The effects of feed restriction on reproductive function in Swiss CD-1 mice

Impact of chronic vitamin A excess on sperm morphogenesis in mice

BACKGROUND

The increasing availability of fortified foods and supplements has caused an overconsumption of vitamin A (VA), above the recommended level. To date, the effects of chronic VA excess (VAE) on spermatogenesis remain unclear.

OBJECTIVE

This study aims to investigate the long-term excessive intake of VA effects on spermatogenesis in mice.

MATERIALS AND METHODS

Dams were initially fed a control diet (4 IU/g) or a VAE diet (250 IU/g), 4 weeks prior to mating and during pregnancy. Dams and their male pups continued this diet regimen until the offspring reached 12 weeks of age. At 12 weeks of age, epididymis caudal spermatozoa and testes were collected. For histological analysis, sections were stained with periodic acid-Schiff-hematoxylin, and quantitative PCR was used to detect changes in gene expression in the testes of the VAE mice. Sperm motility and morphology were evaluated to detect the endpoint of VAE toxicity.

RESULTS

Body weights were not significantly different between the control and VAE groups. Testicular cross-sections from the control and VAE mice contained a normal array of germ cells, and the daily sperm production was similar between the two groups. However, the percentage of seminiferous tubules in stages VII and VIII was significantly lower in the VAE mice than in the control. In addition, significant changes in the expression of genes involved in retinoid metabolism, spermatogenesis, and spermiogenesis were detected in the testes of the VAE mice. Consistently, sperm motility and head morphology were significantly impaired in the VAE mice.

DISCUSSION AND CONCLUSION

Our findings suggest that long-term dietary intake of VAE was able to influence both pre- and post-meiotic spermatogenesis. As a result of testicular toxicity, we demonstrated, to the best of our knowledge, for the first time that long-term VAE caused sperm-head abnormalities.

Butylparaben multigenerational reproductive assessment by continuous breeding in Hsd:Sprague Dawley SD rats following dietary exposure

Butylparaben (BP) is an antimicrobial agent utilized for decades as a preservative in numerous consumer products. The safety of parabens has recently come under scrutiny based on reports of estrogenic activity and suggested adverse effects upon the reproductive system. Due to the limited availability of studies that address the potential for BP exposure to induce reproductive toxicity, and clear evidence of human exposure, the National Toxicology Program conducted a multigenerational continuous breeding study to evaluate the impact of dietary BP-exposure at 0, 5000, 15,000, or 40,000 ppm on reproductive and developmental parameters in Hsd:Sprague Dawley SD rats. BP-exposure was not associated with adverse alterations of fertility, fecundity, pubertal attainment, or reproductive parameters in F0, F1, or F2 generations. Exposure-dependent increases in liver weights, and incidences of non-neoplastic liver lesions suggest the liver is a target organ of BP toxicity. No findings were observed that would support the purported mechanism of BP-induced endocrine disruption in perinatally-exposed rodents.

Diabesity: A Polygenic Model of Dietary-Induced Obesity from Ad Libitum Overfeeding of Sprague–Dawley Rats and Its Modulation by Moderate and Marked Dietary Restriction

