The effects of stress on the levels of TGO (Glutamic Oxalacetic Transaminase), leukocyte formula and histological changes in brain and heart of Rattus novergicus variety Sprague Dawley variety were evaluated. The experimental evaluation was carried out in the Laboratory of Animal Physiology of the Academic Department of Biology of the UNSA-Arequipa, during the months of November 2015 to January 2016. 24 Rattus novergicus Sprague Dawley variety assigned in four groups were used: T1 (control group , away from any stimulus that disturbs them), T2 (presence of predators for 20 min./day/day cycle), T3 (presence of predators for 20 min./day / night cycle), T4 (presence of predators for 20 min ./every 7 days / day cycle), for 4 weeks. It was shown that stress causes a statistically significant increase in blood TGO levels in rats, compared to baseline levels, but there is no significant differe...