Abstract
Tears are an important component of the ocular surface protection mechanism and are in close contact with the corneal epithelium and the environment. Their composition is well-known in humans; however, there are few investigations on the composition and function of tears in reptiles, birds and others mammals, which would elucidate the mechanisms governing the maintenance of ocular homeostasis. In this work, electrophoretic profiles and an evaluation of total protein, albumin, urea, glucose, and cholesterol concentrations in tears of semi-aquatic, terrestrial, and marine reptiles (Caiman latirostris, Chelonia mydas, Caretta caretta, Eretmochelys imbricata, Lepidochelys olivacea, and Chelonoidis carbonaria), birds (Tyto furcata, Rupornis magnirostris and Ara ararauna), and mammals (Equus caballus and Canis lupus familiaris) were apresented. Human tear components and respective blood serum samples were used as references. The electrophoretic analysis revealed similarities whithin same Classes. The results of the tear–blood serum relationship and the comparison to human tear components showed particularities that are potentially derived from a homeostatic response to the environment. When the tear compositions of animals belonging to different ecological clusters were compared, marked differences were observed in total protein and urea concentrations. Thus, reptile, bird, and mammalian tears are complex fluids with differing concentrations of biochemical components that are potentially a result of the animals' adaptation to different environments.
Highlights
The ecomorphological design of the vertebrate eye reflects the characteristics of the species’ environment and lifestyle [1, 2] and the morphological aspects of the eye are similar for all vertebrates, its microstructural and molecular features vary among species from different ecological niches [3,4,5,6]
Carbohydrates, proteins, electrolytes, metabolites, and hormones [19, 20] and these compounds participate in the transport of other molecules, maintain the stability of the ocular surface, promote adherence and induce a protection mechanism against pathogens [16,17,18]
Human tear and serum samples were collected from 5 women and 5 men, aged 25–45 years, with normal values of tear production and no ocular surface abnormalities as shown by slitlamp biomicroscopy (Kowa Company R, Torrance, CA)
Summary
The ecomorphological design of the vertebrate eye reflects the characteristics of the species’ environment and lifestyle [1, 2] and the morphological aspects of the eye are similar for all vertebrates, its microstructural and molecular features vary among species from different ecological niches [3,4,5,6]. Tears are important components of the ocular surface, and are produced by different animals, from fish to mammals [6, 7, 10] They protect the eye from external damage and help maintain corneal and conjunctival health by preventing dryness and promoting tissue cooling [11,12,13,14,15,16]. They can be considered an interface between the environment and the ocular surface that. Carbohydrates, proteins, electrolytes, metabolites, and hormones [19, 20] and these compounds participate in the transport of other molecules, maintain the stability of the ocular surface, promote adherence and induce a protection mechanism against pathogens [16,17,18]
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