Pituitary function following treatment with reproductive toxins.

Appropriate regulation of reproductive processes are dependent upon the integrity of pituitary function. In this selected review, we evaluate the evidence that certain environmental compounds exert their effect on reproductive function via a direct action on the pituitary gland. We also discuss examples of changes in pituitary hormone secretion that occur in response to changes in neuronal or gonadal control of the pituitary. A limited number of studies suggest that measures of pituitary hormone secretion provide an early and sensitive measure of a compound's potential effects on the reproductive system. However, the most striking aspect of this area is the sparse and inconsistent information describing pituitary function following exposure to environmental pollutants.

Effects of the benomyl metabolite, carbendazim, on the hypothalamic-pituitary reproductive axis in the male rat.

Carbendazim (MBC), the bioactive metabolite of the fungicide benomyl, has been reported to induce a number of testicular alterations in male rats. Since it is possible that extragonadal changes contribute to the appearance of such effects, the present study focused on the presence of concurrent endocrine changes in the hypothalamic and pituitary components of the brain-pituitary-testicular axis. Subchronic administration of MBC (50, 100, 200 or 400 mg/kg) was found to cause a dose-related elevation in serum follicle stimulating hormone (FSH) and pituitary luteinizing hormone (LH). Values for prolactin and thyroid-stimulating hormone remained unchanged. No statistical differences in gonadotropin-releasing hormone concentrations were present in mediobasal hypothalamus, although an elevation in anterior hypothalamic values was found at the low dose, followed by a dose-related decline. These findings demonstrate that previously reported gonadal differences following subchronic exposure to carbendazim are accompanied by alterations elsewhere in the reproductive system which appear to involve both changes in Sertoli cell-pituitary feedback signals and direct effects of the compound on the central nervous system.

Effect of inhaled methanol on pituitary and testicular hormones in chamber acclimated and non-acclimated rats.

Two experiments were conducted in which the acute effects of inhaled methanol on serum hormones associated with reproductive function in the male rat were evaluated. In the first experiment, rats exposed to methanol (0, 200, 5000 and 10,000 ppm) for 6 h were killed at the end of the exposure period (6 h) or the following morning (24 h). Also, because the process of exposure itself could modify neuroendocrine function, the effect of the handling associated with placing the rat in the exposure chamber was evaluated further by dividing the exposed animals into acclimated (2 weeks of prior handling) and non-acclimated groups. At 6 h, an effect of prior handling was noted in the sham-exposed rats, with serum luteinizing hormone (LH) of the non-acclimated group being greater than that of the acclimated group. Serum LH concentrations were altered by methanol exposure, but the direction of change and the exposure level at which an effect was noted differed between the acclimated and non-acclimated rats. Methanol (5000 ppm) reduced serum LH in the non-acclimated animals, while 10,000 ppm increased LH in the acclimated rats. Follicle stimulating hormone (FSH) and testosterone were unchanged by methanol in rats killed at 6 h. Thus, this experiment did not confirm earlier reports that exposure to 200 ppm for 6 h reduced serum testosterone. At 24 h, an effect of prior handling was still present in the hormonal measures, with serum and interstitial fluid testosterone concentrations being greater in the non-acclimated rats. Also, there was a dose x handling interaction with methanol exposure inducing an increase in serum testosterone in the non-acclimated rats (up to 5000 ppm) and a decrease in the acclimated rats (up to 10,000 ppm). In the second experiment, groups of acclimated and non-acclimated rats were exposed to 0 or 5000 ppm methanol for 1, 2 and 6 h and killed immediately after removal from the chamber. Serum LH, testosterone and FSH values were not different in sham- vs methanol-exposed rats at any time point. As in experiment 1, an effect of prior handling was noted. In general, the concentrations of these hormones and serum prolactin in the non-acclimated rats were greater than those observed for acclimated rats. Methanol exposure resulted in increased prolactin concentrations under both handling conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of strontium in environmental media.

