Oral (drinking water) two-generation reproductive toxicity study of dibromoacetic acid (DBA) in rats

In a two-generation study of dibromoacetic acid (DBA), Crl SD rats (30 rats/sex/group/generation) were provided DBA in drinking water at 0 (reverse osmosis-deionized water), 50, 250, and 650 ppm (0, 4.4 to 11.6, 22.4 to 55.6, and 52.4 to 132.0 mg/kg/day, respectively; human intake approximates 0.1 microg/kg/day [0.0001 mg/kg/day]). Observations included viability, clinical signs, water and feed consumption, body and organ weights, histopathology, and reproductive parameters (mating, fertility, abortions, premature deliveries, durations of gestation, litter sizes, sex ratios and viabilities, maternal behaviors, reproductive organ weights, sperm parameters and implantation sites, sexual maturation). Histopathological evaluations were performed on at least 10 P and F1 rats/sex at 0 and 650 ppm (gross lesions, testes, intact epididymis; 10 F1 dams at 0, 250, and 650 ppm for primordial follicles). Developmental observations included implantations, pup numbers, sexes, viabilities, body weights, morphology, and reproductive performance. At 50 ppm and higher, both sexes and generations had increased absolute and relative liver and kidneys weights, and female rats in both generations had reduced absolute and relative adrenal weights; adrenal changes were probably associated with physiological changes in water balance. The livers and kidneys (10/sex/group/generation) had no histopathological changes. Other minimal effects at 50 ppm were reduced water consumption and a transient reduction in body weight. At 250 and 650 ppm, DBA reduced parental water consumption, body weight gains, body weights, feed consumption, and pup body weights. P and F1 generation male rats at 250 and 650 ppm had altered sperm production (retained step 19 spermatids in stages IX and X tubules sometimes associated with residual bodies) and some epididymal tubule changes (increased amounts of exfoliated spermatogenic cells/residual bodies in epididymal tubules, atrophy, and hypospermia), although inconsistently and at much lower incidences. Unilateral abnormalities of the epididymis (small or absent epididymis) at 650 ppm in four F1 generation male rats were considered reproductive tract malformations. The no-observable-adverse-effect level (NOAEL) and reproductive and developmental NOAELs for DBA were at least 50 ppm (4.5 to 11.6 mg/kg/day), 45,000 to 116,000 times the human adult exposure level. Reproductive and developmental effects did not occur in female rats exposed to DBA concentrations as high as 650 ppm. Based on the high multiples of human exposure required to produce effects in male rats, DBA should not be identified as a human reproductive or developmental risk.

Matching peptide mass spectra to EST and genomic DNA databases

The use of mass spectrometry data to search molecular sequence databases is a well-established method for protein identification. The technique can be extended to searching raw genomic sequences, providing experimental confirmation or correction of predicted coding sequences, and has the potential to identify novel genes and elucidate splicing patterns.

Interrogating the human genome using uninterpreted mass spectrometry data

The public availability of a draft assembly of the human genome has enabled us to demonstrate, for the first time, the feasibility of searching a complete, unmasked eukaryotic genome using uninterpreted mass spectrometry data. A complex LC-MS/MS data set, containing peptides from at least 22 human proteins, was searched against a comprehensive, nonidentical protein database, an expressed sequence tag (EST) database, and the International Human Genome Project draft assembly of the human genome. The results from the three searches are compared in detail, and the merits of the different databases for this application are discussed. In the case of the EST database, the UniGene index provided a method of simplifying and summarising the search results. In the case of the genomic DNA, the presence of introns prevented matching of roughly one quarter of the spectra, but the technique can provide primary experimental verification of predicted coding sequences, and has the potential to identify novel coding sequences.

Pathogenesis of male reproductive toxicity

Toxicologic disturbance of male reproductive function can occur at many sites and produce a range of effects, some primary and some secondary to the initial insult. The challenge to the toxicological pathologist is to identify the primary site of damage and provide an insight into the pathogenesis of the morphologic lesion or functional deficit. Target sites include the testis, the epididymis, the mature sperm, and the hormonal regulatory system. Detection of effects at these varied sites requires the measurement of multiple endpoints only 1 of which is histopathology, but once identified, careful microscopic examination of the early changes in lesion development can provide essential information on the probable target cell and possible mechanisms of toxicity. Chemicals that affect different cell types or specific cellular functions generally elicit predictable patterns of pathological changes that can be readily recognized. Understanding the pathogenesis, the likely reversibility and the significance of reproductive tract lesions is aided by a sound knowledge of the physiology of the testis and epididymis and, in particular, an understanding of the timing of sperm production and transport.