This study compared the effects of ad libitum (AL) overfeeding and moderate or marked dietary restriction (DR) on the pathogenesis of a metabolic syndrome of diabesity comprised of age-related degenerative diseases and obesity in a outbred stock of Sprague–Dawley (SD) rats [Crl:CD (SD) IGS BR]. SD rats were fed Purina Certified Rodent Diet AL (group 1), DR at 72–79% of AL (group 2), DR at 68–72% of AL (group 3) or DR at 47–48% of AL (group 4) for 106 weeks. Interim necropsies were performed at 13, 26, and 53 weeks, after a 7-day 5-bromo-2-deoxyuridine (BrdU)-filled minipump implantation. Body weights, organ weights, carcass analysis, in-life data including estrous cyclicity, and histopathology were determined. At 6–7 weeks of age SD rats had 6% body fat. AL-feeding resulted in hypertriglyceridemia, hypercholesterolemia, and dietary-induced obesity (DIO) by study week 14, with 25% body fat that progressed to 36–42% body fat by 106 weeks. As early as 14 weeks, key biomarkers developed for spontaneous nephropathy, cardiomyopathy, and degenerative changes in multiple organ systems. Early endocrine disruption was indicated by changes in metabolic and endocrine profiles and the early development and progression of lesions in the pituitary, pancreatic islets, adrenals, thyroids, parathyroids, liver, kidneys, and other tissues. Reproductive senescence was seen by 9 months with declines in estrous cyclicity and pathological changes in the reproductive organs of both sexes fed AL or moderate DR, but not marked DR. The diabesity syndrome in AL-fed, DIO SD rats was readily modulated or prevented by moderate to marked DR. Moderate DR of balanced diets resulted in a better toxicology model by significantly improving survival, controlling adult body weight and obesity, reducing the onset, severity, and morbidity of age-related renal, endocrine, metabolic, and cardiac diseases. Moderate DR feeding reduces study-to-study variability, increases treatment exposure time, and increases the ability to distinguish true treatment effects from spontaneous aging. The structural and metabolic differences between the phenotypes of DIO and DR SD rats indicated changes of polygenic expression over time in this outbred stock. AL-overfeeding of SD rats produces a needed model of DIO and diabesity that needs further study of its patterns of polygenic expression and phenotype.

A Mechanistic Basis for the Beneficial Effects of Caloric Restriction On Longevity and Disease: Consequences for the Interpretation of Rodent Toxicity Studies

Caloric restriction in rodents has been repeatedly shown to increase life span while reducing the severity and retarding the onset of both spontaneous and chemically induced neoplasms. These effects of caloric restriction are associated with a spectrum of biochemical and physiological changes that characterize the organism's adaptation to reduced caloric intake and provide the mechanistic basis for caloric restriction's effect on longevity. Here, we review evidence suggesting that the primary adaptation appears to be a rhythmic hypercorticism in the absence of elevated adrenocorticotropin (ACTH) levels. This characteristic hypercorticism evokes a spectrum of responses, including reduced body temperature and increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, reduced oxidative damage to proteins and DNA, reduced reproductive capacity, and altered drug-metabolizing enzyme expression. The net effect of these changes is to (1) decrease growth and metabolism in peripheral tissues to spare energy for central functions, and (2) increase the organism's capacity to withstand stress and chemical toxicity. Thus, caloric restriction research has uncovered an evolutionary mechanism that provides rodents with an adaptive advantage in conditions of fluctuating food supply. During periods of abundance, body growth and fecundity are favored over endurance and longevity. Conversely, during periods of famine, reproductive performance and growth are sacrificed to ensure survival of individuals to breed in better times. This phenomena can be observed in rodent populations that are used in toxicity testing. Improvements over the last 30 years in animal husbandry and nutrition, coupled with selective breeding for growth and fecundity, have resulted in several strains now exhibiting larger animals with reduced survival and increased incidence of background lesions. The mechanistic data from caloric restriction studies suggest that these large animals will also be more susceptible to chemically induced toxicity. This creates a problem in comparing tests performed on animals of different weights and comparing data generated today with the historical database. The rational use of caloric restriction to control body weight to within preset guidelines is a possible way of alleviating this problem.

Guidance on classification for reproductive toxicity under the globally harmonized system of classification and labelling of chemicals (GHS)

The Globally Harmonised System of Classification (GHS) is a framework within which the intrinsic hazards of substances may be determined and communicated. It is not a legislative instrument per se, but is enacted into national legislation with the appropriate legislative instruments. GHS covers many aspects of effects upon health and the environment, including adverse effects upon sexual function and fertility or on development. Classification for these effects is based upon observations in humans or from properly designed experiments in animals, although only the latter is covered herein. The decision to classify a substance based upon experimental data, and the category of classification ascribed, is determined by the level of evidence that is available for an adverse effect on sexual function and fertility or on development that does not arise as a secondary non-specific consequence of other toxic effect. This document offers guidance on the determination of level of concern as a measure of adversity, and the level of evidence to ascribe classification based on data from tests in laboratory animals.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Assessment of circulating hormones in regulatory toxicity studies II. Male reproductive hormones

