Acute and subchronic toxicity of a nonsulfhydryl angiotensin-converting enzyme inhibitor.

Acute and 1-month toxicity studies with SCH 31846, a nonsulfhydryl anti-hypertensive agent which acts by inhibiting angiotensin-converting enzyme, were initiated to evaluate its toxicity. The oral LD50s in mice and rats were approximately 1.8 and 2.5 g/kg, respectively, while the iv LD50 was approximately 450 mg/kg in mice and 150 mg/kg in rats. Signs of acute toxicity in rats and mice included salivation, hypoactivity, ataxia, prostration, and convulsions. In a 1-month dog study at oral doses of 25, 75, or 150 mg/kg, there was a dose-related increase in emesis between 1 and 2 hr after dosing. Absorption studies showed peak blood concentrations occurring in dogs between 0.3 and 1 hr after dosing. No other noteworthy antemortem changes were observed. In a 1-month rat study at oral doses of 30, 180, or 600 mg/kg, the hematocrit and hemoglobin values of the 600 mg/kg-dosed female rats were slightly but significantly (p less than 0.05) decreased and the blood urea nitrogen was slightly but significantly (p less than 0.05) increased in all SCH 31846-dosed male rats and the 600 mg/kg-dosed female rats. Absorption studies in male rats at doses of 30, 180, and 600 mg/kg indicate that SCH 31846 is well absorbed in rats. The 150 mg/kg-dosed dogs and the 180- and 600 mg/kg-dosed rats had a slight increase in the number of renin-containing granules in the renal juxtaglomerular cells. No other compound-related microscopic changes were observed. These data are similar to data reported for Captopril and suggest that in the dog and rat the toxicity of ACE inhibitors is not dependent upon the presence or absence of a sulfhydryl group.

Effects of neonatal chlordecone exposure on pituitary-adrenal function in adult Fischer-344 rats.

Fischer-344 rat pups of either sex were injected on day four of age with 1 mg/pup chlordecone (CLD) or DMSO vehicle. At 77-78 days of age, the rats were subjected to a repeated stress-induced analgesia (SIA) paradigm. A white noise (conditioned stimulus; CS) was paired with scrambled footshock for approximately one-half of the rats, while the remaining rats were exposed to the CS only. Conditioning occurred over a seven day period, one trial per day. On day 8 all rats received the CS only; 15 min later, the rats were sacrificed and serum and adrenals collected for corticosterone and/or prolactin measurements. Although prior neonatal exposure to CLD had no effect on the acquisition of the conditioned response or the responsiveness of the adrenocortical system to the CS, basal levels of serum and adrenal corticosterone were generally depressed in CLD-exposed males. Basal serum prolactin levels were decreased and increased in CLD-exposed males and females, respectively. These data suggest that neonatal CLD exposure may serve as a chemical stressor that produces long-lasting alterations in basal pituitary-adrenocortical function. The expression of these effects also appeared to be sex-dependent.

Neurobehavioral assessment of 2,4-dichlorophenoxyacetic acid (2,4-D) in rats.

2,4-Dichlorophenoxyacetic acid (2,4-D), an organic acid commonly used as a herbicide, was assessed for behavioral and neurological toxicity in male Fischer-344 rats. When given by gavage twice weekly for 5 weeks, 2,4-D produced a significant increase in fore- and hindlimb grip strength. Other neurological measurements such as negative geotaxis, hindlimb splay, motor activity, and startle responsiveness, were not affected. A second experiment, in which rats were dosed 5 days per week for 4 weeks, replicated the finding that 2,4-D increases grip strength of rats. In addition, the neurological effect was found to dissipate with time following cessation of dosing. That 2,4-D increases grip strength may be related to the observation that it induces myotonia, a condition characterized by difficulty in relaxation of skeletal musculature following forceful contraction.

Effects of gestational and perinatal exposure to chlordecone (Kepone) on the neurobehavioral development of Fischer-344 rats.

Fischer-344 rats were exposed throughout gestation and the first 12 days of lactation to 1 or 6 ppm chlordecone via the maternal diet. Exposure to chlordecone had no effect on maternal weight gains after gestation nor did it affect birth weights, litter sizes, or sex ratio of the litters. Offspring tested at 30 and 100 days of age for behavioral performance showed no significant changes in fore- and hindlimb grip strength, spontaneous motor activity, startle responsiveness, or tail flick latencies to thermal stimulation. Negative geotaxis latencies were not affected at 30 days of age, but were increased in males at 100 days of age. Male rats exposed to chlordecone were found to be hypersensitive to the motility increasing effects of 1 mg/kg of apomorphine, which is a dopamine receptor agonist. In another pharmacological challenge with 2 mg/kg of d-amphetamine, a presynaptic releaser or dopamine and norepinephrine, the motility response was not significantly exaggerated in chlordecone exposed rats. These results suggest that fetal and neonatal exposure to chlordecone produces subtle alterations in the neurogenic function of rats.

Neurobehavioral effects following a single dose of chlordecone (Kepone) administered neonatally to rats.