Two-generation reproduction toxicity studies of di-(C(7)-C(9) alkyl) phthalate and di-(C(9)-C(11) alkyl) phthalate in the rat

Di-(C(7)-C(9) alkyl) phthalate (D79P) and di-(C(9)-C(11) alkyl) phthalate (D911P), based on high-normality linear oxo-alcohols, have been assessed for their impact upon reproductive performance in Sprague-Dawley rats. Rats were continuously exposed to either D79P or D911P at dietary levels of 0%, 0.1%, 0.5%, or 1.0% over two generations. Selected F(0) offspring (F(1) generation) were exposed to the same dietary concentration of D79P or D911P as the respective F(0) animals, and were mated to produce F(1) offspring. Both D79P and D911P markedly reduced body weight gain in F(0) and F(1) adult males at the highest dose, but females were affected to a lesser extent. There was no impairment of fertility, fecundity, or development in either generation, but body weights of offspring in the 1.0% D79P and 1.0% D911P groups were slightly and transiently reduced over the weaning period. Although decreases in the weight of several organs were accounted for by depressed body weight, ovary weights were reduced in both generations exposed to 1.0% D79P, and epididymidal weights were slightly reduced in adults of both generations exposed to 1.0% D911P. However, ovarian function-assessed by the oestrus cycle and mating behaviour-and epididymidal sperm concentration, motility, and morphology were unaffected by either substance. Treatment resulted in liver changes, particularly in males, characterised by increased liver weight in young animals, histopathologic changes and reduced organ weight in mature animals, and an increase in palmitoyl CoA oxidase activity. In conclusion, neither D79P nor D911P impaired reproductive function in rats when administered in the diet at levels that induce systemic toxicity, and the NOAEL for effects on reproduction in the rat is 0.5% for both D79P and D911P.

Probability-based protein identification by searching sequence databases using mass spectrometry data

Several algorithms have been described in the literature for protein identification by searching a sequence database using mass spectrometry data. In some approaches, the experimental data are peptide molecular weights from the digestion of a protein by an enzyme. Other approaches use tandem mass spectrometry (MS/MS) data from one or more peptides. Still others combine mass data with amino acid sequence data. We present results from a new computer program, Mascot, which integrates all three types of search. The scoring algorithm is probability based, which has a number of advantages: (i) A simple rule can be used to judge whether a result is significant or not. This is particularly useful in guarding against false positives. (ii) Scores can be compared with those from other types of search, such as sequence homology. (iii) Search parameters can be readily optimised by iteration. The strengths and limitations of probability-based scoring are discussed, particularly in the context of high throughput, fully automated protein identification.

Probability-based protein identification by searching sequence databases using mass spectrometry data

Several algorithms have been described in the literature for protein identification by searching a sequence database using mass spectrometry data. In some approaches, the experimental data are peptide molecular weights from the digestion of a protein by an enzyme. Other approaches use tandem mass spectrometry (MS/MS) data from one or more peptides. Still others combine mass data with amino acid sequence data. We present results from a new computer program, Mascot, which integrates all three types of search. The scoring algorithm is probability based, which has a number of advantages: (i) A simple rule can be used to judge whether a result is significant or not. This is particularly useful in guarding against false positives. (ii) Scores can be compared with those from other types of search, such as sequence homology. (iii) Search parameters can be readily optimised by iteration. The strengths and limitations of probability-based scoring are discussed, particularly in the context of high throughput, fully automated protein identification.

Subacute and chronic toxicity studies of triethylenetetramine dihydrochloride (TJA-250) by oral administration to F-344 rats

Triethylenetetramine dihydrochloride (trientine-2HCl, TJA-250), a copper chelating agent used to treat Wilson's disease, was administered orally to male and female F-344 rats for 4 or 8 weeks at dosages of 0, 100, 350 or 1200 mg/kg/day or for 26 weeks at dosages of 50, 175 or 600 mg/kg/day. 4 or 8-week study. Two males receiving 1200 mg/kg/day died during week 8 of treatment. In males receiving 1200 mg/kg/day during weeks 5 to 8 of treatment, body weight gain and food consumption were decreased and hunched posture and thin build were observed. During week 4 or 8 of treatment urinalysis revealed, for males receiving 100 mg/kg/day or animals receiving 350 mg/kg/day or more, increased electrolyte outputs possibly due to the hydrochloride nature of trientine-2HCl, with low plasma alkaline phosphatase activities evident in animals receiving 350 or 1200 mg/kg/day. After 4 and 8 weeks, and during 8 weeks of treatment, high lung weights and bronchiolar epithelium hypertrophy and broncho-alveolar pneumonia were recorded for animals receiving 1200 mg/kg/day, and submucosal acute inflammation within the glandular region of the stomach was recorded for males receiving 350 or 1200 mg/kg/day and in all treated female groups. 26-week study. One male receiving 175 mg/kg/day and three males receiving 600 mg/kg/day died, showing lung changes. The body weight gain of animals receiving 600 mg/kg/day was slightly decreased. Blood chemistry and urinalysis examinations showed changes similar to those indicated in the 4- or 8-week study. The low plasma copper concentrations seen in males receiving 600 mg/kg/day, the slightly low liver copper concentrations found in animals receiving 600 or 175 mg/kg/day and the high urinary copper concentrations found in all treated groups, are attributed to the pharmacological action of trientine-2HCl. Histopathology revealed a dosage-related incidence and severity of focal chronic interstitial pneumonitis accompanied by fibrosis of the alveolar walls in females receiving 175 mg/kg/day or more and all treated male groups, but no significant pathological changes in the stomach. Apart from the histological changes found in the lung, all the above changes were reversible. In conclusion, the NOAEL of trientine-2HCl in this 26-week study was considered to be 50 mg/kg/day for females and less than 50 mg/kg/day for males.