When test article-related testicular toxicity or Leydig cell tumors are identified in nonclinical studies, the measurement of circulating hormones such as luteinizing hormone, follicle-stimulating hormone, inhibin, testosterone, or prolactin is often considered in order to aid mechanistic investigations or to identify potential biomarkers in man. Although some hormone levels are relatively constant, others are subject to wide variability owing to pulsatility of secretion, diurnal rhythms, and stress. To avoid being misled, it is important that this variation is factored into any study design that includes hormone measurements. Since all these possibilities start from the pathologist's reading of the tissue sections, we begin with a review of the morphologic changes that are tied to underlying alterations in hormones. We then provide the reader with basic information and representative hormone data, including coefficients of variation, for the major male reproductive hormones in the three main nonclinical species (rats, dogs, and cynomolgus monkeys). Power and probability tables for rats and dogs allow estimates of the number of animals or samples needed to provide a given likelihood of detecting a hormonal change of a given size. More importantly, we highlight the variability of this process and the real value in readers developing this information at their own site.

Initial insights regarding the role of p53 in maintaining sperm DNA integrity following treatment of mice with ethylnitrosourea or cyclophosphamide

If p53 is essential to eliminate damaged spermatogenic cells, then mutagen exposure in the absence of p53 would increase sperm containing damaged DNA. p53 knockout (-/-, NULL) and wild-type (+/+, WT) mice (five/group) were exposed to ethylnitrosourea (ENU) or cyclophosphamide (CP). In phase I, mice were exposed by gavage to 0 or 60 mg/kg/day ENU or CP for four days and examined on test day (TD) 4, and in phase II, mice were exposed to 0, 6, 20, or 60 mg/kg/day ENU or CP for four days and evaluated on TD 36 when exposed spermatocytes matured. In phase I, mutagens were not directly cytotoxic to mature sperm. In phase II, WT mice were more sensitive to decreases in reproductive organ weights, whereas both genotypes had decreased sperm counts. Testicular histology revealed similar CP responses, but genotype-specific ENU responses (WT mice had depletion of elongating spermatids; NULL mice had late-stage spermatocyte/early stage spermatid loss). Ethylnitrosourea increased DNA strand breaks in WT mice. Thus, mice responded similarly to CP, suggesting a primarily p53-independent response, whereas the ENU response differed by zygosity, suggesting a role for p53. As DNA damage increased at higher ENU doses, compensatory repair pathways may operate in NULL mice.

Benefits of the maximum tolerated dose (MTD) and maximum tolerated concentration (MTC) concept in aquatic toxicology

There is increasing recognition of the need to identify specific sublethal effects of chemicals, such as reproductive toxicity, and specific modes of actions of the chemicals, such as interference with the endocrine system. To achieve these aims requires criteria which provide a basis to interpret study findings so as to separate these specific toxicities and modes of action from not only acute lethality per se but also from severe inanition and malaise that non-specifically compromise reproductive capacity and the response of endocrine endpoints. Mammalian toxicologists have recognized that very high dose levels are sometimes required to elicit both specific adverse effects and present the potential of non-specific "systemic toxicity". Mammalian toxicologists have developed the concept of a maximum tolerated dose (MTD) beyond which a specific toxicity or action cannot be attributed to a test substance due to the compromised state of the organism. Ecotoxicologists are now confronted by a similar challenge and must develop an analogous concept of a MTD and the respective criteria. As examples of this conundrum, we note recent developments in efforts to validate protocols for fish reproductive toxicity and endocrine screens (e.g. some chemicals originally selected as 'negatives' elicited decreases in fecundity or changes in endpoints intended to be biomarkers for endocrine modes of action). Unless analogous criteria can be developed, the potentially confounding effects of systemic toxicity may then undermine the reliable assessment of specific reproductive effects or biomarkers such as vitellogenin or spiggin. The same issue confronts other areas of aquatic toxicology (e.g., genotoxicity) and the use of aquatic animals for preclinical assessments of drugs (e.g., use of zebrafish for drug safety assessment). We propose that there are benefits to adopting the concept of an MTD for toxicology and pharmacology studies using fish and other aquatic organisms and the development of sound criteria for data interpretation when the exposure of organisms has exceeded the MTD. While the MTD approach is well established for oral, topical, inhalational or injection exposure routes in mammalian toxicology, we propose that for exposure of aquatic organisms via immersion, the term Maximum Tolerated Concentration (MTC) is more appropriate.

