Efficacy of trimedoxime in mice poisoned with dichlorvos, heptenophos or monocrotophos.

The aim of the study was to examine antidotal potency of trimedoxime in mice poisoned with three direct dimethoxy-substituted organophosphorus inhibitors. In order to assess the protective efficacy of trimedoxime against dichlorvos, heptenophos or monocrotophos, median effective doses and efficacy half-times were calculated. Trimedoxime (24 mg/kg intravenously) was injected 5 min. before 1.3 LD50 intravenously of poisons. Activities of brain, diaphragmal and erythrocyte acetylcholinesterase, as well as of plasma carboxylesterases were determined at different time intervals (10, 40 and 60 min.) after administration of the antidotes. Protective effect of trimedoxime decreased according to the following order: monocrotophos > heptenophos > dichlorvos. Administration of the oxime produced a significant reactivation of central and peripheral acetylcholinesterase inhibited with dichlorvos and heptenophos, with the exception of erythrocyte acetylcholinesterase inhibited by heptenophos. Surprisingly, trimedoxime did not induce reactivation of monocrotophos-inhibited acetylcholinesterase in any of the tissues tested. These organophosphorus compounds produced a significant inhibition of plasma carboxylesterase activity, while administration of trimedoxime led to regeneration of the enzyme activity. The same dose of trimedoxime assured survival of experimental animals poisoned by all three organophosphorus compounds, although the biochemical findings were quite different.

Efficacy of dietary protein in alleviating toxicity of monocrotophos in rats.

Monocrotophos administration at intervals induced variable responses in phosphatases, transaminases and aldolase of liver and plasma. Hepato-toxicity was aggravated under protein deficient state. A weak resistance to toxicity was observed in rats on low protein diet (5%). However, animals fed on protein enriched diet (20%) indicated an elevation in tissue defense mechanism and were able to combat toxic stress of monocrotophos, though partially. A higher protein level may prove efficient and significant for alleviating pesticide toxicity.

Insights into the mechanisms mediating hyperglycemic and stressogenic outcomes in rats treated with monocrotophos, an organophosphorus insecticide.

The present investigation provides mechanistic insights into the hyperglycemic and stressogenic effects of monocrotophos, an organophosphorus insecticide. Pre-treatment of rats with mifepristone (glucocorticoid receptor antagonist) prevented induction of liver tyrosine aminotransferase activity (TAT), but was ineffective in attenuating hyperglycemia induced by monocrotophos. Pre-treatment with propranolol (ß-adrenergic receptor antagonist) and phentolamine (α-adrenergic receptor antagonist) were effective in abrogating monocrotophos-induced hyperglycemia. Interestingly, while propranolol offered partial protection against hyperglycemia, phentolamine completely abolished the same. However, monocrotophos-induced hyperlactacidemia was completely abolished by propranolol. Both the adrenoreceptor antagonists, however, failed to attenuate the stressogenic potential of monocrotophos. Hyperglycemia and hyperlactacidemia induced by monocrotophos were abolished by pre-treatment with atropine. Exogenous epinephrine was associated with hyperglycemia and hyperlactacidemia. The impact of adrenergic antagonists on epinephrine-induced hyperglycemia and hyperlactacidemia were remarkably similar to that of monocrotophos-induced hyperglycemia and hyperlactacidemia. Further, hydrazine sulfate (a gluconeogenesis inhibitor) abolished hyperglycemia in monocrotophos-treated rats. From our data, it can be hypothesized that excessive stimulation of adrenoreceptors, probably elicited by increased plasma epinephrine, mediates hyperglycemic outcomes induced by monocrotophos. Pattern of changes in plasma lactate suggests that ß-adrenergic activation mediates monocrotophos-induced hyperlactacidemia, while α-adrenergic receptor mediates lactate utilization, leading to hyperglycemia. Induction of liver TAT activity is attributable to glucocorticoid receptor activation as a result of hypercorticosteronemia.