug-induced histopathological changes of the kidneys from F1 pups, including medial hypertrophy of intracortical arterioles and dilatation of the renal pelvis. While the cardiac and renal vascular effects disappeared with time, significant renal lesions were still evident by PND 90. In a late-gestation/lactation study with renal evaluation, pregnant rats were administered 0.5, 1.0, 5.0, 20, and 100 mg Losartan/kg/day on GD 15-LD 20. Maternal toxicity was evident as decreased body weight gain in the 100 mg Losartan/kg/day group.(ABSTRACT TRUNCATED AT 250 WORDS)

The toxicity of a fluorinated-biphenyl HMG-CoA reductase inhibitor in beagle dogs.

L-645, 164, a potent inhibitor of hydroxymethylglutarylcoenzyme A (HMG-CoA) reductase, is a structurally unique, synthetic monofluorinated-biphenyl that was administered to beagle dogs at dosages of 2, 10, or 50 mg/kg/day for 14 weeks to evaluate its toxic potential. Previously tested HMG-CoA reductase inhibitors from this laboratory have either been semisynthetic or fermentation-derived products containing a hexahydronaphthalene ring structure (i.e., lovastatin and simvastatin). Administration of L-645, 164 produced a significant spectrum of lesions, some of which have been previously associated with compounds of this pharmacological class, while others were unique to this monofluorinated-biphenyl inhibitor. Subcapsular lenticular opacities were produced in six of eight of the dogs receiving 50 mg/kg/day of L-645, 164 within 8 weeks of dosing. One dog receiving this dosage level experienced increases in serum alanine aminotransferase activity to levels 10 times those in concurrent control dogs. Light and electron microscopy of a wedge biopsy obtained within 3 days of this transaminase elevation failed to reveal any significant changes and the elevation resolved spontaneously despite continued drug administration. Lesions of the optic nerve and acoustic-vestibular tract and trapezoid decussation were observed in several dogs receiving 50 mg/kg/day. In addition, similar changes were observed in the optic tract in several of the dogs receiving 50 mg/kg/day and in one dog receiving 2 mg/kg/day of L-645,164. These were unique to L-645,164 and have not been observed after the administration of other HMG-CoA reductase inhibitors in this laboratory. Optic tract changes were generally mild, consisting of small to medium vacuoles without apparent myelin loss. Lesions in the other areas ranged from very slight to prominent vacuolation. No clinical signs were observed. Peak plasma drug levels of L-645,164 at 50 mg/kg were greater than 5 micrograms/ml, about one order of magnitude greater than those attained after administration of pharmacologically equipotent doses of lovastatin and simvastatin. These findings support previous observations that HMG-CoA reductase inhibitors producing high plasma drug levels are associated with a significant degree of systemic toxicity. In addition, the drug-induced CNS lesions attributed to L-645,164 appear also to be related to its chemical structure since similar lesions have not been observed after the administration of other structurally unrelated HMG-CoA reductase inhibitors that produce high plasma drug concentrations and comparable degrees of serum cholesterol lowering.

Chromosomal abnormalities and gene amplification in renal cancers induced in rats by nickel subsulfide.

Nickel subsulfide (alpha Ni3S2) was administered to male Fischer-344 rats by unilateral intrarenal (i.r.) injection (20 mg per rat) to establish the time-course of alpha Ni3S2-induced erythrocytosis and to identify chromosomal abnormalities and molecular genetic aberrations in ensuing renal cancers. Blood hematocrit values were increased in alpha Ni3S2-treated rats during two to 36 weeks post-injection, attained a maximum of 77 percent (SD +/- 5) at 16 weeks (vs 51 +/- 3 percent in vehicle controls), and returned to baseline at 40 weeks. Within 21 months, malignant neoplasms (five sarcomas, one carcinoma) occurred in the injected kidneys of 6/28 alpha Ni3S2-treated rats (vs 0/13 controls). Cytogenetic analyses of direct preparations or primary cell cultures showed prominent chromosomal aberrations in three neoplasms, with rearranged marker chromosomes, polyploidy, and in one case an homogeneously staining region (HSR). Assays for gene amplification were performed with probes for murine erythropoietin (EPO) gene and H-ras, c-fos, c-myc, and N-myc oncogenes, using deoxyribonucleic acid (DNA) samples isolated from injected kidneys and renal neoplasms, as well as from the contralateral, non-injected kidneys. No consistent pattern was found; in one sarcoma, N-myc was amplified six-fold and c-fos was amplified two-fold; in another sarcoma, H-ras, c-fos, and EPO were amplified two-fold. This study shows that (a) karyotypes of 3/6 renal neoplasms of alpha Ni3S2-treated rats contained prominent marker chromosomes, (b) oncogene amplification was noted in 2/6 renal neoplasms, and (c) the EPO gene was not consistently amplified in DNA from the injected kidneys of alpha Ni3S2-treated rats during the initiation of erythrocytosis, or in subsequent renal neoplasms.

Rapid induction of an experimental metastatic phenotype in first passage rat embryo cells by cotransfection of EJ c-Ha-ras and c-myc oncogenes.

