Species differences in tears; Comparative investigation in the chimpanzee (Pan troglodytes)

This paper describes evolutionary divergence in composition of tear fluid among some mammals, and discusses the implications of these differences with regard to the choice of appropriate animals for use as models in ophthalmic research. For the first time a comprehensive investigation of tear fluid in the chimpanzee (Pan troglodytes) is presented in which tear fluid was collected during narcosis of eight chimpanzees. Total protein in chimpanzee tear fluid (8.8±0.3 g/l) is not significantly different from total protein of human tear fluid (10.0±0.6 g/l). The values in tear fluid for lysozyme (6.2±1.5 mg Hen Egg Lysozyme, HEL/ml), peroxidase (115±18 U/ml), and amylase (3.5±0.4 U/ml) in chimpanzees were significantly different from those of human lysozyme (11.8±1.6 mg HEL/ml), peroxidase (70±5 U/ml), and amylase (1.0±0.2 U/ml). Polyacrylamide gelelectrophoresis of tear fluid of the chimpanzees shows in comparison with human tear fluid an additional low-molecular protein (<14 kiloDalton).