Evaluation of testicular toxicity in safety evaluation studies: the appropriate use of spermatogenic staging

Toxicology of the male reproductive system has received increased interest in recent years partly fuelled by the growing reports of falling sperm counts and rising reproductive disorders in the human population. Recently revised regulatory guidelines for the safety assessment of pharmaceuticals and chemicals on reproduction and fertility have emphasized the importance of detailed histopathological examination of the testes as a sensitive method for detecting disturbances in spermatogenesis. Unfortunately this has been accompanied by a general confusion regarding a practical approach to undertaking such a detailed examination, particularly in respect to the use of spermatogenic or tubular staging to identify subtle disturbances in spermatogenesis. The ability to identify tubular stages of the spermatogenic cycle in sections of testis plus a good understanding of the spermatogenic process and its dynamics are essential in order to carry out a sensitive of testicular histopathology and to interpret the changes seen. A rational approach is required initially to detect and subsequently to characterize toxic effects to the male reproductive system. It is important that a distinction is made between these two objectives since different study designs are required and different methodology may be employed to produce the type of information or data required.

A 90-day feeding study of lupin (Lupinus angustifolius) flour spiked with lupin alkaloids in the rat

Three groups of 20 male and 20 female Sprague-Dawley rats were given diets based on lupin (Lupinus angustifolius) flour (55.4 g/100 g diet) that had been spiked to provide dietary concentrations of 250, 1050 or 5050 mg lupin alkaloids/kg diet. A control group of 20 males and 20 females received 50 mg/kg (derived from the background level of alkaloid in lupin flour). The rats were treated for a minimum of 90-98 days. A dose-related reduction in red blood cell count and haematocrit (HCT) occurred in both sexes after 45 days, and the mean cell volume (MCV) was decreased in all the male treatment groups. The reductions in HCT and MCV persisted in the males until termination of the study when decreased haemoglobin levels were also observed in the top-dose males. The relative liver weights of female rats showed a dose-related increase. Altered foci of liver parenchymal cells were seen in five females receiving dietary levels of 5050 mg/kg, in one female fed 250 mg/kg and in one male from each of the 250 mg/kg and 1050 mg/kg treatment groups. No foci were seen in the control group. Basophilic foci are uncommon in young rats suggesting that the low incidence in this study is compound related.

Comparison of urinary creatine with other biomarkers for the detection of 2-methoxyethanol-induced testicular damage

Abstract This study has compared different biomarkers of testicular damage, in particular evaluating urinary creatine as a non-invasive marker. Male rats were exposed to various doses of 2-methoxyethanol, a known testicular toxicant. Pathological damage, testis weight, urinary creatine and creatinine, serum lactate dehydrogenase, isozyme C4 (LDH-C4), and serum testosterone were determined. 2-Methoxyethanol caused dose-dependent pathological damage to the testes which was detectable at the lowest dose (100 mg kg(-1)). Urinary creatine excretion was significantly raised at all doses but testis weight was only significantly decreased at the highest two doses (500, 750 mg kg(-1)). Serum testosterone was only significantly decreased at 500 mg kg(-1) and LDH-C4 was not significantly increased at any dose. Therefore urinary creatine was the most sensitive marker of 2-methoxethanol-induced testicular damage and dysfunction.

Urinary creatine profiles after administration of cell-specific testicular toxicants to the rat

Cell-specific testicular toxicants have been used to examine the distribution of creatine within the rat testis, and to examine the potential use of creatinuria as a non-invasive indicator of testicular damage. Groups of rats were administered single doses of various toxicants: a germ cell toxicant (methoxyacetic acid, MAA), one of two Sertoli cell toxicants (di-n-pentyl phthalate, DPP or 1,3-dinitrobenzene, 1,3-DNB), or a Leydig cell toxicant (ethane-1,2-dimethane sulphonate, EDS). Urinary creatine and creatinine levels were monitored in 24 h periods over the following 48 h, after which time the testes were removed, weighed and, after processing, sections were examined by light microscopy. All four treatments resulted in reductions in relative testis weight (RTW) and produced morphological changes similar to those which have been previously reported. In addition, MAA, DPP and 1,3-DNB all caused significant elevations in urinary creatine excretion and the urinary creatine:creatinine ratio (Cr/Crn) within 24 h. EDS had no such effect. We conclude that creatine is associated with the cells of the seminiferous epithelium, and that elevated urinary excretion of creatine may serve as a non-invasive marker for damage to these cells in vivo.

A 28-day feeding study with ethyl acetoacetate in rats

Ethyl acetoacetate encapsulated in gum arabic was administered in rodent diet for a minimum of 28 consecutive days to groups of 16 male and 16 female rats (Sprague-Dawley strain) at levels of approximately 100, 300 and 1000 mg/kg body weight/day. A further group of 16 male and 16 female rats was given rodent diet containing gum arabic as a control. The administration of ethyl acetoacetate in the diet did not adversely affect the growth or general health of the animals or their food intakes. None of the minor variations observed in the haematology, serum chemical analyses or urine analyses are considered to be indicative of a treatment-related toxic effect. Caecal enlargement was seen in male rats treated with the top dose of ethyl acetoacetate, but this was accompanied by a normal histopathology. Few histopathological abnormalities were observed. Proteinaceous casts were found in the bladder of approximately half the male rats given 1000 mg ethyl acetoacetate/kg, and nephrocalcinosis was a common occurrence in female rats in this dose group. Renal function was unimpaired in treated male and female rats, and the histopathological findings are common in the strain of rats chosen for this study. Although the caecal enlargement and the changes in kidney and bladder of rats given 1000 mg ethyl acetoacetate/kg are noted, it is considered that ethyl acetoacetate did not produce treatment-related adverse effects in rats during this study.

