Chronic phenylmercuric acetate toxicity in a horse
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Abstract:
Phenylmercuric acetate (PMA) was administered orally to a horse over a period of 27 weeks (190 days) at a dose rate of 0.4 mg Hg/kg per day. The effects produced were consistent with those of chronic inorganic mercury intoxication. The clinical features included masseter muscle atrophy, difficulty in prehension and mastication, malodorous breath, reduced appetite and weight loss, and reflected significant pathological changes involving the buccal, mandibular and dental tissues. Renal dysfunction was evident terminally and there was degeration and necrosis of the proximal tubular epithelium. Necrotic and mineralized foci were found in facial and masticatory msucles, splenic trabecuale and the myocardium. The central nervous system and the intestinal tract were unaffected. The approximate mean plasma inorganic mercury concentration was 500 ng/ml whereas organic mercury levels in blood were much lower. The renal cortex had the highest inorganic mercury content, three times greater than in the liver and cecum, while organic mercury was highest in those tissues and absent from the kidney. The difference in the effects produced in this horse as compared to those in a horse receiving mercuric chloride at the same mercury dose rate, could be attributed to the more rapid and complete absorption of PMA from the gastrointestinal tract.
Insights
Phenylmercuric acetate (PMA) caused chronic mercury poisoning in a horse, leading to muscle atrophy and dental issues. Renal dysfunction and tissue damage were observed, with higher inorganic mercury levels in the kidneys.
Area of Science:
- Veterinary Toxicology
- Environmental Health
- Pathology
Background:
- Chronic mercury intoxication poses significant health risks to equines.
- Understanding the toxicokinetics and pathological effects of different mercury compounds is crucial for diagnosis and treatment.
Purpose of the Study:
- To investigate the clinical and pathological effects of chronic oral phenylmercuric acetate (PMA) administration in a horse.
- To compare the toxicological profile of PMA with other mercury compounds.
Main Methods:
- Oral administration of PMA to a horse over 27 weeks at 0.4 mg Hg/kg/day.
- Clinical observation, pathological examination of tissues, and mercury level analysis in plasma and tissues.
Main Results:
- Clinical signs included masseter muscle atrophy, mastication difficulties, weight loss, and dental pathology.
- Pathological findings revealed renal tubular degeneration/necrosis, and necrotic foci in muscles, spleen, and myocardium.
- Mean plasma inorganic mercury was 500 ng/ml; kidneys showed the highest inorganic mercury accumulation.
Conclusions:
- Phenylmercuric acetate induces chronic inorganic mercury intoxication in horses, with significant oral and renal pathology.
- PMA's rapid gastrointestinal absorption contributes to its toxicity, differing from mercuric chloride effects.