Reports
Study on Zinc pyridinethione Retinopathy in Laboratory Animals
1989 Volume 8 Issue 1-2 Pages 39-46
Details
1989 Volume 8 Issue 1-2 Pages 39-46
Zinc pyridinethione (ZPT) was orally administered to laboratory animals (a cynomolgus monkey, beagles, a cat, pigmented and albino guinea pigs, and Mongolian gerbils). The time course of ZPT retinopathy was observed by opthalmological procedures.
Animals without the tapetum lucidum (the cynomolgus monkey, pigmented and albino guinea pigs, and Mongolian gerbils) failed to develop ZPT retinopathy. Administrations of 15mg/kg body weight ZPT 3 days a week for 5 consective weeks to the cat induced discoloration of the tapetum lucidum and decrease in amplitude of “a” and “b” waves in the electroretinogram (ERG). In dogs three dose levels of ZPT, 2.5, 5, and 10mg/kg were selected by reference to the results of previous studies. They showed bilateral ophthalmological abnormalities at all doses.
At 10mg/kg of ZPT, only mild changes in the fundus were observed in 24-month-old dogs, which were less sensitive to ZPT than younger dogs.
The changes recognized in these dogs included discoloration of the tapetum lucidum and a slight decrease in amplitude of “a” and “b” waves in the ERG. No histopathological changes were observed in the tapetum lucidum.
Twelve-month-old dogs treated with 5mg/kg ZPT 5 days a week showed subretinal edema and retinal hemorrhage in the fundus and decrease in amplitude of “a” and “b” waves in the ERG.
At increasing dosage from 2.5mg/kg to 5mg/kg of ZPT, lateral geniculate body nucleus (LGN) evoked potentials and visual evoked potentials (VEP) were recorded in animals in which stainless steel electrodes had been implanted in the LGN and the skull. Dosage of ZPT increased from 2.5mg/kg to 5mg/kg induced decrease in amplitude of the ERG, followed by abnormalities of LGN evoked potentials and VEP.
Ophthalmological observation disclosed discoloration of the tapetum lucidum. Histopathological observation revealed thinning of the tapetum lucidum, and electron microscopic observation showed enlargement of the rough endoplasmic reticulum of the tapetal rods in one of the severely affected dogs.
