Altered thyroid hormone status and dichlorvos toxicity in rats

Area of Science:

• Toxicology
• Endocrinology
• Biochemistry

Background:

• Serum cholinesterase is a critical enzyme affected by various physiological factors.
• Thyroid hormones play a significant role in metabolic regulation.
• Dichlorvos is an organophosphate insecticide known to inhibit cholinesterase activity.

Purpose of the Study:

• To investigate the influence of altered thyroid function (hypothyroidism and hyperthyroidism) on serum cholinesterase levels.
• To determine the impact of these thyroid alterations on the toxicity of dichlorvos in male and female rats.
• To explore potential sex-specific differences in response to dichlorvos under varying thyroid states.

Main Methods:

• Adult male and female rats were subjected to induced hypothyroidism and hyperthyroidism.
• Serum cholinesterase activity was measured in all experimental groups.
• Dichlorvos was administered orally at a dose of 52.5 mg/kg to assess toxicity and mortality rates.
• Mortality and susceptibility were compared between sexes and thyroid states.

Main Results:

• No significant difference in baseline serum cholinesterase levels was observed between male and female rats.
• Oral dichlorvos administration led to 30% mortality in intact female rats.
• Hypothyroidism significantly increased serum cholinesterase activity, while hyperthyroidism significantly decreased it in both sexes.
• Hyperthyroid female rats exhibited greater susceptibility to dichlorvos toxicity compared to males, despite comparable reductions in serum cholinesterase activity.

Conclusions:

• Thyroid status profoundly modulates serum cholinesterase activity and dichlorvos toxicity in rats.
• While baseline cholinesterase shows no sexual dimorphism, female rats, particularly hyperthyroid ones, are more vulnerable to dichlorvos.
• These findings highlight the complex interplay between endocrine function, enzyme activity, and pesticide toxicity, with implications for risk assessment.