Lead (Pb) alters the norepinephrine-induced secretion of luteinizing hormone releasing hormone from the median eminence of adult male rats in vitro

Lead exposure and its relationship with fecal cortisol levels in black howler monkeys (Alouatta pigra)

Efficiently detecting early environmental threats to wildlife is vital for conservation. Beyond obvious dangers like habitat loss or deforestation, our study focuses on one of the most hazardous toxic metals for wildlife: lead (Pb). Pb is a widespread, cumulative, and insidious environmental pollutant that can trigger a wide range of physiological, biochemical, and behavioral disorders. In fact, Pb can cause permanent dysfunction of the major stress system, the hypothalamic pituitary adrenal (HPA) axis. We analyzed Pb and cortisol concentrations in fecal samples from Alouatta pigra in southern Mexico. Fecal samples were collected across six sites categorized as free-ranging (n = 65; conserved and disturbed) and from captive animals (n = 58). Additionally, we collected soil samples (n = 35). We found that Pb was present in 28% of fecal samples and 83% of soil samples. There was a positive relation between fecal and soil Pb levels, and fecal Pb concentration was negatively associated with cortisol levels. However, the claim of Pb being a direct interference with HPA axis requires further investigation. Given our findings, assessing wildlife exposure can be a valuable tool for understanding potential Pb exposure levels in the environment and its possible implications for human health. It can also serve as an early warning system of these consequences.

Cross-species coherence in effects and modes of action in support of causality determinations in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead

The peer-reviewed literature on the health and ecological effects of lead (Pb) indicates common effects and underlying modes of action across multiple organisms for several endpoints. Based on such observations, the United States (U.S.) Environmental Protection Agency (EPA) applied a cross-species approach in the 2013 Integrated Science Assessment (ISA) for Lead for evaluating the causality of relationships between Pb exposure and specific endpoints that are shared by humans, laboratory animals, and ecological receptors (i.e., hematological effects, reproductive and developmental effects, and nervous system effects). Other effects of Pb (i.e., cardiovascular, renal, and inflammatory responses) are less commonly assessed in aquatic and terrestrial wildlife limiting the application of cross-species comparisons. Determinations of causality in ISAs are guided by a framework for classifying the weight of evidence across scientific disciplines and across related effects by considering aspects such as biological plausibility and coherence. As illustrated for effects of Pb where evidence across species exists, the integration of coherent effects and common underlying modes of action can serve as a means to substantiate conclusions regarding the causal nature of the health and ecological effects of environmental toxicants.

The relationships between blood lead levels and serum follicle stimulating hormone and luteinizing hormone in the National Health and Nutrition Examination Survey 1999-2002

The relationships between blood lead levels and serum follicle stimulating hormone and luteinizing hormone were assessed in a nationally representative sample of women, 35-60 years old, from the National Health and Nutrition Examination Survey 1999-2002. The blood lead levels of the women ranged from 0.2 to 17.0 μg/dL. The estimated geometric mean was 1.4 μg/dL, and the estimated arithmetic mean was 1.6 μg/dL. As the blood lead level increased, the concentration of serum follicle stimulating hormone increased in post-menopausal women, women who had both ovaries removed, and pre-menopausal women. The concentration of luteinizing hormone increased as blood lead level increased in post-menopausal women and women who had both ovaries removed. The lowest concentrations of blood lead at which a relationship was detected were 0.9 μg/dL for follicle stimulating hormone and 3.2 μg/dL for luteinizing hormone. Lead may act directly or indirectly at ovarian and non-ovarian sites to increase the concentrations of follicle stimulating hormone and luteinizing hormone.

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.

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.

Lead-induced cell signaling cascades in GT1-7 cells

The effects of lead on the signal transduction pathways that may be involved in the release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus have not been well defined. Using the GT1-7 cell line, an in vitro model for GnRH-secreting neurons, we examined signal transduction pathways directly affected by lead. We found that lead-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2), as well as p90RSK and cAMP response element-binding protein (CREB), but did not induce IkappaB degradation. MEK1/2 inhibitor (PD98059) suppressed lead-induced ERK and p90RSK activation. Neither PKC inhibitors (Go6983, Go6976) nor CaMKII inhibitor (KN-62) had a pronounced effect on lead-induced ERK1 and ERK2 phosphorylation. However, MEK1/2 inhibitor, CaMKII inhibitor, and PKC inhibitor significantly suppressed lead-induced CREB phosphorylation. These results indicate that lead-activated PKC, CaMKII and MEK/ERK/p90RSK pathways simultaneously, all of which contributed to CREB phosphorylation. Our results also indicate that lead-induced p90RSK and CREB activation does not alter expression of early response genes like c-fos. We conclude that lead activates PKC, CaMKII or MEK-ERK-p90RSK pathways in GT1-7 cells, leading to CREB phosphorylation and modulation of gene expression.