Transforming growth factor-beta1 null mutation causes infertility in male mice associated with testosterone deficiency and sexual dysfunction

TGFbeta1 is a multifunctional cytokine implicated in gonad and secondary sex organ development, steroidogenesis, and spermatogenesis. To determine the physiological requirement for TGFbeta1 in male reproduction, Tgfb1 null mutant mice on a Prkdc(scid) immunodeficient background were studied. TGFbeta1-deficient males did not deposit sperm or induce pseudopregnancy in females, despite an intact reproductive tract with morphologically normal penis, seminal vesicles, and testes. Serum and intratesticular testosterone and serum androstenedione were severely diminished in TGFbeta1-deficient males. Testosterone deficiency was secondary to disrupted pituitary gonadotropin secretion because serum LH and to a lesser extent serum FSH were reduced, and exogenous LH replacement with human chorionic gonadotropin (hCG) induced serum testosterone to control levels. In the majority of TGFbeta1-deficient males, spermatogenesis was normal and sperm were developmentally competent as assessed by in vitro fertilization. Analysis of sexual behavior revealed that although TGFbeta1 null males showed avid interest in females and engaged in mounting activity, intromission was infrequent and brief, and ejaculation was not attained. Administration of testosterone to adult males, even after neonatal androgenization, was ineffective in restoring sexual function; however, erectile reflexes and ejaculation could be induced by electrical stimulation. These studies demonstrate the profound effect of genetic deficiency in TGFbeta1 on male fertility, implicating this cytokine in essential roles in the hypothalamic-pituitary-gonadal axis and in testosterone-independent regulation of mating competence.

Effects of feed restriction on fertility in female rats

BACKGROUND

Feed restriction with its resultant body weight loss impacts the rodent estrous cycle; however, the manifestation of these changes in a regulatory study design has not been documented. This study reports the effects of feed restriction in the context of an FDA regulatory submission.

METHODS

Adult female rats (n = 20/group; weighing approximately 200 g each) were provided rodent chow ad lib (control) or at 20, 15, 10, or 7.5 g/rat/day (g/day) during a 2-week pre-mating phase, throughout the mating phase, and up to gestation day (GD) 7. On GD 8, all animals were provided ad lib feed until necropsy on GD 14. Estrous cyclicity, mating, and fertility parameters were evaluated.

RESULTS

Ad lib rats consumed approximately 20 and 28 g/day during the pre-mating and gestation phases, respectively. All measured fertility parameters in the 20 g/day group were similar to control values. In the 15 g/day group, body weight was reduced by 16% at 2 weeks, prolonged diestrus occurred, and fertility was compromised due to reductions in corpora lutea. Within 2 weeks, mean body weight in groups receiving < or = 10 g/day was reduced by > or = 29% compared to ad lib values, and overt changes in estrous cyclicity, mating, and fertility occurred. The 7.5 g/day group was not sustainable beyond the pre-mating phase.

CONCLUSIONS

For this study type, feed intake at < or = 50% ad lib values (< or = 10 g/day) was inadequate due to the magnitude and rapidity of body weight effects. Estrous parameters appeared slightly more sensitive than functional measures, as body weight changes of approximately 16% appeared near the threshold of changing routinely calculated estrous cycle parameters and were later associated with reduced fertility. In general, body weight differences of 10-15% by themselves were not adverse to normal reproduction (20 g/day).

