Hypothalamic and Pituitary Abnormalities

The close neural relationship of the hypothalamus and the pituitary gland with the brain makes them particularly vulnerable to neurotoxins such as the organophosphate pesticides and the heavy metals lead and mercury. Although the numbers of studies on these tissues are few, reflecting their very small size and inaccessibility, there is clear evidence that both these heavy metals, and the organochlorine and carbamate pesticides, can damage the neurones of the hypothalamus which are responsible for GnRH release, leading to failure of ovaries and testes to produce yolky eggs and viable sperm. Organochlorine and organophosphate pesticides, cyanide, PAHs, PCBs, cadmium and mercury can all cause degeneration of the secretory cells of the pituitary gland and decrease its release of hormones.2 Industrial pollutants, such as paper mill effluents, can also affect the responsiveness of the pituitary to GnRH released by the hypothalamus.6 The feedback signal to the pituitary, which regulates plasma steroid hormone balance, can be disrupted by any xenobiotic that has hormone mimicking properties. Organochlorine pesticides, such as the lindane impurity ^-HCH, mimic natural estrogen and induce a negative feedback response in the pituitary.7 This could account for many of the reports of reproductive failure of fish in waters such as the Great Lakes that are heavily polluted with organochlorines.

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