Influence of chronic lead exposure on hormone levels in developing rats

Protective role of ascorbic acid on lead-induced damage to the thyroid gland in the rat

Lead exposure is known to affect the pituitary-thyroid axis. Likewise, ascorbic acid (AA) has a protective action against lead poisoning. We examine the protective role of AA in lead-induced damage to the thyroid gland. The Wistar rats were divided into three groups: control that received 0.2% AA in drinking water throughout the experiment (15 days), intoxicated with lead acetate (20 mg/kg) intraperitoneally every 48 h for 15 days, and the experimental group treated with lead acetate and 0.2% AA in drinking water throughout the experiment. Plasma thyroid-stimulating hormone, triiodothyronine, thyroxine, and lead were determined. The thyroid gland was weighed, then epithelial cell height and nuclear volume were measured on histological slides. The results show that AA reduced the thyroid atrophy caused by lead acetate, as well as the loss of weight of the gland. In addition, it prevented the decrease of the hormone triiodothyronine, although the thyroxine hormone remained lower than the control values ​​and the thyroid-stimulating hormone remains high. Our results indicated that AA could play a protective role in lead poisoning in the thyroid gland.

Developmental Lead Exposure and Prenatal Stress Result in Sex-Specific Reprograming of Adult Stress Physiology and Epigenetic Profiles in Brain

Developmental exposure to lead (Pb) and prenatal stress (PS) both impair cognition, which could derive from their joint targeting of the hypothalamic-pituitary-adrenal axis and the brain mesocorticolimbic (MESO) system, including frontal cortex (FC) and hippocampus (HIPP). Glucocorticoids modulate both FC and HIPP function and associated mediation of cognitive and other behavioral functions. This study sought to determine whether developmental Pb ± PS exposures altered glucocorticoid-related epigenetic profiles in brain MESO regions in offspring of female mice exposed to 0 or 100 ppm Pb acetate drinking water from 2 mos prior to breeding until weaning, with half further exposed to prenatal restraint stress from gestational day 11-18. Overall, changes in females occured in response to Pb exposure. In males, however, Pb-induced neurotoxicity was modulated by PS. Changes in serum corticosterone levels were seen in males, while glucocorticoid receptor changes were seen in both sexes. In contrast, both Pb and PS broadly impacted brain DNA methyltransferases and binding proteins, particularly DNMT1, DNMT3a and methyl-CpG-binding protein 2, with patterns that differed by sex and brain regions. Specifically, in males, effects on FC epigenetic modifiers were primarily influenced by Pb, whereas extensive changes in HIPP were produced by PS. In females, Pb exposure and not PS primarily altered epigenetic modifiers in both FC and HIPP. Collectively, these findings indicate that epigenetic mechanisms may underlie associated neurotoxicity of Pb and of PS, particularly associated cognitive deficits. However, mechanisms by which this may occur will be different in males versus females.

Withania somnifera ameliorates lead-induced augmentation of adrenergic response in rat portal vein

OBJECTIVES

Present study was undertaken to elucidate the ameliorating potential of Withania somnifera root extract (WRE) against lead-induced augmentation of adrenergic response in rat portal vein.

MATERIALS AND METHODS

In-vitro studies were conducted on effect of lead alone and lead+WRE on rat-isolated portal vein while in-vivo studies were done in three groups of 12 rats each; Group-II and III received 0.5% lead acetate and 1.0% WRE + 0.5% lead acetate, respectively, in drinking water for 12 weeks whereas group-I served as control. Adrenaline and noradrenaline levels in brain and blood were determined by HPLC assay while vascular reactivity of portal vein to lead and WRE was determined by measuring the isometric tension.

RESULTS

Following in-vitro exposure, lead did not alter the contractile effect of phenylephrine. In-vivo studies revealed that contractile effect of lead on portal vein was significantly potentiated and it was antagonized by prazosin (10(-7) M) and WRE (1%). WRE treatment significantly reduced elevated blood noradrenaline (37.80%) and restored noradrenaline level in brain (39.39%) in lead-exposed animals. These values were almost comparable to the control group. But it failed to significantly affect the blood and brain adrenaline levels.

CONCLUSIONS

Results suggest that following pre-exposure of rats to WRE, lead-induced augmentation of alpha 1-adrenoceptors mediated response was reversed possibly by regulating catecholamine release from nerve endings. Thus, WRE may be useful in therapeutic management of lead-induced hypertension.

Effect of long-term dietary lead exposure on some maturation and reproductive parameters of a female Prussian carp (Carassius gibelio B.)