A procedure is described for the determination of strontium in natural materials by name photometry. An alkaline fusion of the ashed sample followed by dissolution in dilute acid gives a preliminary separation. Further separation of strontium is obtained by sorption on Dowex-50 resin from an EDTA solution at pH 5.1 followed by elution of the alkali metals with 0.5M hydrochloric acid, and of the strontium with 3M hydrochloric acid. The emission line at 460.7 mmu; is used and the intensity enhanced by the addition of s-butanol to the solution.

Effects of methyl benzimidazolecarbamate during early pregnancy in the rat.

Methyl 2-benzimidizolecarbamate (MBC), an agricultural fungicide, and its parent compound benomyl have adverse reproductive effects on male rats and exhibit embryotoxicity, including teratogenicity, when administered to rats during mid to late pregnancy. This study was designed to assess potential maternal effects of MBC during early pregnancy, to distinguish maternal from embryotoxic effects of the chemical, and to differentiate between early pregnancy failure and late embryonic loss. MBC was administered to rats by gavage at 0, 25, 50, 100, 200, 400, and 1000 mg/kg/day during Days 1 through 8 of pregnancy (Day 0 = sperm positive). A range of maternal and embryonic parameters was assessed following euthanasia on Day 9, including the number of implantation sites, body weight gain, uterine weight, implantation site size, and serum ovarian and pituitary hormones. In a separate experiment, pseudopregnant rats were administered 0 or 400 mg/kg/day MBC during Days 1-8, received bilateral uterine decidual induction on Day 4, and were killed on Day 9 at which time the decidual cell response was evaluated as a measure of uterine competency. When dosages of up to 400 mg/kg/day of MBC were administered during early pregnancy, the chemical had no significant effect on any measured parameter but a trend toward increased resorptions was evident. The 1000 mg/kg/day dosage of MBC produced reductions in body weight gain, implantation site weight, and serum LH and an increase in serum estradiol. When administered during pseudopregnancy, 400 mg/kg/day MBC partially reduced uterine decidual growth but affected no other parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute exposure to boric acid on the male reproductive system of the rat.

Adult male rats were dosed orally on d 0 with 0 or 2000 mg/kg of boric acid and killed on posttreatment d 2, 14, 28, and 57, or dosed with 0, 250, 500, 1000, or 2000 mg/kg of boric acid and killed on posttreatment d 14. At d 14, atypical structures that appeared to be enlarged irregular cytoplasmic lobes of Step 19 spermatids were observed in Stage VIII seminiferous tubules of rats dosed with 1000 and 2000 mg/kg. Abnormal retention of Step 19 spermatids and residual bodies was also observed in Stage IX-XIII tubules of these rats. The retained spermatids and residual bodies were seen in both the luminal and basal regions of the epithelium. A substantial increase in the testicular sperm head count occurred in animals dosed with 2000 mg/kg. Abnormal caput epididymal sperm morphology and reduced caput epididymal sperm reserves were observed at 1000 mg/kg and higher. Serum LH, FSH, TSH, and prolactin values were not affected at any dosage. At d 28, rats dosed with 2000 mg/kg exhibited continued retention of Step 19 spermatids into Stage X, abnormal caput and cauda sperm morphology, and decreased percentages of motile cauda spermatozoa with reduced straight-line swimming velocities. By d 57 substantial recovery was apparent; some retention of Step 19 spermatids into Stage X tubules was still present in two out of six rats but the sperm parameters were comparable to controls. The study indicated that acute oral exposure to boric acid adversely affected spermiation and sperm quality in the adult male rat. At the dosages used the effects appeared reversible. The no-effect level was 500 mg/kg.

Age-dependent changes in gastrointestinal transport and retention of particulate manganese oxide in the rat.