A 28-day feeding study with methyl isoeugenol in rats

Methyl isoeugenol was administered in rodent diet for a minimum of 28 consecutive days to groups of 16 male and 16 female rats (Sprague-Dawley strain) at levels of approximately 30, 100 and 300 mg/kg body weight/day. A further group of 16 male and 16 female rats was given the rodent diet as a control. The administration of methyl isoeugenol in the diet did not adversely affect the growth or general health of the animals or their food intakes. Although high dose animals of both sexes had increased lymphocyte and total white blood cell counts, these are not considered, in isolation, to be an adverse effect of treatment. None of the minor variations observed in the serum chemical analyses or urine analyses is considered to be indicative of a treatment-related toxic effect. An increase in liver weight, adjusted for body weight, was seen in male and female rats receiving 300 mg methyl isoeugenol/kg body weight. Few histopathological abnormalities were observed. Although the incidence of kidney and Harderian gland lesions was higher for high dose animals compared with the controls, the lesions are of a type that occurs spontaneously and are thus not considered to be attributable to treatment with methyl isoeugenol. While the increased liver weight and white blood cell counts of rats given 300 mg methyl isoeugenol/kg body weight may represent effects of treatment, it is not considered that there is any reason to regard these as adverse effects.

Di-n-pentyl phthalate-induced inflammatory changes in the rat testis are accompanied by local production of a novel lymphocyte activating factor

Phthalate esters (PAE) are plasticizers in polyvinyl chloride plastics used, for example, in package material for medical solutions. PAE exposure is associated with testicular damage that primarily affects Sertoli cells, and is concomitant with leukocyte infiltration into the testicular interstitium. We have demonstrated that the rat testis constitutively produces a lymphocyte activating factor (LAF) resembling interleukin-1 alpha, and originating from Sertoli cells. The testicular interleukin-1-like factor (tIL-1) has a relative molecular mass (Mr) of 17,000 (17 k) and an isoelectric point (pI) of 5.7. In the present study we have measured testicular LAF activity after exposure to di-n-pentyl phthalate (DPP) in 40-day-old rats. We found a large increase in LAF bioactivity which was evident already 3 h after a single oral dose of DPP. The increase was maximal 9-12 h after exposure, and had decreased toward the control level at 24 h. The increased activity was found to be at least partly due to the induction of a novel LAF with Mr 38,000 and pI 4.5. Morphological examination confirmed earlier results with an interstitial leukocyte infiltration 6 h after DPP exposure. The identity of the novel LAF and its functional relation to testicular inflammation remain to be established.

Studies on the relationship between acute testicular damage and urinary and plasma creatine concentration

A single dose of cadmium chloride (3.23 mumol Cd2+/kg) causing acute testicular damage in male rats also caused significant creatinuria and creatinaemia at 48 h after dosing. Doses of cadmium which did not cause testicular necrosis did not cause creatinuria or creatinaemia. Surgical ligation of the pampiniform plexus also caused ischaemic necrosis of the testis and this was followed by significant creatinuria and creatinaemia. However, neither orchidectomy followed by a toxic dose of cadmium, orchidectomy alone nor sham operation caused significant creatinuria or creatinaemia. Cadmium dosing induced a temporary loss of body weight which was less than that caused by food restriction. Food restriction did not cause significant creatinuria but did cause significant creatinaemia. These data suggest that the creatine is derived from the damaged testis and that measurement of urinary creatine may be a useful non-invasive means of detecting acute testicular damage caused by exposure to chemicals or mechanical impairment of blood flow.

The morphogenesis of cyclohexylamine-induced testicular atrophy in the rat: in vivo and in vitro studies

Male Wistar strain rats were fed a diet providing an intake of 0 or 400 mg cyclohexylamine (CHA)/kg body weight/day for 1, 3, 7, 9, or 13 weeks. At the end of the appropriate feeding period the rats were perfused-fixed with Karnovsky's fixative. The weights of the fixed testes were recorded and the testes, epididymides, and spermatic cord were sampled and processed into methacrylate resin. Histopathological examination of the testes showed changes after 3 weeks of CHA administration. The most frequent and consistent lesion consisted of a focal, basal vacuolation of the Sertoli cell cytoplasm associated with the local loss of spermatocytes and spermatogonia. After a 7-week administration, the Sertoli cell vacuolation was extensive, while the germ cell population showed mild to moderate degeneration and depletion. After longer periods of treatment the lesion was more severe and affected a greater number of tubules leading to general disruption of the germinal epithelium. Cocultures of Sertoli and germ cells were prepared from the testes of Wistar strain rats and exposed to (CHA) or its metabolite 4-aminocyclohexanol (4ACH) at concentrations ranging from 0.1 to 10 mM for periods of 24-72 hr. The cultures were fixed, stained, and examined by light microscopy. Cultures exposed to CHA or 4ACH showed morphological changes comparable with those seen in vivo. Sertoli cell vacuolation was the earliest change with progressive germ cell degeneration and exfoliation from the Sertoli cell monolayer. At equimolar concentrations, CHA produced more marked changes than 4ACH. These results suggest that CHA itself acts directly on the testis and that its primary cellular target is the Sertoli cell.