First passage rat embryo cells were transfected with plasmids carrying a mutated EJ c-Ha-ras oncogene alone or in combination with the c-myc oncogene. Three days later, unselected cultures were harvested and injected into nude mice either subcutaneously to assay for tumorigenicity or intravenously to assay for metastasis to the lung. The results indicate that a transcriptionally-enhanced EJ-c-Ha-ras oncogene alone can convert normal rat cells to a tumorigenic but not metastatic phenotype. Co-transfection of a c-myc oncogene with the EJ c-Ha-ras oncogene was necessary to produce the rapid, phenotypic conversion of normal cells to transformed cells with both tumorigenic and metastatic potential. No tumors were observed in animals injected with c-myc-transfected cells. Cell lines established from EJ c-Ha-ras-induced shoulder tumors were metastatic when reinjected intravenously into nude mice. These results support the hypothesis that the cooperative action of c-Ha-ras and c-myc oncogenes is more potent in inducing malignant transformation than either oncogene acting alone. Our results also suggest that the phenotypic conversion of normal cells to tumorigenic cells with experimental metastatic potential by ras and myc oncogenes can be completed within 3-4 cell divisions after transfection.

Malignant transformation of a preneoplastic hamster epidermal cell line by the EJ c-Ha-ras-oncogene.

We have investigated whether the activation of endogenous ras genes is associated with the immortalization or malignant transformation of primary hamster epidermal cells by chemical carcinogens. We have also asked whether transfection of a cloned c-Ha-ras oncogene (pEJ) into a nontumorigenic cell line established from hamster epidermal cells by N-methyl-N'-nitro-N-nitrosoguanidine treatment can induce conversion to a malignant phenotype. DNA from the nontumorigenic epidermal cell line (H5-MNNG) and from two neoplastic cell lines transformed by benzo(a)pyrene was not capable of transforming NIH/3T3 cells. This result suggests that these cells do not contain an activated (mutated) ras gene. However, when H5-MNNG cells were cotransfected with pEJ and pSV2-gpt, a plasmid containing the dominant selectable marker gene Ecogpt, seven of nine clones of Ecogpt transformants formed carcinomas in nude mice and colonies in soft agar. Southern blot analysis of BamHl-digested genomic DNA from the Ecogpt-transformed clones indicated that rapid malignant transformation was associated with integration of a complete copy of the 6.6-kilobase fragment of pEJ containing the activated c-Ha-ras gene. Furthermore, DNA from the malignant clones transformed NIH/3T3 cells in a secondary transfection assay. These studies demonstrate that a mutated c-Ha-ras gene, under the transcriptional control of its normal cellular promoter, can rapidly transform a nontumorigenic epidermal cell line. This result suggests that activation of an endogenous c-ras gene can function as the final completing event in the progression of epithelial cells to the malignant phenotype. Thus, preneoplastic cell lines of both mesenchymal and epithelial origin have now been shown to be susceptible to malignant conversion by a single mutation in a c-Ha-ras proto-oncogene.

Effect of tamoxifen on H-Y antigen expression and gonadal development in chicken embryos.

Avian species follow the ZW/ZZ system of sex determination, which the female is heterogametic and expresses H-Y (or, more appropriately, 'H-W') antigen. We present the results of an investigation into the effects of the antiestrogen, tamoxifen, on gonadal differentiation and H-Y antigen expression in chickens. When given at doses of 0.25-2 mg per egg immediately before incubation, tamoxifen blocked regression of the right gonad in a significant number of 14-day-old female embryos. The nonregressed right gonad had a testis-like external appearance and, in some cases, contained what appeared to be spermatogenic tubules. Tamoxifen had no histologically detectable effect on the differentiation of the left ovary or the testes. In spite of tamoxifen's histological effects on right female gonads, it did not masculinize the steroidogenic capabilities of these gonads. Whether obtained from drug- or vehicle-treated embryos, the left and right female gonads always contained appreciable amounts of estrogen. In contrast, testes obtained from either drug- or vehicle-treated embryos did not contain detectable amounts of estrogen. Tamoxifen reduced the H-Y antigen levels in female liver and gonads. In both left and right female gonads, the reduction was to male levels. In female livers, tamoxifen reduced H-Y antigen to levels intermediate between those of normal males and females. Thus, the expression of H-Y antigen in both gonadal and nongonadal tissue is estrogen dependent, but the dependency appears to be more stringent for gonadal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Diflunisal-induced maternal anemia as a cause of teratogenicity in rabbits.