Translocation of inhaled particulates from the nasopharynx and upper tracheobronchial area to the gastrointestinal tract is a major route of exposure for particles with a mass median diameter of greater than 1 micron. Previous studies in this laboratory with particulate Mn3O4 have shown that preweanling rats have substantially higher tissue Mn concentrations than similarly treated adults, indicating possible differences in uptake or elimination or both. This study was conducted to evaluate changes in gastrointestinal movement and retention of particulate Mn3O4 in the preweanling and weaned rat. 85Sr-labeled microspheres were used to evaluate gastrointestinal transit rate (TR), while particulate Mn3O4 was used to evaluate particulate retention at selected ages. The results show that stomach retention time in the preweanling is at least twice that of the postweanling (90 min versus 42 min). In general, intestinal TR was not different in any of the ages evaluated, while transit time increased as intestinal length increased. Analysis of the Mn data demonstrated that the preweanling rat had a two-component retention curve with half-times of between 2 and 6 h for the short component and of between 24 and 26 h for the long component. In the postweanling rat, only one component was identified, with a half-time of between 2 and 5 h.

Age-related dose response of selected reproductive parameters to acute cadmium chloride exposure in the male Long-Evans rat.

Groups of male Long-Evans rats 30, 50, or 70 d old were injected subcutaneously (sc) with a single dose of 0, 5.5, 11.5, or 24.6 mumol Cd/kg as cadmium chloride. All animals were killed 60 d after treatment. At 2 h prior to sacrifice, the rats were injected sc with 100 IU human chorionic gonadotrophin (hCG) to maximally stimulate serum testosterone concentrations. After sacrifice the testes, epididymides and seminal vesicles were removed and weighed. Cardiac blood was taken, and serum concentrations of testosterone (sT) and follicle-stimulating hormone (sFSH) were determined. Sperm concentration in luminal fluid collected from the vas deferens was determined. Significant (p less than 0.01) dose-dependent effects for all measured reproductive parameters were noted in the 70-d-old animals, while no effects were seen in the 30- or 50-d-old rats in either seminal vesicles weight or hCG-stimulated sT concentration. In the absence of significant (p greater than 0.05) changes in body weight gain, effects were seen in testes and epididymides weight, sperm concentration, and sFSH in the 70-d-old rats at Cd doses that were lower than those necessary to bring about similar changes in the 30- or 50-d-old animals. The sensitive indicators of Cd exposure in all age groups were testicular weight greater than epididymal weight greater than vas deferens sperm concentration greater than sFSH concentration. Seminal vesicle weight and sT concentration were found to be the least sensitive. Regression analyses indicated a significant interaction of age with dose; the 70-d-old rats required 30-61% less Cd/kg to cause a 50% change in a measured parameter than did the 30-d-old animals, while the 50-d-old rats required 15-47% less.

Possible antiestrogenic activity of lindane in female rats.

During chronic peroral (PO) treatment of weanling, female Fischer 344 rats with daily injections (0.069 mmol/kg) of either 1,1'-(2,2,2-trichloroethylidene) bis [4-chlorobenzene] (p,p'-DDT), 2,4-dichlorophenoxy acetic acid (2,4-D), or gamma-hexachlorocyclohexane (lindane), the lindane treatment induced a significant 20% increase in body weight after 110 days. Further investigation with 0, 5, 10, 20, and 40 mg/kg lindane confirmed a significant increase in average body weight gain at the two highest doses after ten weeks of treatment. Significantly greater food consumption was observed, and the Lee index indicated that lindane treatment induced obesity. In addition to obesity, lindane caused a delay in vaginal opening, disrupted estrous cycling, reduced pituitary and uterine weight, and elevated food consumption during proestrus (when appetite is normally suppressed by estradiol). These responses suggest that, by inducing alterations in the reproductive function of the female rat and by interfering with hormonal regulation of energy balance, lindane may be antiestrogenic rather than estrogenic as previously proposed.

Reproductive effects of low acute doses of cadmium chloride in adult male rats.