Effects of combined exposure to lead and cadmium on the hypothalamic-pituitary axis function in proestrous rats

The effects of lead and cadmium on the hypothalamic-pituitary axis were studied in proestrous rats. Adult female rats were treated intraperitonially with either lead acetate and cadmium acetate alone or in combination at a dose of 0.05 mg/kg daily for 15 days. Serotonin (5-HT) and norepinephrine (NE) levels decreased in individually and combined metal treated groups whereas dopamine (DA) levels were decreased only in the cadmium-exposed group. The pituitary levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were decreased significantly in cadmium and combined treatment groups. In contrast, lead exposure failed to cause any change in serum LH and FSH levels, whereas cadmium and combined treatments showed significant decrease in serum LH and FSH levels as compared with control. The accumulation of both metals increased in the hypothalamus and pituitary after treatment. These data suggest that the metal accumulation disrupts the regulatory mechanisms of the hypothalamic-pituitary axis where the effects produced by the combined treatment of metals are not additive.

Effects of lead (Pb) exposure during gestation and lactation on female pubertal development in the rat

Lead (Pb) can delay sexual maturation; however, the mechanism and critical time of insult are not clearly defined. Therefore, we assessed maternal Pb levels during low-level gestational and/or lactational exposure, as well as blood and tissue Pb in developing fetuses in relation to the subsequent detrimental effects of Pb on puberty-related hormones and the onset of female puberty. Adult Fisher 344 female rats were gavaged daily with either a 1-ml solution of PbAc containing 12 mg/ml Pb or an equal volume of sodium acetate (NaCl), for the controls, from 30 days prior to breeding until their pups were weaned at 21 days. By cross-fostering at the time of birth, the pups were either exposed to PbAc or NaAc during gestation only, lactation only, or during both gestation and lactation. Pb delayed the timing of puberty and this delay was associated with suppressed serum levels of insulin-like growth factor-1 (IGF-1), luteinizing hormone (LH), and estradiol (E(2)). Liver IGF-1 mRNA was not affected, suggesting that Pb altered translation and/or secretion of IGF-1. We reported previously that peripherally derived IGF-1 acts at the hypothalamic level to facilitate LH release at puberty; hence, we suggest that the action of Pb in decreasing circulating IGF-1 contributes to the delayed puberty. The detrimental effects occurred regardless of the developmental time of exposure, although gestational exposure appeared more sensitive to the effects of Pb. Also, the effects noted were with blood Pb levels less than previously reported and these levels are relevant to human health concerns.

Role of early GnRH administration in sexual behavior disorders of rat pups perinatally exposed to lead

The effects of maternal exposure to lead (Pb) during the perinatal (1% and 0.1% Pb) periods of sexual brain differentiation were studied in adult male offspring. Maternal Pb levels were measured after treatment. Behavioral (open field and sexual behavior), physical (sexual maturation, body and organ weights), and biochemical (testosterone levels and hypothalamic monoamine and respective metabolite levels) data were assessed in perinatally exposed offspring. The effects of gonadrotopin-releasing hormone (GnRH) administration to pups at birth on puberty and sexual behavior were also investigated in offspring postnatally exposed to the metal. Results showed that perinatal administration of the two Pb concentrations did not modify maternal weight gain; 1% Pb exposure reduced offspring body weight during the 7 days of treatment while no changes were observed after 0.1% Pb exposure; neither Pb concentration altered offspring sexual maturation; the higher Pb concentration improved sexual behavior while the 0.1% concentration reduced it; exposure to 0.1% Pb caused decrease in testis weight, an increase in seminal vesicle weight and no changes in plasma testosterone levels; hypothalamic VMA levels were increased compared to the control group; GnRH administration reversed the effects of 0.1% Pb administration on male sexual behavior. These results show that perinatal exposure to Pb had a dose-dependent effect on the sexual behavior of rats and that a decrease in GnRH source in the offspring was probably involved in the reduction of their sexual performance.