Characterization of the effect of deoxynivalenol on selected male reproductive endpoints

The effect of deoxynivalenol (DON) exposure on male reproductive function was assessed in the rat. Male rats were divided into a control group (n=15 rats) and four treatment groups (0.5 mg/kg, n=15; 1.0 mg/kg, n=15; 2.5 mg/kg, n=15; and 5.0 mg/kg DON, n=16) and exposed to DON daily for 28 days via gastric intubation. Both body weight gain and the final body weight of animals in the 5.0 mg/kg dose group and feed consumption in animals in the 2.5 mg/kg and 5.0 mg/kg dose groups were significantly reduced compared to controls. Fluid consumption was not affected in any of the treated groups. Epididymal and seminal vesicle weights expressed per gram of body weight and brain weight were significantly reduced, compared to control weights, in animals from the 2.5 and 5.0 mg/kg dose groups while prostate weight expressed per gram of brain weight and body weight was significantly lower than controls only in the 5.0 mg/kg dose group. A statistically significant, dose-related decrease in homogenization resistant testicular spermatid counts, spermatid numbers, absolute cauda epididymal sperm numbers and cauda epididymal sperm numbers per gram of cauda epididymis was observed in the 5.0 mg/kg DON treatment group. Sperm tail abnormalities (broken tails) in the 5.0 mg/kg dose group were significantly higher than in the control group. Sperm swimming speed (VSL and VCL) was significantly increased only in the 2.5 mg/kg dose group. Serum FSH and LH concentrations were increased in a dose dependent manner across all treated groups while serum testosterone concentrations were decreased in a dose-related manner across all dose groups. An increase in germ cell degeneration, sperm retention and abnormal nuclear morphology was observed in the 2.5 mg/kg and 5.0 mg/kg dose groups. Treatment related effects included lesions in the non-glandular stomach, thymic lymphoid depletion and splenic hematopoiesis in the 5.0 mg/kg treatment group.

Survey of some heavy metals in sediments from vehicular service stations in Jordan and their effects on social aggression in prepubertal male mice

Vehicle services create the potential for heavy metal accumulation in the working environment. This study assessed five vehicle services, namely body repair, oil exchange, mechanical repair, tire repair, electrical repair, and washing services for three types of vehicles: airplanes, buses, and cars. The results show that there are significant increases in the total contents of Fe, Cu, Pb, Zn, Ni, Mn, and Cr in ambient dust, with Fe being the highest and Cr the lowest. The main cause of the presence of these elements is due to the metals' corrosion from vehicle sources and petroleum residue. Variations in the concentrations with the type of service and within the same service at different locations were observed. In this study, the exposure of prepubertal male mice to industrial metal salts in drinking water at a concentration of 1000 ppm for 90 days was investigated. Exposure of male mice to lead acetate significantly reduced the social aggression of the resident untreated subjects. Additionally, this treatment resulted in decreasing weights of body, testes, preputial glands, and seminal vesicles. In comparison, no such effects were seen in mice given copper chloride or manganese chloride. The results show that only lead acetate produced a pattern of responses clearly indicative of altered gonadal function.

The effect of vomitoxin (Deoxnivalenol) on testicular morphology, testicular spermatid counts and epididymal sperm counts in IL-6KO [B6129-IL6 [TmlKopf] (IL-6 gene deficient)] and WT [B6129F2 (wild type to B6129-IL6 with an intact IL-6 gene)] mice

The potential of vomitoxin (VT) to affect testicular morphology and testicular and epididymal sperm counts was assessed in three strains of mice: IL-6KO [B6129-IL6 (tmlKopf) (IL-6 gene deficient)], WT [B6129F2 (wild type to B6129-IL6 with an intact IL-6 gene)] and B6C3F1 mice in a 90-day feeding study. The treated mice received VT at a concentration of 10 ppm in their diet. The body weight of VT-treated animals was significantly reduced compared with control animals. Slight changes, not statistically significant, were observed in relative testis weight and testicular spermatid counts. Histological changes were not apparent in the testes of VT-treated animals. The diameter of the seminiferous tubules, the height of the seminiferous epithelium and the number of Sertoli cell nucleoli per cross-sectioned seminiferous tubule in the VT-treated groups were not significantly different from their respective untreated controls. The IL-6KO and B6C3F1 VT-treated mice had significantly reduced cauda epididymal weights compared with their respective controls. These changes were not attributed to decreased sperm counts and this finding suggests that VT may exert an adverse affect on the epididymis.

