Toxic effects of methoxychlor on the episodic prolactin secretory pattern: possible mediated effects of nitric oxide production

Endocrine-disrupting and cytotoxic potential of anticholinesterase insecticide, diazinon in reproductive toxicity of male mice

We evaluated the effects of diazinon (2, 4.1 and 8.2mg/kg bw/day for 4 weeks) in gonadotropins, testosterone and estrogen levels, whether the regulatory interactions in the hypothalamic-pituitary-testicular axis are modified by acetylcholinesterase inhibition and histopathological changes in adult mice testes. Diazinon at doses higher than 2mg/kg bw/day resulted in decreased testis weight, inhibition in acetylcholinesterase activities, decrease in levels of luteinizing hormone and follicle stimulating hormone, following reduction in mating and fertility indices. Diazinon increased testosterone content in 4.1mg/kg group, but decreased testosterone concentration in 8.2mg/kg group. Diazinon increased estrogen, prolactine and decreased levels of acetylcholinesterase activities in 4.1mg/kg group but levels of luteinizing hormone and follicle stimulating hormone remained unmodified. It may be simply postulated a scenario that acetylcholine in the cholinergic neurons has a potential threshold to perform a crucial part in the complex circuitry of neuroendocrine regulatory mechanisms. On overaccumulation, other neurotransmitters can be appropriately recruited to modulate the mechanisms of circuitry.

Nitric oxide signaling as a common target of organohalogens and other neuroendocrine disruptors

Organohalogen compounds such as polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE) are global environmental pollutants and highly persistent, bioaccumulative chemicals that produce adverse effects in humans and wildlife. Because of the widespread use of these organohalogens in household items and consumer products, indoor contamination is a significant source of human exposure, especially for children. One significant concern with regard to health effects associated with exposure to organohalogens is endocrine disruption. Toxicological studies on organohalogen pollutants primarily focused on sex steroid and thyroid hormone actions, and findings have largely shaped the way one envisions their disruptive effects occurring. Organohalogens exert additional effects on other systems including other complex endocrine systems that may be disregulated at various levels of organization. Over the last 20 years evidence has mounted in favor of a critical role of nitric oxide (NO) in numerous functions ranging from neuroendocrine functions to learning and memory. With its participation in multiple systems and action at several levels of integration, NO signaling has a pervasive influence on nervous and endocrine functions. Like blockers of NO synthesis, PCBs and PBDEs produce multifaceted effects on physiological systems. Based on this unique set of converging information it is proposed that organohalogen actions occur, in part, by hijacking processes associated with this ubiquitous bioactive molecule. The current review examines the emerging evidence for NO involvement in selected organohalogen actions and includes recent progress from our laboratory that adds to our current understanding of the actions of organohalogens within hypothalamic neuroendocrine circuits. The thyroid, vasopressin, and reproductive systems as well as processes associated with long-term potentiation were selected as sample targets of organohalogens that rely on regulation by NO. Information is provided about other toxicants with demonstrated interference of NO signaling. Our focus on the convergence between NO system and organohalogen toxicity offers a novel approach to understanding endocrine and neuroendocrine disruption that is particularly problematic for developing organisms. This new working model is proposed as a way to encourage future study in elucidating common mechanisms of action that are selected with a better operational understanding of the systems affected.

Toxic effects of methoxychlor administered subcutaneously on the hypothalamic-pituitary-testicular axis in adult rats

This study was undertaken to evaluate the effects of methoxychlor MTX at the hypothalamic-pituitary-testicular axis in adult male rats. This global objective comprises three major aims: (1) to analyze the possible differential MTX effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence; (2) to evaluate effects induced by MTX exposure on gonadotropins and testosterone; 93 to elucidate whether the regulatory interactions in the hypothalamic-pituitary-testicular axis are modified by this pesticide. Animals were administered subcutaneously 25mg/kg/day of MTX for 1 month. MTX increased norepinephrine and serotonin content in anterior hypothalamus (P < or = 0.05), but decreased serotonin concentration in posterior hypothalamus (P < or = 0.05). MTX diminished serotonin turnover in anterior hypothalamus (P < or = 0.01) and decreased plasma LH (P < or = 0.001) and testosterone (P < or = 0.05) levels but those of FSH remained unmodified. We can conclude that MTX exposure: (1) could exert differential effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence, being the anterior hypothalamus the most sensitive region to the pesticide; (2) could inhibit LH and testosterone secretion without changing FSH; (3) four potential pathways might be involved in MTX effects on testosterone secretion (changing LH secretion; modifying serotonin and norepinephrine at the hypothalamic level; alterating the direct neural pathway between brain and testes; and/or by a direct effect in testes).

Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present. This study was undertaken to evaluate the possible effects of MTX in norepinephrine, dopamine and amino acid contents and serotonin turnover in rat striatum. For this purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day of MTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interest were measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However, the content of serotonin, aspartate, glutamine and taurine was not modified by MTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesis and serotonin metabolism. The inhibitory effect on norepinephrine could be explained, at least in part, by the increase of both GABA and glutamate contents. Further studies are needed to understand the effects of MTX on serotonin. Also a disruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine and GABA emerges.