RESUMO
A brief historical review is presented concerning comparative studies carried out in the last years on vertebrate antioxidant defenses. In the first part of the article, "Protein-SH: Sugestive remarks", the role of protein thiols is discussed, specially focusing on the function of SH-rich hemoglobins in vertebrates. A functional relationship between animals possessing SH-rich hemoglobins and the ecophysiological characteristics they exbibit related to diving, to high oxygen consumption, and/or to physiological hypoxia during exercise is suggested. The production of reactive oxygen species during hypoxia/reperfusion, or hypoxia alone, and SH activation, are in agreement with the argument that at least part of the thiol groups of SH-rich hemoglobins can act as antioxidant. In the second part of the article, "Comments on antioxidant defenses in fishes and bats", a synthesis of the experiments performed in the last three years is presented. Results were obtained mainly according to new insights emerged from comparative studies conducted in diverse phylogenetic groups of vertebrates. In a first step a correlation between activity level of some marine fish species and atioxidant defenses (AD) was observed; then the AD status was studied in different phylogenetic fish groups. Further experiments were done in a single marine fish species, aiming to demonstrate a relationship between AD and fish ontogeny, and also between fish AD and seasonal changes. It was also demonstrated that fish can get rid of hydrogen peroxide by a single diffusion through the gills. Microchiropteran bats were also analyzed because they experience drastic changes in oxygen consumption due to the torpor nechanism, and also because they are characterized by an unusually high longevity.