Male and female Fischer 344 rat pups were exposed to either DMSO or chlordecone (Kepone) by s.c. injection on day 4 postnatally. Chlordecone had transient effects on body weights and resulted in precocial vaginal opening (vaginas open at day 21 of age). At approximately 100 days of age, one half of the animals were trained on a variable interval (VI) 15 sec schedule of food reinforcement. Rates of free operant activity differed during training of the VI and chlordecone-treated females had lower baselines than controls following establishment of baseline responding. Baselines of males were not affected. Chlordecone-exposed rats were affected the same as controls by d-amphetamine (0.25-2 mg/kg) and apomorphine (0.025-0.1 mg/kg). The remaining rats were trained to make a visually cued nose poke response for food in a discrete trial discrimination task. Few differences were noted during acquisition of the task over a three week period. However, marked alterations in responding were observed during two weeks of reversal. These data indicate that a single postnatal injection of chlordecone can produce subtle, long-lasting neurobehavioral changes in rats. The nature of these changes appear to be alterations in their reactivity to novel or changing conditions.

Neurobehavioral changes in adult Fischer 344 rats exposed to dietary levels of chlordecone (Kepone): a 90-day chronic dosing study.

Chlordecone (Kepone) given in the diet at 10 and 30 ppm for 90 days to adult male Fischer 344 rats produced significant behavioral changes. Rats were tested in a battery of behavioral screening tests for sensorimotor functions at 30, 60, and 90 days of dosing, and 30 days postdosing. Body weight loss was significant by 90 days of dosing with 30 ppm chlordecone; no weight change was seen at the lower dose. Variable effects on grip strength were seen during and after dosing. The magnitude of startle responsiveness to an air puff stimulus was significantly increased by 30 days of dosing in the 30 ppm dose group. Both 10 and 30 ppm doses produced increased responsiveness to an acoustic stimulus by 60 days of dosing. Negative geotaxis and tail flick response to thermal stimulation did not change. By 30 days postdosing, significant behavioral alterations still persisted in startle responsiveness.

The effects of acrylamide on the behavioral suppression produced by psychoactive agents.

Rats were trained to lever touch for food on a Variable Interval (VI) 15 sec. schedule of reinforcement. Dose-response alteration of VI responding by apomorphine, d-amphetamine, clonidine, and chlordiazepoxide was studied along and in the presence of a dose of acrylamide which, by itself, did not alter VI responding. Pretreatment with 12.5 mg/kg of acrylamide 24 hrs. prior to challenge with psychoactive compounds enhanced the behavioral suppressant effects of apomorphine and d-amphetamine. No significant effect of acrylamide pretreatment on the behavioral effects of clonidine and chlordiazepoxide was observed. These data suggest that acute exposure to acrylamide increases responsiveness to agents that act directly on dopamine (DA) receptors or indirectly by releasing DA. This change in responsiveness to apomorphine and d-amphetamine may be related to the effects of acrylamide on the affinity or density of the DA receptor.

Marked reduction in gonadal steroid hormone levels in rats treated neonatally with monosodium L-glutamate: further evidence for disruption of hypothalamic-pituitary-gonadal axis regulation.

Serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol-17 beta and testosterone were determined in adult rats that were treated in the neonatal period with monosodium L-glutamate (MSG) which has previously been shown to reliably produce destruction of arcuate nucleus perikarya. MSG-treated males had significantly smaller accessory sexual organs (seminal vesicles and ventral prostate) and tests and had significantly lower serum concentrations of FSH and testosterone than sex-matched controls. MSG-treated females had significantly lower serum concentrations of LH, FSH and estradiol-17 beta. Prolactin levels of MSG-treated rats were no different than sex-matched controls. This marked reduction in gonadal steroid levels (decreases 68%) and inappropriately low gonadotropin levels further characterizes the deficit of feedback regulation in the hypothalamic-pituitary-gonadal axis in MSG-treated rats.

Neonatal exposure to monosodium glutamate alters the neurobehavioral performance of adult rats.

On days 1-15 postpartum male and female Sprague-Dawley derived CD strain pups were dosed sc with either L-glutamic acid (MSG) (2-3.5 mg/g), 13% or 0.85% saline and tested at 67 and 102 days of age. At both periods, the body weights of MSG exposed males were less than the 13% exposed isosmotic controls. MSG exposed females, however, appeared to be obese compared to their controls at 102 days and exhibited a 50% incidence of tail-automutilation. Exposure to MSG did not affect the startle responsiveness of males or females to an acoustic startle stimulus. The startle responsiveness of females to a tactile air puff stimulus was significantly depressed in amplitude at 67 and 102 days; the response on the males at 67 days of age was also decreased, but the effect was not statistically significant. Fore- and hindlimb grip strength assessments indicated that MSG exposed females, at 102 days, had greater hindlimb grip strength. Forelimb grip strength was not affected in either sex. Tail flick latencies to a thermal stimulus were significantly elevated at 67 and 102 days of age in both MSG exposed sexes. Relative to the isosmotic control group, spontaneous motor activity of MSG exposed animals was found to be consistently lower. Exposure to MSG did not, however, change the responsiveness of either sex to the motor activity stimulating effects of a d-amphetamine challenge (0.3-3 mg/kg). These results indicate that postnatal exposure to MSG produced measurable, long-term behavioral and somatic alterations in female and, to a lesser degree, male rats.