Lead is reported to be an endocrine disruptor. In the current study, we exposed female Prussian carp to artificial feed, supplemented with five doses of dietary Pb (0, 1 (control), 8, 13, 24, and 49 mg/kg) over either a 24-month period or a 12-month period, followed by further 12 months where the fish were fed the control diet. Periodically, oocyte maturation, gonadosomatic index (GSI), ability to secret luteinizing hormone (LH) as well as gonad Pb concentrations were measured. It was found that the reproductive system of the female Prussian carp is not indifferent to chronic exposure to lead. The negative effect was manifested by a decrease in the GSI after 12 months despite the fact that a higher proportion of oocytes at more advanced maturity stages were concurrently observed. After 12 months of exposure, the effect on LH secretion varied according to the dose. In the group exposed to the lowest dose (8 mg/kg), LH decreased spontaneously, and in the groups exposed to the highest two doses (24 and 48 mg/kg), a significantly higher LHRH-A-stimulated LH secretion was observed. After 24 months of lead exposure, the effects on oocyte maturation and size and on GSI values were not pronounced. Analysis of the effect of lead exposure on LH secretion showed that the relationships were similar to those observed after 12 months but nonsignificant. During chronic a 24-month period exposure to Pb, Prussian carp female appears to acclimate to Pb doses used in the experiment. After 12 months of exposure and 12 months of depuration, the levels of spontaneous and stimulated LH secretion observed in all the groups were similar to the control, which is evidence that depuration eliminates the previously observed effects of exposure to lead. Lead is easily accumulated in the ovary, reaching a fivefold higher level (0.8 mg/kg tissue) compared to the control(0.15 mg/kg tissue), but after discontinuation of exposure, this organ is quickly depurated. The results indicate that environmental Pb can be a potent endocrine disruptor affecting ovarian steroidogenesis, gametogenesis, and ovulation, which may lead to adverse impacts on fish reproduction and population density and that female Prussian carp become resistant to the negative effects of lead with advancing age, and their organs cope by reaching a state of homeostasis.

Effect of estradiol on heme biosynthetic pathway in lead-poisoned rabbits

OBJECTIVES

To clarify the effect of the female hormone estradiol (Est) on heme biosynthesis in lead-poisoned rabbits, parameters indicating lead exposure, such as free erythrocyte protoporphyrin (FEP) level and δ-aminolevulinic acid dehydratase (ALA-D) activity, were determined.

METHODS

Twenty-six male Japanese white rabbits (body weight (BW), 3kg) were divided into four groups: I (control), II (Est), III (Pb), IV (Est+Pb). About 3 weeks after castration, Est (3 mg/kg of BW) was injected intramuscularly, and 2 weeks thereafter, lead (1.2 mg/kg of BW) was injected intravenously. After the initial injection of each of these substances, the same dose of each of these substances was injected once a week until the 9th week.

RESULTS

In groups III and IV, FEP level increased and ALA-D activity in the erythrocytes, bone marrow and liver decreased with an increase in lead concentration in blood. FEP level decreased significantly (p<0.01) in the 8th and 10th weeks after Est injection in group IV compared to with that in group III and was not elevated in group II compared with that in group I. ALA-D activity in the erythrocytes, bone marrow and liver increased significantly in group II compared with that in group I, whereas Ht and Hb levels decreased in group II compared with those in group I, and decreased in group IV compared with those in group III. The level of iron in plasma (Fe-P) was within the normal range during experiment.

CONCLUSIONS

In this study, Est did not increase FEP level. From the above results regarding FEP level and ALA-D activity, Est may prevent an increase in FEP level caused by lead. Ht and Hb levels, which are the parameters of anemia, decreased mainly as a result of Est exposure rather than lead exposure.

A transdisciplinary perspective of chronic stress in relation to psychopathology throughout life span development

The allostatic load (AL) model represents an interdisciplinary approach to comprehensively conceptualize and quantify chronic stress in relation to pathologies throughout the life cycle. This article first reviews the AL model, followed by interactions among early adversity, genetics, environmental toxins, as well as distinctions among sex, gender, and sex hormones as integral antecedents of AL. We next explore perspectives on severe mental illness, dementia, and caregiving as unique human models of AL that merit future investigations in the field of developmental psychopathology. A complimenting transdisciplinary perspective is applied throughout, whereby we argue that the AL model goes beyond traditional stress–disease theories toward the advancement of person-centered research and practice that promote not only physical health but also mental health.

