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Tapetal changes in beagle dogs. I. Ocular changes after oral administration of a beta-adrenergic blocking agent--SCH 19927.

SCH 19927 [R,R)-(-)-2-Hydroxy-5-[1-hydroxy-2-[(1-methyl -3-phenylpropyl)amino]ethyl]benzamide hydrochloride) is a beta-adrenergic blocking agent which has vasodilating properties. In a subchronic oral toxicity study in beagle dogs, SCH 19927 was given by gavage at doses of 30, 60, and 90 mg/kg. Lesions were observed at weeks 13 and 19 in the tapetum lucidum, a light reflecting structure of the eye. The lesions consisted of focal to multifocal areas of discoloration of the tapetal portion of the ocular fundus, pigmentation in the tapetal area, and, in one dog, subretinal edema resulting in a focal retinal detachment. Light and electron microscopic examination of the ocular lesions demonstrated tapetal cell degeneration and necrosis with macrophages, lymphocytes, and occasional plasma cells in the tapetum and adjacent choroid. Local cellular infiltrates within the retina internal to the pigmented epithelium were observed in one dog (60 mg/kg) which was demonstrated to have focal retinal edema during the study. In a repeat study the lesion again occurred in tapetal beagle dogs but not in atapetal beagle dogs (90 mg/kg) or cynomolgous monkeys (360 mg/kg). The lesion had not occurred in a previous subchronic study in albino rats. These results demonstrated that the tapetum lucidum was a target organ of toxicity for SCH 19927 and indicated that the finding was without observable toxicological significance in animals, including man, whose eyes do not have this structure.