Adult male Sprague-Dawley rats were injected sc with cadmium (Cd, as cadmium chloride) in doses ranging from 1.6 to 152 mumol Cd/kg body weight (body wt). Fourteen days after dosing, animals were evaluated for reproductive damage. Evaluations for each animal included testes, seminal vesicles, and epididymides weights, vas deferens sperm concentration, and human chorionic gonadotropin (hCG)-stimulated serum testosterone concentration. Since 10 to 60% mortality occurred in the two highest dose groups (74 and 152 mumol/kg), no additional evaluations were conducted in these groups. The weights of the testes, seminal vesicles, and epididymides were reduced at least 40 to 50% in groups receiving 16 or 33 mumol Cd/kg while vas deferens sperm concentrations and hCG-stimulated serum testosterone concentrations were essentially zero. Significant depressions in the sperm concentrations and in the hCG-stimulated serum testosterone concentrations were found in animals receiving the two lowest doses (1.6 and 7.4 mumol Cd/kg) although no changes in tissue weights were observed in these animals. Curve-linear regression analyses for the dose responsiveness of these parameters demonstrated that serum testosterone concentration initially decreased at a rate of 19%/mumol Cd/kg, respectively, and was the most sensitive to Cd exposure. The initial rates of decrease for sperm concentrations and for seminal vesicles, testes, and epididymides weight were 6.45, 5.30, 4.19, and 2.45%/mumol Cd/kg, respectively, and were less responsive to Cd exposure than serum testosterone levels.

Effect of benomyl on the reproductive development of male rats.

Benomyl, a systemic fungicide, was administered to male Sprague-Dawley rats during the prepuberal, pubertal, or postpubertal stage of reproductive development. Animals received 5 or 10 daily treatments of 0, 125, 200, 250, 500, or 1000 mg benomyl/kg . d by gavage. Observations were made at selected intervals after exposure and included hematological parameters, body weight, tissue weights, total epididymal sperm counts, vas deferens sperm concentration, serum follicle-stimulating hormone ( sFSH ) levels, and testicular histology. Data presented here suggest that there is an age-related difference in sensitivity to benomyl. Animals that received benomyl treatments during prepuberty showed no significant treatment effects in tissue weights, total epididymal sperm counts, vas deferens sperm concentration, or sFSH . Animals that received at least 250 mg/kg . d during puberty or postpuberty showed one or more of the following effects: decreased testicular or epididymal weights, decreased epididymal sperm count, decreased vas deferens sperm concentrations, and/or testicular lesions. Histological examination of testicular tissue indicated a higher incidence of diffuse hypospermatocytogenesis in pubertal (20% of the treated animals) and postpubertal (40% of the treated animals) animals that were exposed to benomyl. These values were compared with those of the treated prepubertal animals, which had a 10% incidence of diffuse hypospermatocytogenesis , and with all of the control animals, which had no occurrences of this testicular lesion.

Effects of developmental hypothyroidism on auditory and motor function in the rat.

Deafness is a common result of severe hypothyroidism during development in humans and laboratory animals; however, little is known regarding the sensitivity of the auditory system to more moderate changes in thyroid hormone homeostasis. The current investigation compared the relative sensitivity of auditory function, motor function, and growth to the effects of moderate to severe perinatal hypothyroidism in the rat. Rats received propylthiouracil (PTU) in drinking water at concentrations of 0, 1, 5, and 25 ppm from Gestation Day 18 until postnatal day (PND) 21, and the effects on their offspring were evaluated. At 1 ppm, PTU did not affect any of the measured endpoints. Serum thyroxin concentrations were sharply reduced in the 5 and 25 ppm PTU groups at all ages sampled (PND 1, 7, 14, and 21). Marked reductions in serum triiodothyronine (T3) concentrations were also detected for all ages > or = 7 at 25 ppm PTU, whereas no effects of 5 ppm PTU on serum T3 were apparent until PND 21. Compared to the controls, pups exposed to the highest dose of PTU demonstrated a delay in eye opening, reduced body weights, decreased and/or delayed preweaning motor activity, and persistent, postweaning hyperactivity. Only slight and transient effects on eye opening and ontogeny of motor activity were seen at the intermediate dose of PTU (5 ppm). Reflex modification audiometry revealed that, compared to controls, adult offspring from the 5 and 25 ppm treatment groups showed dose-dependent auditory threshold deficits (35 to > 50 dB) at all frequencies tested (1, 4, 16, 32, and 40 kHz). Such dose-dependent effects indicate that the developing auditory system may be sensitive to mild hypothyroidism, suggesting the possible need for routine audiometric screening for infants and children at risk for iodine deficiency, myxedema, and/or exposure to thyrotoxic environmental agents.