The effect of lead intoxication on endocrine functions

Studies on the effects of lead on the endocrine system are mainly based on occupationally lead-exposed workers and experimental animal models. Although evidence is conflicting, it has been reported that accumulation of lead affects the majority of the endocrine glands. In particular, it appears to have an effect on the hypothalamic-pituitary axis causing blunted TSH, GH, and FSH/LH responses to TRH, GHRH, and GnRH stimulation, respectively. Suppressed GH release has been reported, probably caused by reduced synthesis of GHRH, inhibition of GHRH release or reduced somatotrope responsiveness. Higher levels of PRL in lead intoxication have been reported. In short-term lead-exposed individuals, high LH and FSH levels are usually associated to normal testosterone concentrations, whereas in long-term exposed individuals' low testosterone levels do not induce high LH and FSH concentrations. These findings suggest that lead initially causes some subclinical testicular damage, followed by hypothalamic or pituitary disturbance when longer periods of exposure take place. Similarly, lead accumulates in granulosa cells of the ovary, causing delays in growth and pubertal development and reduced fertility in females. In the parenchyma of adrenals histological and cytological changes are demonstrated, causing changes in plasma basal and stress-mediated corticosterone concentrations and reduced cytosolic and nuclear glucocorticoid receptor binding. Thyroid hormone kinetics are also affected. Central defect of the thyroid axis or an alteration in T4 metabolism or binding to proteins may be involved in derangements in thyroid hormone action. Lead toxicity involves alterations on calcitropic hormones' homeostasis, which increase the risk of skeletal disorders.

Lifetime consequences of combined maternal lead and stress

Elevated lead (Pb) exposure and high stress both target low socio-economic status populations. Both also act on the hypothalamic-pituitary-adrenal (HPA) axis. Pb disrupts cognition through effects on the mesocorticolimbic dopamine pathway. Stress hormones act on this same pathway via the HPA axis. The fact that Pb and stress are likely interactive risk factors served as the rationale for a series of studies in our laboratory. These demonstrate that stress can modify Pb effects, that Pb can modify stress responsivity, and, notably, that Pb + stress effects can occur in the absence of an effect of either alone in rats. Furthermore, maternal only Pb exposure can permanently alter basal corticosterone levels, stress responsivity (i.e. permanent modification of HPA axis function) and brain catecholamines in offspring of both genders. Interactive effects of Pb + stress are not limited to early development: even Pb exposures initiated post-weaning alter basal corticosterone and stress responsivity. Outcomes differ in relation to gender, brain region, stressor and time of measurement, making Pb + stress interactions complex. Altered HPA axis function may serve as a mechanism for the behavioural and catecholaminergic neurotoxicity associated with Pb, as well as for the increased incidence of disease and dysfunctions associated with low socio-economic status. The permanent consequences of maternal only Pb exposure suggest that Pb screening programmes should include pregnant women at risk for elevated Pb exposure, and that stress should be considered as an additional risk factor. Pb + stress effects observed in the absence of either risk factor alone raise questions about the capacity of current hazard identification approaches to adequately identify human health risks posed by neurotoxicants.

Low-level prenatal and postnatal blood lead exposure and adrenocortical responses to acute stress in children

BACKGROUND

A few recent studies have demonstrated heightened hypothalamic-pituitary-adrenal (HPA) axis reactivity to acute stress in animals exposed to heavy metal contaminants, particularly lead. However, Pb-induced dysregulation of the HPA axis has not yet been studied in humans.

OBJECTIVE

In this study, we examined children's cortisol response to acute stress (the glucocorticoid product of HPA activation) in relation to low-level prenatal and postnatal Pb exposure.

METHODS

Children's prenatal blood Pb levels were determined from cord blood specimens, and postnatal lead levels were abstracted from pediatrician and state records. Children's adrenocortical responses to an acute stressor were measured using assays of salivary cortisol before and after administration of a standard cold pressor task.

RESULTS

Pb exposure was not associated with initial salivary cortisol levels. After an acute stressor, however, increasing prenatal and postnatal blood Pb levels were independently associated with significantly heightened salivary cortisol responses.

CONCLUSIONS

Our results suggest that relatively low prenatal and postnatal blood lead levels--notably those below the 10 microg/dL blood lead level identified by the Centers for Disease Control and Prevention for public health purposes--can alter children's adrenocortical responses to acute stress. The behavioral and health consequences of this Pb-induced HPA dysregulation in children have yet to be determined.

