Methamidophos neurotoxicity

See also Acetylcholine Methamidophos Neurotoxicity Organophosphates Pesticides. 

A few OP compounds cause delayed neuropathy in vertebrates because they inhibit another esterase located in the nervous system, which has been termed neuropathy target esterase (NTE). This enzyme is described in Chapter 10, Section 10.2.4. OPs that cause delayed neuropathy include diisopropyl phosphofluoridate (DFP), mipafox, leptophos, methamidophos, and triorthocresol phosphate. The delay in the appearance of neurotoxic symptoms following exposure is associated with the aging process. In most cases, nerve degeneration is not seen with initial inhibition of the esterase but appears some 2-3 weeks after commencement of exposure, as the inhibited enzyme undergoes aging (see Section 16.4.1). The condition is described as OP-induced delayed neuropathy (OPIDN). 

Neurotoxic chemicals and motor neuropathy Chlorpyrifos, dichlorvos (DDVP), EPN, n-hexane, 2-hexanone, lead, lead chromate, lead II thiocyanate, leptophos, methamidophos, mipafox, omethoate, parathion, trichlor-fon, trichloronate, triorthocresyl phosphate Neurotoxic chemicals and sensorimotor neuropathy acrylamide, allyl chloride, arsenic and compounds, arsenic trichloride, calcium arsenate, carbon disulfide, dichloroacetylene, ethylene oxide, gallium arsenide, lead arsenate, mercuric chloride, mercuric nitrate, mercurous nitrate, mercury, nitrous oxide, phenyl arsine oxide, thallium and soluble compounds, thallous nitrate... 

Methamidophos can cause delayed neurotoxicity in hens. The NOAEL from a long-term dosing study in rats was 0.03 mg kg day based on brain choli-... 

Seven developmental toxicity studies (four rat, three rabbit) failed to show fetal or embryonic toxicity at doses of methamidophos less than those affecting dams. No evidence was forthcoming from these experiments that there was an increase in sensitivity among fetal/embryonic animals compared with adults. It is therefore unlikely that an additional factor will be required to protect against increased pre-/post natal sensitivity to methamidophos. The recently completed developmental neurotoxicity study of methamidophos also indicates that fetal/young rats are not more sensitive than adults. However, there must remain a degree of uncertainty about the precise dosage received by the pups in the reproductive toxicity and developmental neurotoxicity studies. 

---