The metabolism and testicular toxicity of cyclohexylamine in rats and mice during chronic dietary administration

Cyclohexylamine hydrochloride has been given in the diet to mice and to Wistar and DA rats for 13 weeks, to provide a constant intake of 400 mg of the base/kg/day. Significantly decreased food intake and body weight gain were found in both strains of rats but not mice. The metabolism of [14C]cyclohexylamine was widely different in Wistar and DA rats and in rats and mice, and these differences were not altered appreciably by chronic intake for 13 weeks. The differences in metabolism resulted in marked and persistent differences in the concentrations of the hydroxylated metabolites in the plasma and testes of treated animals with Wistar much greater than DA much greater than mice. After 7 and 13 weeks testicular atrophy was demonstrated in both strains of rats given cyclohexylamine diet by a decrease in organ weight and by histological changes. DA rats appeared more sensitive to testicular toxicity from cyclohexylamine than Wistar rats, while mice showed no evidence of testicular damage. These data show that the development of testicular toxicity is not related to the extent of hydroxylation. The concentrations of cyclohexylamine in the plasma and testes of the treated animals were lower in mice than in either strain of rats despite a similar daily intake. This suggests that species differences in pharmacokinetics may contribute to the apparent difference in sensitivity to testicular toxicity.

Three-generation toxicity study of rats ingesting Green S in the diet

Green S was fed to rats of both sexes, over three generations, at dietary concentrations designed to provide daily intakes of 0, 50, 500 or 1000 mg Green S/kg body weight. At each generation, treated groups each consisted of 36 males and 36 females with 60 of each sex as controls. The F0 generation first received Green S as weanlings, but succeeding generations were exposed throughout life, including in utero, as treatment continued during gestation and lactation. There were no adverse effects of treatment on body-weight gain, food and water consumption or on the general condition of the animals. Green-coloured faeces were produced by all animals exposed to the colouring and pale green coloration of urine or the bladder was seen in a few animals at autopsy. The post-mortem examinations and organ weights of animals receiving up to 500 mg Green S/kg/day showed no adverse effects of treatment. At 1000 mg/kg/day findings related to treatment were increased spleen weight (both sexes) and increased kidney weight (male), but relevant histopathological changes were not seen in either of these organs. Caecal enlargement was the most consistent finding in animals receiving 500 or 1000 mg Green S/kg/day, but this was not considered to be a toxic effect. Reproductive performance and intra-uterine development were not affected by treatment despite green colouring being visible in the amniotic sacs of foetuses from dams given 500 or 1000 mg Green S/kg/day. Small differences in the degree of skeletal ossification of foetuses from F2 generation dams were not related to treatment. A slightly premature eruption of the incisors during postnatal development of treated animals was not considered to be an adverse effect. It is concluded that the no-untoward-effect level in this study is 500 mg Green S/kg body weight/day.

Long-term toxicity study of Green S in mice

Groups of 105 (control) or 65 (treated) female CD-1 mice were mated one to one with equal numbers of males after both sexes had received diets containing 0 (control), 0.033, 0.33 or 0.66% Green S for 9 wk. The number of animals pregnant, the number of young born and the number surviving were similar in all groups. One male and one female from each litter were used to provide groups of 85 (control) or 50 (treated) mice of each sex for the long-term study. Treatment with Green S continued throughout pregnancy and rearing. Body weight and condition were regularly monitored for each animal throughout the study. Blood was examined from groups of 20 mice from the control and highest treatment groups at wk 14, 28 and 51 and from all survivors at the end of the study. A post-mortem examination was carried out on all animals in the long-term study and a full range of tissues was preserved and examined by light microscopy. Organ weights were recorded at the autopsy of all mice reaching the end of the study. No effects that could be attributed to treatment were seen in any of the observations. The no-untoward-effect level of Green S fed to mice for 2 yr is concluded to be 0.66% of the diet, equivalent to intakes of approximately 530 and 660 mg/kg body weight/day in males and females, respectively.