Developmental exposure to polychlorinated biphenyls (Aroclor 1254) reduces circulating thyroid hormone concentrations and causes hearing deficits in rats.

Developmental hypothyroidism causes growth deficits, motor dysfunction, and hearing disorders in humans and animals. Therefore, environmental toxicants, such as polychlorinated biphenyls (PCBs), may secondarily affect these endpoints via thyrotoxicity. In this study, Long-Evans rats were given Aroclor 1254 (po), at 0, 1, 4, or 8 mg/kg from Gestation Day 6 through Postnatal Day (PND) 21. We evaluated the offspring at various age intervals for circulating thyroid hormone concentrations [thyroid-stimulating hormone, and free and total triiodothyronine (T3) and thyroxin (T4)], body weight, eye opening, survival, motor activity development, auditory startle response, and auditory thresholds. Circulating T4 concentrations were sharply reduced in a dose-dependent fashion in PCB-exposed groups at PND 1, 7, 14, 21, and 30 but recovered to control levels by PND 45. Moderate reductions in T3 concentrations were apparent in the 4 and 8 mg/kg groups on PND 21 and 30. Deficits in body weight gain and early eye opening were apparent in the treated pups; by weaning, pup mortality was 20% in the 4 mg/kg group and 50% at the highest dose. Motor activity was also transiently reduced in 15 day old offspring from the 8 mg/kg group. At this dose, animals showed reduced auditory startle amplitudes at PND 24, but not when tested as adults. Importantly, Aroclor 1254 caused permanent auditory deficits (20-30 dB threshold shift) at the lowest frequency tested (1 kHz) in both the 4 and 8 mg/kg groups, whereas auditory thresholds were not significantly affected at higher frequencies (4, 16, 32, or 40 kHz). These data indicate that while some effects of Aroclor 1254 exposure are dissimilar to drug-induced hypothyroidism (e.g., age of eye opening), effects on hormone levels and body weight are comparable. Detection of auditory deficits in PCB-treated animals is a novel finding and may reflect the effects of thyroid hormone disruption on the development of the cochlea.

Effects of chronic manganese (Mn3O4) exposure on selected reproductive parameters in rats.

Long-Evans rats were chronically exposed to dietary Mn3O4 beginning on d 1 of gestation and continuing through 224 d of age. Dietary concentrations of Mn, as Mn3O4, were 350, 1050, and 3500 ppm and were applied in either a normal Fe 240 ppm) or a low-Fe (20 ppm) basal diet. General toxic effects were apparent in young animals at a dietary dose of 3500 ppm Mn and were enhanced by concomitant Fe deficiency. Fertility was reduced in the group exposed to 3500 ppm Mn with a diet containing sufficient Fe. Male reproductive development was delayed by Mn treatment, as measured by testes weight, sperm count, and serum follicle-stimulating hormone and testosterone concentrations.

Chronic manganese oxide ingestion in rats: hematological effects.

Hematological values were studied in Long Evans rats after chronic exposure to manganese oxide (Mn3O4). Data were obtained at selected ages from the P0 through the F2 generation. Effects of exposure to Mn3O4 during Fe deficiency were determined by placing half of the animals on a low-Fe diet (20 mg/kg) while the other half were maintained on a normal-Fe diet (240 mg/kg). Animals treated with Mn3O4 and maintained on a normal-Fe diet showed little variation from controls through 100 d of age. However, animals (24-100 d of age) maintained on a low-Fe diet and receiving Mn treatment during the prenatal and postnatal periods developed microcytic anemia. Irrespective of the dietary Fe level, serum creatinine levels decreased in the groups receiving 400 and 1100 ppm Mn while serum Ca and P levels increased in the group receiving 1100 ppm Mn at 100 d of age. Serum values for lactate dehydrogenase, alkaline phosphatase (100 d of age), and serum glutamic-oxaloacetic transaminase (224 d of age) were elevated for all animals on low-Fe diets. Globulin, albumin (100 d of age), and glucose (224 d of age) levels were depressed in all low-Fe groups.

