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Toxicity of methylmercury: effects on different ages of rats
Abstract:
LD50 of methylmercury chloride has been shown to be dependent on the ages of the rats. As the age increases, the LD50 decreases, i.e. the younger rats could tolerate higher doses of methylmercury than the older one. The LD50 were 39.6 +/- 2.3, 33.1 +/- 2.1, 30.3 +/- 1.0, 27.1 +/- 1.0, 24.7 +/- 1.5 and 23.9 +/- 1.1 mg Hg/kg for the 200 g, 300 g, 350 g, 400 g, 450 g and 500 g rates respectively. The elimination of mercury from blood showed little correspondence to age during the 30 days duration. The onset of neurological symptoms after receiving 25 mg Hg/kg of methylmercury chloride occurred between 8 to 15 days post dosing in the surviving rats. Rats unaffected during the latency period did not show neurological signs if their blood-mercury levels decreased to below 100 ppm. Young and old rats showed marked differences in the distribution of mercury in the blood. In the erythrocyte membrane, the eight week old rats retained a higher concentration of the toxic metal than did the 19.5 week old rats. Also, there was significant differences in the ratios of mercury content in the red blood cells to that of plasma; young rats showing 115:1 and for the old ones being 5:1. The permeability of erythrocyte membrane to mercury might play an important role in the age factors on the suceptibility of methylmercury intoxication.
Insights
Younger rats tolerate higher methylmercury chloride doses than older rats, with age significantly impacting LD50 values. Mercury distribution in blood, particularly erythrocyte membranes, differs between age groups, influencing intoxication susceptibility.
Area of Science:
- Toxicology
- Environmental Health
- Pharmacokinetics
Background:
- Methylmercury chloride is a potent neurotoxin.
- Age is a known factor influencing susceptibility to chemical toxicity.
- Understanding age-dependent toxicity is crucial for risk assessment.
Purpose of the Study:
- To investigate the influence of age on methylmercury chloride toxicity in rats.
- To determine the relationship between rat age and LD50 values.
- To explore age-related differences in mercury distribution and elimination.
Main Methods:
- Determined LD50 values for methylmercury chloride across different rat ages (200-500g).
- Monitored mercury elimination from blood over 30 days.
- Analyzed mercury distribution in blood components (erythrocytes, plasma) and onset of neurological symptoms.
Main Results:
- LD50 decreased significantly with increasing rat age, indicating higher susceptibility in older rats.
- Mercury elimination showed minimal age correlation over 30 days.
- Younger rats exhibited higher mercury concentrations in erythrocyte membranes and a greater red blood cell to plasma mercury ratio (115:1 vs. 5:1).
Conclusions:
- Rat age is a critical determinant of methylmercury chloride toxicity, with younger rats tolerating higher doses.
- Differences in mercury distribution, particularly erythrocyte membrane binding and red blood cell partitioning, are key factors in age-dependent susceptibility.
- Erythrocyte membrane permeability to mercury may play a significant role in methylmercury intoxication severity across different age groups.