Diflunisal [5-(2,4-difluorophenyl)-salicylic acid] is a new analgesic antiinflammatory drug that, when administered orally to rabbits at 40 and 60 mg/kg/day, caused terata, most commonly axial skeletal defects. These same dosage levels also caused a severe maternal hemolytic anemia following a dramatic decrease in erythrocyte ATP levels. The teratogenicity, anemia, and depletion of ATP were unique to the rabbit among species examined. To test the possible causality between the teratogenic effects and anemia induced by diflunisal, a single dose of 180 mg/kg diflunisal was administered to rabbits on gestation day 5. This treatment produced an anemia that persisted through gestation day 15 in addition to causing the characteristic axial skeletal defects. Since diflunisal was cleared from maternal blood before gestation day 9, the critical day for induction of similar axial skeletal defects by hypoxia, the skeletal malformations probably resulted from maternal hypoxia secondary to anemia and not from a direct and specific effect of the drug on the embryo. In addition, we observed that the diflunisal level in the embryo was less than 5% of the peak maternal blood level probably as a result of high plasma protein binding of diflunisal in the maternal blood (greater than 98%). This relatively low placental transfer may explain the lack of diflunisal teratogenicity in rats and mice compared to aspirin which crosses the placenta more readily. These studies demonstrate that a species that exhibits unusually severe drug-specific maternotoxicity is probably an unsuitable model for the prediction of the teratogenic potential of that drug in humans.

Cyclophosphamide induces osteopetrosis in rats.

The effect of a single oral dose of cyclophosphamide in six-week old random outbred albino rats on hematologic, immunologic, and pathologic parameters was studied. As expected, doses that decreased the number of circulating lymphocytes and suppressed the blastogenic response to Concanavalin A, a T cell mitogen, also caused extramedullary hematopoiesis in the liver and spleen and depletion of cortical lymphocytes in lymph nodes. However, a novel histomorphologic finding of this study was osteopetrosis. It would appear that cyclophosphamide interferes with a subpopulation of lymphoid cells that are involved in the formation of osteoclastic cells.

Indomethacin and aspirin: effect of nonsteroidal anti-inflammatory agents on the rate of fracture repair in the rat.

A total of 210 male Charles River CD rats, 45 days old, were subjected to a fracturing of the right radius and ulna by digital pressure while under ether anesthesia. These animals were then assigned randomly to dose groups (1, 2 or 4 mg/kg/day of indomethacin and 100, 200, or 300 mg/kg/day of aspirin) and were dosed for 21 days. Dose levels were chosen to provide approximately equipotent levels of the test compounds with the highest dose approaching toxicity. Radiographs were taken of control-rat fractures on days 8, 14, and 21. Three rats at 4 mg/kg/day of indomethacin died of interstinal perforation prior to scheduled sacrifice. On day 22, all remaining rats were sacrificed by exsanguination under anesthesia. Histologic secretions of the radius and ulna were examined in random sequence without knowledge of the treatment regimen. A histologic grade based on the morphologic stage of fracture healing was given. There was a drug- and dose-related retardation of fracture healing, which was statistically significant at all dose levels of indomethacin and the highest level of aspirin, as compared to controls. Decreased mean grades in the groups given 100 and 200 mg/kg/day of aspirin, though not statistically significant, suggest a retarding effect on fracture healing at these levels also. No statistically significant changes in numbers of pseudoarthroses were found.

Aspirin: teratogenic evaluation in the dog.

Beagle bitches were administered aspirin at either 100 or 400 mg/kg/day between Days 15 and 22 or Days 23 and 30 postmating, and corresponding control groups were dosed with vehicle during one of these same time periods. Maternotoxicity was evident in all dogs dosed with 400 mg/kg/day of aspirin, but no signs of toxicity were observed when 400 mg/kg/day of aspirin was administered from Days 15 to 22 postmating. Teratogenicity, as evidenced by 50% malformation rate, was seen in fetuses from dams treated with 400 mg/kg/day on Days 23 to30 postmating. Observed malformations included, but were not limited to cleft palate,micrognathia, anasarca, cardiovascular malformations, and tial anomalies. No evidence of embryotoxic or teratogenic effects was seen in fetuses from either 100 mg/kg/day dosage level group. Examination of fetuses from 12 untreated litters and 4 vehicle-control litters revealed a very low spontaneous malformation rate confined almost entirely to minor tail abnormalities. These data support use of the dog as an acceptable alternative species in teratogenic screening.

Trigonal-colonic anastomosis: a urinary diversion procedure in dogs.

Trigonal-colonic anastomosis for diversion of urine into the colon was performed in 12 clinically normal dogs and in 10 incontinent dogs with diseases of the urinary bladder or urethra. Dogs were studied from 1 to 30 months after surgery. The surgical procedure was technically satisfactory. Fifteen of 22 dogs were studied with intravenous urography, and only 1 case of hydronephrosis was found. Pyelitis was a common histopathologic finding in both groups of dogs. Pyelonephritis developed in 30% of dogs, regardless of duration of anastomosis. Glomerular filtration rate was reduced in all dogs studied, but renal failure was infrequent. Values for blood urea nitrogen and serum inorganic phosphorus were elevated due to intestinal recycling of nitrogenous products and phosphate. Electrolyte imbalances were not a problem, but gastrointestinal disturbances developed in 3 of the 10 diseased dogs. Six of 10 diseased dogs survived from 9 months to more than 3 years. Trigonal-colonic anastomosis appears to be a satisfactory salvage procedure for incontinent dogs with diseases of the urinary bladder or urethra that do not respond to other forms of therapy.