The ultrastructural effects of di-n-pentyl phthalate on the testis of the mature rat

A sequential morphological study has been carried out to examine the ultrastructural effects of di-n-pentyl phthalate (DPP) on the mature rat testis. A single oral dose of 2.2 g DPP/kg body wt was administered, and testes, perfuse-fixed 3-48 hr after dosing, were examined by transmission electron microscopy. By 3 hr, rarefaction of the basal Sertoli cell cytoplasm was seen and the basal plasma membranes separating adjacent Sertoli cells were thrown into a series of convoluted profiles with the appearance of interdigitating cell processes. The subjacent ectoplasmic specializations that normally face these membranes were disrupted, and by 12 hr the inter-Sertoli junctions showed numerous membrane discontinuities. The lateral processes of Sertoli cell cytoplasm, which separate germ cells, showed retraction and fragmentation, resulting in direct contact between adjacent germ cells or the isolation of germ cells unapposed by Sertoli cell plasma membrane. In addition, the ectoplasmic specializations associated with Sertoli-spermatid and Sertoli-pachytene spermatocyte junctions were often disrupted or absent. The mitochondria in the Sertoli cells were enlarged and, in some tubules, increased in number. The changes seen were restricted to tubules in the successive stages XI-XIV, I, and II of the spermatogenic cycle. Elongating spermatids (steps 12-15) showed cytoplasmic condensation and vacuolation by 12 hr and were necrotic by 24 hr. A small proportion of zygotene and early pachytene spermatocytes showed necrosis by 24 hr after dosing. By 48 hr, the cytoplasmic rarefaction and convoluted plasma membranes had regressed and ectroplasmic specializations had reformed along Sertoli-Sertoli junctions.

Effect of ethylene glycol monomethyl ether on spermatogenesis, dominant lethality, and F1 abnormalities in the rat and the mouse after treatment of F0 males

Adult male CD rats and CD-1 mice were given a single oral dose of ethylene glycol monomethyl ether (EGM) at 0, 500, 750, 1,000, or 1500 mg/kg. Groups of 10 were killed at weekly intervals after dosing for analysis of sperm counts and morphology or testicular histology; further groups of 10 were sequentially mated to pairs of virgin females to test for dominant lethality or gross foetal malformations in the F1 generation (F1 abnormalities). EGM was found to deplete the spermatocytes of both species severely, principally pachytene cells, but with other stages affected with increasing dose. A delay in the progression of spermatogenesis may account for a discrepancy between the apparent stage-specificity of damage deduced from lowered sperm counts and that observed histologically. In the rat, morphological abnormalities were observed in sperm that had been exposed as spermatocytes; in the mouse, however, the sensitive cells were the late spermatocytes and early spermatids. In all these parameters there was an indication of a dose-response relationship in both rats and mice. In the mating studies EGM induced a dose-related decrease in fertility 5 weeks after dosing in the rat, but complete sterility in all but the lowest dose after 6 weeks. In contrast, EGM had no effect on the reproductive capacity of the mouse. There was no statistically significant evidence for the induction of dominant lethal mutations or F1 abnormalities in either species. A single oral dose of cyclophosphamide (CTX) at 100 mg/kg induced a significant increase in dominant lethality in both species. CTX reduced the number of total implants in the rat and induced a nonsignificant increase in the number of abnormal offspring sired by treated male mice.

An ultrastructural study of ethylene glycol monomethyl ether-induced spermatocyte injury in the rat

Previous studies have shown that administration of ethylene glycol monomethyl ether (EGM) to the rat results in testicular damage with the spermatocyte being the primary cellular site for toxicity. An ultrastructural study has now been carried out to characterize the early subcellular changes following a single dose of 250 or 500 mg EGM/kg body weight. At 12 and 18 hr after dosing, large membrane bound intracellular vacuoles filled with flocculent or granular material were observed in the basal region of the tubules. These mostly appeared to originate as rarefaction and swelling of Sertoli cell processes. Necrosis of spermatocytes was evident at 12 hr but the process of cell death was rapid with cells either appearing normal or in an advanced state of necrosis. Many of the spermatocytes which appeared otherwise normal, showed areas of plasma membrane dissolution, a change which was also seen affecting the facing Sertoli cell plasma membrane resulting in continuity of the cytoplasm between the two cells. This membrane change was seen in the absence of any other morphological abnormality in the affected spermatocyte, although slight mitochondrial condensation was sometimes also present. By 24 hr after dosing, most of the spermatocytes in the spermatogenic stages which had shown the earlier membrane changes, had become necrotic while Sertoli cell vacuolation had largely regressed. Although the membrane dissolution was an early and specific effect, it is regarded as part of the phagocytic response of the surrounding Sertoli cell. It is suggested that the vacuolar changes in the Sertoli cell may be causally associated with spermatocyte injury.

A quantitative study of stage-specific spermatocyte damage following administration of ethylene glycol monomethyl ether in the rat

A quantitative study has been carried out to characterize the stage susceptibility of the spermatocyte to ethylene glycol monomethyl ether (EGM) toxicity. EGM was administered as a single oral dose of 250 mg/kg body wt and rats were examined at time periods after dosing. The number of spermatocytes and round spermatids in tubules at each stage of spermatogenesis was counted. A sharp transition in susceptibility was observed between zygotene spermatocytes in stage XIV which showed no effect and pachytene spermatocytes in stage I which showed death or depletion of 70% of its population after 1 day. A similar transition was seen between dividing spermatocytes and step 1 spermatids, the latter being unaffected. There was a gradual reduction in susceptibility toward midpachytene such that cells in stages VII-XI showed no effect. Analysis of later time periods revealed no effect on spermatogonia or prepachytene spermatocytes but did indicate that midpachytene spermatocytes underwent delayed cell death after further progression through the cycle. In a separate sequential morphological study of early changes, the earliest signs of necrosis were seen 12 hr after dosing and were restricted to spermatocytes in stages V, XI, and XII. Cell death then progressed in a wave-like manner through stages XIII and XIV finally reaching stage I, 24 hr after dosing.