Chronic manganese oxide administration to preweanling rats: manganese accumulation and distribution.

Mn accumulation was evaluated in selected tissues of preweanling rats dosed daily with particulate Mn3O4. Significant findings include a high rate of Mn accumulation in the preweanling rat; a Mn dose-related acceleration of postpartum liver iron depletion; a Mn dose-related depression in red blood cells, hematocrit, hemoglobin, body weight, and survival by 21 d postpartum; and a Mn distribution in tissues with liver greater than brain greater than or equal to kidney greater than testes at 18-21 d of age.

Evaluation of reproductive parameters in adult male Wistar rats after subchronic exposure (gavage) to benomyl.

Proven-breeder 102-d-old male Wistar rats were gavaged daily with 0, 1, 5, 15, or 45 mg/kg.d benomyl. The animals were bred to untreated females after 62 d and killed after 76-79 d for evaluation of selected male reproductive end points. Minimal to moderate changes were observed in rats dosed with 45 mg/kg.d; these included decreased testis and epididymis weight, reduced cauda sperm reserves, decreased sperm production, increased numbers of decapitated spermatozoa, and increased numbers of seminiferous tubules containing multinucleated giant cells. Reproductive performance, seminal vesicle and prostate weight, sperm motility, serum luteinizing hormone, follicle-stimulating hormone, prolactin, and androgen binding protein were not affected by any of the dosages tested. Based on these end points, the no-effect level was 15 mg/kg.d.

Effects of low subchronic doses of methoxychlor on the rat hypothalamic-pituitary reproductive axis.

The pesticide methoxychlor (MXC) is known to possess a weak estrogenic action and has been found to have a number of toxic effects on the rodent reproductive system, primarily at the gonadal level. The purpose of this study was to explore the influence of MXC on the pituitary and hypothalamic components of the male reproductive system at dose levels that were without detectable testicular effects. At 21 days, male Long-Evans rats were gavaged daily with 25 or 50 mg/kg MXC in corn oil. Controls received vehicle only. After 8 weeks of dosing, no significant changes were seen in serum LH, FSH, or prolactin, nor in the pituitary concentrations of LH or FSH. Pituitary prolactin was elevated for both doses, and pituitary fragments perifused in vitro released more prolactin than did controls. The concentration of gonadotropin-releasing hormone (GnRH) was higher in the mediobasal hypothalamus, but only for the 50-mg/kg group. At this dose, there was a corresponding increase in the KCl-stimulated release of GnRH. The data suggest that previously reported reproductive effects of MXC may be mediated, at least in part, through an elevation in prolactin concentration and release, which in turn is able to influence hypothalamic levels of GnRH. This prolactinemic effect may well represent an early component of the adverse action of MXC on the reproductive system.

Assessment of the male reproductive system in the preweanling rat following Mn3O4 exposure.

Long-Evans rat pups were dosed orally from birth to 21 d with particulate Mn3O4 to obtain a daily dose of 0, 71, or 214 micrograms Mn/body weight . d. Assessments of the hypothalamic, pituitary, or testicular functions were determined by measuring the endogenous or stimulated serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and/or testosterone (T) at 21 or 28 d of age. Body, testes, and seminal vesicles weight and tissue concentrations of Mn were also evaluated. Only slight Mn treatment effects were seen in body and testes weights. No effects were seen either on unstimulated or stimulated FSH or LH serum concentrations. Although no Mn treatment effects were seen on endogenous or 2 h human chorionic gonadotropin (hCG) stimulate serum T concentrations, there was a reduction in the serum T following 7 d of hCG stimulation. The hypothalamic Mn concentrations in animals with these reproductive effects were three times those where alterations in the dopaminergic pathway have been reported. However, no indication of hypothalamic or pituitary malfunction was found. These results suggest that the site of Mn damage that causes depression of sustained serum T concentration is in the testicular Leydig cell.