Assessment of aggression, sexual behavior and fertility in adult male rat following long-term ingestion of four industrial metals salts

1. The effect of long-term ingestion of the industrial metals salts, manganese sulfate, aluminum chloride, lead acetate and copper chloride was investigated on aggression, sexual behavior and fertility in male rat. Adult male rats ingested solutions of these salts along with drinking water at a concentration of 1000 p.p.m. for 12 weeks. 2. Male rat sexual behavior was suppressed after the ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride. The ingestion of solutions of these salts markedly prolonged the intromission and ejaculation latencies. Aluminum chloride and copper chloride reduced the copulatory efficiency. 3. Male rat aggression was also abolished after the ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride. The ingestion of solutions of these salts markedly suppressed lateralizations, boxing bouts, fight with stud male and ventral presenting postures. 4. Fertility was reduced in male rats ingested with lead acetate. The total number of resorptions was increased in female rats impregnated by males ingested with manganese sulfate and lead acetate. 5. Body, absolute or relative testes, seminal vesicles weights were dropped in adult male rats ingested with manganese sulfate, aluminum chloride, lead acetate and copper chloride. However, the absolute or relative preputial gland weights were not affected. Collectively, these results suggest that the long-term ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride would have adverse effects on sexual behavior, territorial aggression, fertility and the reproductive system of the adult male rat.

Formamide and dimethylformamide: reproductive assessment by continuous breeding in mice

Reproductive toxicity in Swiss mice, during chronic exposure to formamide (FORM) or dimethylformamide (DMF), was evaluated using the Reproductive Assessment by Continuous Breeding Protocols. FORM administered in drinking water at 0, 100, 350, and 750 ppm (approximately 20 to 200 mg/kg/d) reduced fertility and litter size in F0 animals without generalized toxicity at 750 ppm FORM. Crossover matings suggested that females were the affected sex. After F1 mating, FORM reduced F2 litter size, increased days to litter, reduced relative ovarian weight, and lengthened estrous cycles at 750 ppm. The No-Observed-Adverse-Effect-Level for generalized toxicity was 750 ppm for the F0 and 350 ppm for the F1 generation. Reproductive performance was normal at 350 ppm for both F0 and F1 mice. Chronic exposure to DMF in drinking water at 0, 1000, 4000, and 7000 ppm (approximately 200 to 1300 mg/kg/d) reduced fertility by the first litter at 4000 ppm, reduced body weight in F0 females at 7000 ppm, and increased liver weights at all doses in both sexes. A crossover mating at 7000 ppm identified F0 females as the affected sex. F1 postnatal survival was reduced at > or =4000 ppm DMF. F1 mating reduced F2 litter size and live pup weight at > or =1000 ppm. At necropsy, body weight of F1 males and females was reduced at > or =4000 ppm. DMF-treated pups (both F1 and F2) and F1 adults had cranial and sternebral skeletal malformations. Only DMF caused overt developmental toxicity. A No-Observed-Adverse-Effect-Level for DMF was not established.

Effect of long-term ingestion of chromium compounds on aggression, sex behavior and fertility in adult male rat

The effects of long-term ingestion of chromium chloride (trivalent compound) and potassium dichromate (hexavalent compound) was investigated on sexual behavior, aggressive behavior and fertility in male rats. Adult male rats were exposed to chromium chloride and potassium dichromate in drinking water at a concentration of 1000 ppm for 12 weeks. The exposure of male rats to chromium chloride and potassium dichromate reduced the number of mounts. The exposure of male rats to potassium dichromate increased the time to ejaculation. On the other hand, the exposure of male rats to chromium chloride and potassium dichromate increased the post ejaculatory interval. The number of animals ejaculating were reduced in chromium chloride and potassium dichromate exposed male rats. The exposure of male rats to chromium chloride and potassium dichromate decreased lateralizations, boxing bouts and fights with stud male. The exposure of male rats to chromium chloride and potassium dichromate had no effect on fertility. Testes, seminal vesicle and preputial gland weights were significantly reduced in chromium chloride- and potassium dichromate-exposed males. In conclusion, the long-term ingestion of chromium chloride and potassium dichromate would have adverse effects on sexual behavior and territorial aggression in adult male rat.