The role of metabolism in 2-methoxyethanol-induced testicular toxicity

The role of metabolism in 2-methoxyethanol (ME)-induced testicular toxicity has been investigated with Sprague-Dawley rats. Following administration of [14C]ME (250 mg/kg, ip) to a group of animals, there was evidence of testicular damage, identified as depletion of the spermatocyte population. Radioactivity detected in urine over 48 hr after treatment accounted for 55% of the dose. The major urinary metabolites were identified by HPLC and isotope dilution analysis, as methoxyacetic acid (MAA) and methoxyacetylglycine (accounting for 50 to 60% and 18 to 25%, respectively, of urinary radioactivity). Analysis of plasma revealed a rapid conversion of ME to MAA (t1/2 for disappearance of ME = 0.6 +/- 0.03 hr) and gradual clearance of radioactivity (t1/2 = 19.7 +/- 2.3 hr). Pretreatment of animals with pyrazole (400 mg/kg, ip) 1 hr prior to [14C]ME dosing gave complete protection against the testicular toxicity of ME. Radioactivity detected in the urine from the pyrazole-pretreated groups over 48 hr (18%) was significantly lower than in the ME-only group. The major radioactive peak co-chromatographed with ME (30 to 36% of the total urinary radioactivity). MAA and methoxyacetylglycine were not major metabolites. Analysis of plasma revealed almost complete inhibition of the conversion of ME to MAA (t1/2 for disappearance of ME = 42.6 +/- 5.6 hr, clearance of radioactivity t1/2 = 51.0 +/- 7.8 hr). The results demonstrate that metabolic activation is required for 2-methoxyethanol to exert toxicity to the male reproductive system.

Studies on the toxicity of some glycol ethers and alkoxyacetic acids in primary testicular cell cultures

Primary mixed cultures of Sertoli and germ cells were prepared from testes of immature rats and their response to the known testicular toxicants ethylene glycol monomethyl ether (EGM) and ethylene glycol monoethyl ether (EGE) was studied. Neither EGM nor EGE produced any morphological evidence of toxicity when added to the culture medium at up to 50 mM for 72 hr. In contrast, their metabolites methoxyacetic acid (MAA) and ethoxyacetic acid (EAA) at 2 to 10 mM for 24 to 72 hr caused degeneration of the pachytene and dividing spermatocytes, the target cells of the parent ethers in vivo. As in vivo, earlier spermatocytes, spermatogonia, and Sertoli cells appeared unaffected. EAA was less potent than MAA whereas n-propoxy- and n-butoxyacetic acid, and methoxyacetylglycine, a further metabolite of MAA, produced no morphological changes under these conditions. The same order of toxicity was observed in concurrent studies with the four acids in rats. In culture, the severity of the morphological changes was paralleled by decreases in the activity of carnitine acetyltransferase and lactate dehydrogenase-X in the attached germ cell fraction. Analysis of culture medium provided no evidence for the conversion of EGM to MAA or other metabolites or for the further metabolism of MAA. The close correspondence between the testicular toxicity of alkoxyacetic acids in culture and in vivo suggests a similar mode of action in both cases and points to the potential value of these cultures for mechanistic studies and for screening purposes. The results also emphasize the role of metabolism in the testicular toxicity of glycol ethers and indicate that MAA is an active metabolite of EGM.

Testicular toxicity produced by ethylene glycol monomethyl and monoethyl ethers in the rat

Ethylene glycol monomethyl ether (EGME) and ethylene glycol monoethyl ether (EGEE) were administered orally to young male rats at doses varying from 50 to 500 mg/kg/day and 250 to 1000 mg/kg/day for EGME and EGEE, respectively, for 11 days. At sequential times animals were killed and testicular histology examined. The initial and major site of damage following EGME treatment was restricted to the primary spermatocytes undergoing postzygotene meiotic maturation and division. EGEE produced damage of an identical nature, but a larger dose was required to elicit equivalent severity (500 mg EGEE/kg being approximately equivalent to 100 mg EGME/kg). Additionally, within the spermatocyte population, differential sensitivity was observed depending on the precise stage of meiotic maturation: dividing (stage XIV) and early pachytene (stages I-II) greater than late pachytene (stages VIII-XIII) greater than mid-pachytene (stages III-VII). Equivalent doses of methoxyacetic acid (MAA) and ethoxyacetic acid (EAA) gave injury similar to the corresponding glycol ether. When animals were pretreated with inhibitors of alcohol metabolism followed by a testicular toxic dose of EGME (500 mg/kg), an inhibitor of alcohol dehydrogenase (pyrazole) offered complete protection. Pretreatment with the aldehyde dehydrogenase inhibitors disulfiram or pargyline did not ameliorate the testicular toxicity of EGME. In mixed cultures of Sertoli-germ cells, MAA and not EGME produced effects on spermatocytes analogous to that seen in vivo, at concentrations approximately equivalent to steady-state plasma levels after a single oral dose of EGME (500 mg/kg). It would seem likely that a metabolite (MAA or possibly methoxyacetaldehyde) and not EGME is responsible for the production of testicular damage.