Effects of zinc coadministration on lead toxicities in rats

In order to investigate the effects of Zn on Pb toxicities. Proportion of abnormal sperm, percentage of micronucleated polychromatic erythrocyte (MPCE), serum thyroid hormones (T(3), T(4)) and cortisol were measured. Rats received intraperitoneal injection of 25 mg/kg Pb acetate, 4 mg/kg Zn acetate, both Pb acetate and Zn acetate, or normal saline as controls, once every two days, 7 times in total. No significant differences in whole blood Pb were detected between groups received Pb alone or both Pb and Zn. On the contrary, the concentration of whole blood Zn in the group given Zn alone was significantly higher than that in the group that received both Pb and Zn. In the groups given Pb alone or both Pb and Zn, proportion of abnormal sperm, frequency of MPCE and serum cortisol were significantly higher than those in controls, whereas serum T(3) and T(4) were significantly lower than in controls. In the group given both Pb and Zn, T(4) was decreased most obviously among the four groups. While the proportion of abnormal sperm was less in the group given both Pb and Zn than in the group given Pb alone. These findings suggest that Zn coadministration might alleviate toxic effects of Pb on the male reproductive system, whereas it could enhance the toxicity on thyroid function. Zn did not affect the toxicities of Pb on cytogenetic systems as indicated by MPCE percentage, and on serum cortisol levels under the dose of the present study. Our results suggested the double-edged effects of Zn on Pb toxicities in different organs. Therefore, the effects of Zn on Pb toxicities should be evaluated systematically.

Stress as a potential modifier of the impact of lead levels on blood pressure: the normative aging study

BACKGROUND

Lead exposure and psychological stress have been independently associated with hypertension in various populations, and animal studies suggest that when they co-occur, their effects may be exacerbated.

OBJECTIVES

We examined whether psychological stress modifies the impact of cumulative lead exposure (measured as bone lead levels) on hypertension and blood pressure in Boston-area community-exposed men participating in the Normative Aging Study.

METHODS

We evaluated the modifying effect of stress on lead exposure on baseline hypertension status (513 participants) and on blood pressure in those without hypertension (237 participants), cross-sectionally. In baseline nonhypertensives, we examined the same risk factors in relation to prospective risk of developing hypertension.

RESULTS

Cross-sectional analysis revealed a positive interaction between stress and tibia lead on systolic blood pressure, after adjusting for age, body mass index, family history of high blood pressure, education, smoking, alcohol consumption, physical activity, and nutritional factors. In prospective multivariate analyses, high stress also modified the effect of tibia lead and patella lead on the risk of developing hypertension. Those reporting high stress had 2.66 [95% confidence interval (CI), 1.43-4.95] times the risk of developing hypertension per standard deviation increase in tibia lead and had 2.64 (95% CI, 1.42-4.92) times the risk per standard deviation increase in patella lead.

CONCLUSION

To our knowledge, these are the first analyses to look at interactive effects of stress and lead on hypertension in humans. These results suggest that the effect of lead on hypertension is most pronounced among highly stressed individuals, independent of demographic and behavioral risk factors.

Changes in plasma hormones profile and liver function in cows naturally exposed to lead and cadmium around different industrial areas

The present study was carried out to assess the endocrine status and liver function in adult cows reared in polluted environment around different industrial units in India. The effect on endocrine system was examined by determination of plasma level of thyroid hormones, thyroxin (T4) (n=269) and triidothyronin (T3) (n=269), stress hormone cortisol (n=266), and reproductive hormones such as estradiol (n=84) and progesterone (n=84) in cows (>3 years) reared around different polluted industrial and non-polluted areas. The respective blood lead and cadmium concentration was also determined in all the cows. The mean plasma levels of both T3 and T4 were significantly (P<0.05) higher around lead zinc smelter (2.43+/-0.26 and 41.1+/-2.9nmol/L) and closed lead cum operational zinc smelter (1.81+/-0.16 and 42.4+/-6.2nmol/L), where the mean blood lead level (0.86+/-0.06 and 0.51+/-0.09mug/ml) was also significantly higher than that of cows (0.07+/-0.01mug/ml) from unpolluted areas. Regression analysis of data from 269 cows revealed a significant (P<0.01) positive correlation between the blood lead and plasma T3 (r=0.287) and T4 (r=0.173). The correlation between thyroidal hormones and the blood cadmium concentration (r=-0.079 and -0.48; P>0.05) was not significant. Plasma cortisol level had also a non-significant (P>0.05) correlation (r=-0.092) with blood lead level.However, the mean cortisol level (4.02+/-1.96nmol/L) of cows in phosphate rock mining areas was significantly (P<0.05) higher than that of controls (1.98+/-0.70nmol/L). The mean plasma estradiol level was significantly (P<0.05) higher in cows around closed lead cum operational zinc smelter (47.1+/-19.5pg/ml) than that of the control animals (21.8+/-3.9pg/ml) and in rest of the areas, the difference did not reach the statistical significance (P>0.05). The serum biochemical analysis in 36 cows around lead-zinc smelter with the highest mean blood lead level (0.86+/-0.06mug/ml) amongst all the industrial/urban areas surveyed, and in 15 animals from non-polluted areas revealed a significant positive correlation between blood lead and serum ALT (alanine transaminase) (r=0.688, P<0.01) and AST (aspartate transaminase) (r=0.390, P<0.01) and a negative correlation with serum total lipids (r=-0.337, P<0.05), total protein (r=-0.449, P<0.01) and albumin(r=-0.662, P<0.01). It is concluded from the study that the natural exposure to lead in polluted environments disturbs the endocrine profile and the higher blood lead level alters serum biochemical parameters indicative of liver functions.