Long-term exposure of male and female mice to trivalent and hexavalent chromium compounds: effect on fertility

Sexually mature male and female mice at 50 days of age were exposed to trivalent (Chromium chloride) or hexavalent (potassium dichromate) chromium compounds in drinking water for 12 weeks. The effects of the direct chromium exposure on fertility was assessed at day 140 of age. Fertility was significantly reduced in males exposed to the trivalent chromium compound. The number of implantation sites and the number of viable fetuses was significantly reduced in females impregnated by males exposed to the hexavalent chromium compound. The number of resorptions and dead fetuses was increased in females impregnated by males exposed to trivalent and hexavalent chromium compounds. The exposure of female mice to trivalent and hexavalent chromium compounds significantly reduced the number of implantation sites and the number of viable fetuses. The number of females with resorptions was significantly increased in hexavalent chromium exposed females. The number of resorptions was increased in trivalent and hexavalent exposed females. Body, seminal vesicles and preputial gland weights were significantly reduced in males exposed to trivalent and hexavalent chromium, whereas testes weight was significantly increased in males exposed to these compounds. Furthermore, ovarian weight was significantly increased in females exposed to trivalent and hexavalent chromium, whereas uterine weight was significantly decreased in trivalent chromium exposed females. In conclusion, the ingestion of trivalent and hexavalent chromium compounds by adult male and female mice would cause adverse effects on fertility and reproduction.

Maternal toxicity and the identification of inorganic arsenic as a developmental toxicant

Assessment of the potential developmental toxicity of arsenic in humans must be based entirely on the extensive animal literature; no appropriate human data are available. Hazard identification of developmental toxicity of arsenic in animal studies is complicated by the co-occurrence of maternal and developmental toxicity when the pregnant dam is exposed to the toxicant. Current regulatory guidance requires that, when maternal and developmental toxicity occur at the same or similar doses, detailed consideration needs to be given to whether developmental toxicity is secondary to maternal toxicity or whether it represents a distinct hazard. In this review, these principles were applied to the relatively large database of animal studies available for hazard identification of inorganic arsenic as a developmental toxicant. It is concluded that maternal and developmental toxicity occur in the same dose range for this potent cytotoxicant, although differential no observed adverse effect levels can be identified depending on the endpoints used. Various evidence from the basic science literature indicates that developmental toxicity is not secondary to maternal toxicity. Current regulatory guidance falls short of defining effective approaches to resolving the difficulties posed by co-occurrence of maternal and developmental toxicity.

Modulation of toxicity by diet and dietary macronutrient restriction

Restriction of diet and macronutrients has been reported to modulate the toxicity of numerous chemical agents. Of the various forms of restriction studied, using nutritionally adequate diets, food restriction (FR) appears to be most effective, but protein restriction (PR), fat restriction (FtR), carbohydrate restriction (CbR), and excess of dietary fiber (FE) also affect toxicity and the spontaneous diseases that define the background incidence in toxicity tests. The heterogeneity of the dietary macronutrients complicates simple analysis of their effects. Additionally, the interrelationships between these various components in the complex dietary mixture often make experiments difficult to interpret. Despite these complexities, a simple model is presented, which considers the effects of dietary manipulations on the individual steps in the interaction of organism and agent, and puts the varied effects that can occur within an organism into context. Ultimately, many of the effects of dietary modulation on these steps in toxicogenesis can be considered as changing agent exposure and the biologically available dose. The effects of macronutrient restriction are discussed in terms of effects on agent at the interface of organism and toxicant, agent disposition, agent metabolism, and repair of toxicant-induced damage at the level of the genome. After illustrating the influence of these nutritional effects on the chronic bioassay, using mouse liver tumors as an example, the significance of these effects for chronic and short-term testing is discussed. Additionally, methods to address the impact of nutritional factors on toxicity testing are suggested.