Monosodium glutamate exposure in the neonate alters hypothalamic and pituitary neuropeptide levels in the adult.

Administration of monosodium glutamate (MSG) during the neonatal period in rats produced differential effects on the contents of various neuropeptides in the hypothalamus: beta-endorphin (beta-E) level was reduced by 70% while substance P (SP), neurotensin (NT) and Met5-enkephalin (ME) levels were not significantly changed (ME content of male rats was slightly reduced). The contents of ME, SP and NT in striatum and hippocampus were also unaffected by the same treatment. Male rats contain higher pituitary content of beta-endorphin-like immunoreactivity (beta-ELI) than female rats. MSG treatment reduced the pituitary content of beta-ELI and abolished the sex difference in beta-ELI level seen in the control rats. MSG treatment in the neonates by eliminating beta-E neurons while sparing ME neurons in the brain may be a useful tool for studying the different functions of these two separate opioid peptides.

Neurotransmitter receptors in brain regions of acrylamide- treated rats. I: Effects of a single exposure to acrylamide.

A single oral dose of acrylamide (25 or 50 mg/kg) increased the level of striatal 3H-spiroperidol binding in six week old male rats. This enhanced dopamine receptor activity was specific since treatment caused no significant changes in glycine, serotonin, and muscarinic cholinergic binding. At the highest acrylamide dose tested (100 mg/kg), elevations of the medullary glycine and frontal cortical serotonin receptors were also found. Pretreatment of animals with a blocker of hepatic mixed function oxidase (SKF 525a) or a thiol blocker (methylmercuric chloride) prevented the acrylamide-induced elevation of striatal spiroperidol binding, indicating that the causative agent was a secondary metabolite of acrylamide. Apomorphine-induced motility was significantly attenuated by 24 hr predosing with acrylamide, suggesting a change in the sensitivity of the dopamine receptor. The behavioral relevance of observed biochemical changes was thus shown by the altered response of treated animals to apomorphine.

Effects of acrylamide given during gestation on dopamine receptor binding in rat pups.

Acrylamide (20 mg/kg) was administered by gavage to time-pregnant Fischer 344 rats daily from day 7 to day 16 of gestation. Acrylamide did not affect the number, size, or body weights of litters obtained but did decrease the [3H]spiroperidol binding in striatal membranes of 2-week-old pups. This effect could not be seen at 3 weeks of age. Scatchard analysis showed that acrylamide changed the affinity as well as the number of dopamine receptor sites. There were no signs of maternal toxicity in dosed mothers as evaluated by their body weights or general appearance.

Postnatal exposure to benzene alters the neurobehavioral functioning of rats when tested during adulthood.

Male and female rats of the Fischer Strain were dosed with 550 mg/kg of benzene or corn oil vehicle on Days 9, 11 and 13 postpartum. The spontaneous motor activity of benzene exposed rats (males and females) was found to be elevated when tested at 100-130 days of age. When challenged with various doses of d-amphetamine (0.3-3 mg/kg), the benzene exposed rats were found to be less sensitive to the motor activity increasing effects of the drug. In a subsequent test to measure specific components of exploratory activity in an operant chamber (nose-poking, wall rearing, lever touching), female rats exposed to benzene were found to emit fewer rearing responses. Body weights and performance in a battery of tests to assess neurobehavioral toxicity (Days 45, 60 and 100 postpartum) were not affected by postnatal exposure to benzene. These data indicate that postnatal exposure to benzene can produce significant alterations in the motor activity of rats when tested during adulthood and the type of effect depended on the procedure used. Changes in the sensitivity of benzene exposed animals to d-amphetamine suggest long-term alterations in catecholaminergic function.

Effect of food toxicants on voluntary wheel running in rats.

Voluntary wheel running in rats in reaction to a dietary deficiency of iron or food toxicants of natural (dioscin) and environmental (cadmium) origins was used to develop a behavioral model by which rapid detection of food contaminants was accomplished following induction of spontaneous activity by techniques of feed restriction. High levels of voluntary wheel running in reference controls were followed by significant depressions in running activity in animals fed the dietary toxicants. Analyses of blood and liver tissues and depressions of testes size confirmed the presence of the insults to metabolism.

Effect of treadmill speeds and slopes on voluntary exercise in rats.

Male rats 87 days of age were given daily 90-minute sesions of voluntary exercise on self-operated treadmills pre-set to deliver speeds ranging from 6.1 to 73.2 m/minute and slopes of 0 to 27 degrees. Voluntary motivation to operate the treadmills was induced by maintaining the rats at constant body weights of 203 +/- 2 g. Under the conditions of the experiment, the rats selected 24.4 m/minute and 0 degree slope with running bursts averaging 21 to 24 seconds in duration as a preferred condition for greatest running. Since all activity was voluntary, the consistent patterns of running bursts at 24.4 m/minute are believed to be potentially capable of serving as reference baselines for detection of food contaminants, toxicants and other insults to normal metabolic processes.