Adrenocortical response to stress and thyroid hormone status in free-living nestling white storks (Ciconia ciconia) exposed to heavy metal and arsenic contamination

BACKGROUND/OBJECTIVE

Endocrine parameters have proven useful in the detection of early or low-level responses to pollutants. Although most of the studies on endocrine modulation have been focused on processes involving gonadal steroids, contaminants may target other parts of the endocrine system as well. In this study we examined the adrenocortical stress response and thyroid hormone status in free-living nestling white storks (Ciconia ciconia) in relation to heavy metals (zinc, lead, copper, cadmium) and arsenic levels in blood.

METHODS

Fieldwork was conducted in an area polluted by the Aznalcóllar mine accident (southwestern Spain) and in a reference site. We used a standardized capture, handling, and restraint protocol to determine both baseline and maximum plasma corticosterone. Circulating levels of thyroxine (T4) and triiodothyronine (T3) were also measured.

RESULTS

No effects of metals or As were found on baseline corticosterone, but maximum levels of corticosterone were positively related to Pb in both locations. This relationship was stronger in single nestlings than in birds from multiple-chick broods, which suggests a greater impact of Pb on more stressed individuals. Metal pollution did not affect plasma T4 or T3 levels, although thyroid status differed with location.

CONCLUSIONS

Because a compromised hypothalamus-pituitary-adrenal (HPA) function can have far-reaching consequences in terms of altered behavioral and metabolic processes necessary for survival, our results suggest that birds exposed to sublethal Pb levels may be at risk through an altered adrenocortical stress response, and further support the idea that HPA axis-related end points might be useful indicators of metal exposure and potential toxicity in wild animals.

Lead exposure through gestation-only caused long-term learning/memory deficits in young adult offspring

Numerous observations in clinical and preclinical studies indicate that the developing brain is particular sensitive to lead (Pb)'s pernicious effects. However, the effect of gestation-only Pb exposure on cognitive functions at maturation has not been studied. We investigated the potential effects of three levels of Pb exposure (low, middle, and high Pb: 0.03%, 0.09%, and 0.27% of lead acetate-containing diets) at the gestational period on the spatial memory of young adult offspring by Morris water maze spatial learning and fixed location/visible platform tasks. Our results revealed that three levels of Pb exposure significantly impaired memory retrieval in male offspring, but only female offspring at low levels of Pb exposure showed impairment of memory retrieval. These impairments were not due to the gross disturbances in motor performance and in vision because these animals performed the fixed location/visible platform task as well as controls, indicating that the specific aspects of spatial learning/memory were impaired. These results suggest that exposure to Pb during the gestational period is sufficient to cause long-term learning/memory deficits in young adult offspring.

Time-dependent effects of lead on rat reproductive functions

The effects of exposure to lead on endocrine function and the reproductive parameters were studied in pubertal rats treated with 1.0 g l-1 lead acetate in drinking water for 20 days (subacute group) or 9 months (chronic group) in addition to i.v. injections of lead acetate (0.1 mg 100 g-1 body wt.) every 10 (subacute group) or 15 days (chronic group). Although basal levels of testosterone were higher both in plasma and in testes of acutely intoxicated animals, the circulating levels of luteinizing hormone (LH) were not affected in either group, nor was the LH-releasing hormone content of the median eminence. The density of [125I]LH/human chorionic gonadotrophin (hCG) binding sites in testicular homogenates was reduced by saturnism in both groups, concomitant with a significantly increased apparent affinity constant of the hormone-receptor complex. These data can be viewed as the result of a mixture of specific lead toxicity (e.g. at the enzyme level) with other more general actions (e.g. at the level of the hypothalamus-pituitary-testicular axis).