Introduction: Aquaporin5 (AQP < sub>5) is an integral membrane protein that plays an essential role in the movement of water in the respiratory system. Under physiological stress such as sports, AQP < sub>5 could change the pulmonary fluid balance and affect gas exchange and lung functions. The purpose of this study was to evaluate the effect of taper program on AQP < sub>5 levels in the lung of male Wistar rats.

Methods: 40 Newborn five-week old male Wistar rats with an average weight of 68±9 g were randomly divided into three groups including the base, control and training groups. The experimental group received a six-week interval exercise while the control group rat remained inactive. At the end of six weeks, the rats were divided experimental and control groups and the arts in the experimental group entered taper program. The Interval Training group ran on treadmill for 6 weeks (6 sessions, 30 minutes each session at a speed of 25 to 70 meters per minute) and then the taper group did so for three weeks in a pattern of decreasing frequency. AQP < sub>5 levels were measured by ELISA methods. Analysis is done with two-way ANOVA and LSD test at P<0.05. To analyze the date, two-way ANOVA as well as LSD test were used at .0.5 level of significance.

Results: The results showed significant increase (P ≤0.001) in AQP < sub>5’s pulmonary tissue  levels of the two-week taper and three-week taper groups compared with the control group, while there no significant difference (P≥0.55) was found between AQP < sub>5 levels in the two weeks taper compared with three-week taper group. Also, up to 73/03 increase was found in the AQP < sub>5 levels of taper group compared to the interval group.

Conclusions: The findings indicate that a period of reduced training with increased levels of AQP < sub>5 may regulate factors involved in pulmonary water balance and reduce injury to epithelial and respiratory tract