The morphological development of glycol ether-induced testicular atrophy in the rat

The testicular effects of daily oral dosing with two glycol ethers--either ethylene glycol monomethyl ether (EGM) or monoethyl ether (EGE) were studied in the prepubertal rat by histological examination of the testes. Over the 11-day dosing period studied, EGM was found to produce testicular damage at dose levels of and in excess of 100 mg/kg/day with a no-effect level at 250 mg/kg/day. The findings at sequential time intervals throughout the dosing period indicated that primary spermatocytes undergoing pachytene development constituted the initial and major site of morphological damage. Within this population, differential sensitivity was demonstrated depending on the precise stage of meiotic maturation. A consistent order of spermatocyte susceptibility emerged from the results: dividing spermatocytes (Stage XIV) greater than early-pachytene spermatocytes (Stages I-III) greater than late-pachytene spermatocytes (Stages IX-XIII) greater than midpachytene spermatocytes (Stages IV-VIII). Leptotene/zygotene spermatocytes and Step 1 spermatids also showed degenerative changes but only after prolonged dosing at high-dose levels. The significance of the findings with respect to mechanisms of cellular toxicity in the testis is discussed.

Testicular toxicity of ethylene glycol monomethyl and monoethyl ethers in the rat

Ethylene glycol monomethyl (EGM) and monoethyl (EGE) ethers were administered po to rats at dosages varying from 50 to 500 mg/kg body weight/day for EGM and 250 to 1000 mg/kg body weight/day EGE for 11 days. First evidence of testicular damage following EGM treatment was observed 24 hr after a single dose of 100 mg/kg body weight when the lesion appeared localized in the primary spermatocyte. At 16 hr after a single dose of 500 mg/kg, mitochondrial damage was one of the first subcellular changes to be demonstrated. Treatment of animals with EGE resulted in a similar lesion; however, to obtain damage of equivalent severity, a larger dosage for a longer period was required. In limited studies with 2-methoxy- and 2-ethoxyacetic acids (putative metabolites of EGM and EGE, respectively), using equimolar doses to their parent compounds (500 mg EGM or EGE/kg for 4 or 11 days, respectively) gave damage of equivalent severity to the corresponding glycol ether. After dosing animals with 500 mg EGM/kg body weight for 4 days, the testes recovered weight, and the majority of tubules recovered their spermatogenic potential within one full maturation cycle. The recovery study also indicated a possible effect on the spermatogonia in a small number of tubules although no morphological abnormalities to this cell type could be observed. No effect levels over the 11-day treatment period were 50 and 250 mg/kg body weight/day for EGM and EGE, respectively.

The morphological development of di-N-pentyl phthalate induced testicular atrophy in the rat

Prepubertal rats treated orally with di-n-pentyl phthalate at 2.2 g/kg body weight were killed at 1, 3, 6 and 24 hr following a single dose, and after 2, 3 and 4 days of repeated daily dosing. At 3 hr Sertoli cells in a proportion of the seminiferous tubules showed vacuolation of the perinuclear smooth endoplasmic reticulum with an associated inward displacement of germinal cells. By 6 hr the vacuolation had extended to the apical cytoplasm and was evident in most tubules. Early degenerative changes were also apparent in spermatocytes and spermatids and were accompanied by an acute interstitial inflammatory infiltrate. By 24 hr, germinal cell degeneration was extensive with desquamation and general disorganisation of cell layers within the epithelium, but the interstitial inflammatory infiltrate had declined. Mitochondrial succinic dehydrogenase activity in Sertoli cells was reduced at 3 and 6 hr and absent by 24 hr. In germinal cells it was unaffected at 3 and 6 hr but absent by 24 hr. Two, three and four days of daily phthalate treatment resulted in a gradual depletion of germinal cells from all tubules, leaving a Sertoli cell matrix containing a few necrotic spermatocytes and occasional normal spermatogonia. The significance of the early Sertoli cell changes is discussed.

Prostacyclin (PGI2) effects on anterior pituitary hormones in the rat in vivo

Intravenous injection of 600 microgram PGE2 or PGI2 significantly increased serum LH and prolactin levels in estradiol treated ovariectomized rats. There was no effect on serum FSH concentration. PGE2 and PGI2 stimulated LH release in a non-dose dependent manner, while prolactin levels were positively correlated with the dose administered following PGI2 treatment. 6-keto-PGF1 alpha at a comparable dose had no effect on pituitary hormone levels. Subcutaneous administration of 1 mg/kg or 60 mg/kg PGI2 for seven days significantly depressed serum LH level both in male and female rats. These doses had no effect on serum FSH or prolactin levels.

Wholebody autoradiography: a beta-radioluminescence method for detecting tritium

A method of increasing the sensitivity of X-ray film for the wholebody autoradiography of tritiated compounds is described. Thirty micrometre sections are sprayed with a scintillator, Diphenyl oxazole (PPO) and exposed to light sensitive (screen) X-ray film at -70 degrees C. The method permits a substantial reduction in the required dose of tritium and of the period of exposure of tissue sections.