Influence of Age on Delayed Neurotoxicity and Tissue Concentration of Phosvel in Chickens

This study was undertaken to consider the effects of age on the delayed neurotoxicity and tissue distribution caused by the organophosphorus insecticide Phosvel (leptophos). 1. Comparisons were made between 10 young (3-month-old) chickens and 10 adult (23-month-old) chickens which had been given 400mg/kg Phosvel in a single dose. Five chickens were used as controls in each group. The birds were observed daily for mortality and neurotoxic reactions throughout the 28-day test period. Cholinergic toxicity which developed shortly after ingestion was greater in young chickens than in adult, while the reverse was true for delayed neurotoxicity. There was no difference based on age concerning the time required for signs of delayed neurotoxicity to appear. Ataxia in the lower limbs developed between 9 and 13 days after Phosvel administration. The growth rates of young ataxic and paralyzed bird were lower than those of the controls. A sharp weight loss occurred in adult chickens during the time between the onset of ataxia and paralysis. 2. The concentration of Phosvel in various tissues of birds were analyzed by gas chromatography. When the chickens were sacrificed 24hrs after administration, the concentrations of Phosvel in the lungs, liver, breast muscle and brain were less than 1ppm in wet tissue but there were no age differences. Concentrations in wet adipose tissue ranged from 9 to 12ppm. Since the adipose tissue in adult chickens constitutes a large proportion of total body weight than in young chickens the Phosvel content (total Phosvel in adipose tissue/total dose) was in fact, found to be approximately 13 times greater in the former. 3. Chickens were sacrificed 6, 24, 48 and 72hrs after Phosvel administration of 400mg/kg. Phosvel concentration in the brain peaked at 6hrs and then decreased sharply between 24 and 72hrs. Its biological half-life in the brain was 16.7hrs for young chickens and 15.8hrs for adult chickens. The halflife in adipose tissue was 30.1hrs for young chickens and 100.3hrs for adult chickens. 4. In conclusion, there is an age difference in the delayed neurotoxicity of Phosvel after oral administration to chickens. Phosvel content (% of dosage) and the biological half-life in adipose tissue also show the age difference. However, there is no difference in the concentration of Phosvel in brain of young and adult chickens.