Background: Weightlessness has different effects on human physiology. Microgravity causes major changes in various body systems in space; like changes in function of sexual system and the secretion of hormones. This study aimed to evaluate the effect of microgravity on the levels of testosterone and LH in rats.

Materials and methods: This experimental study was conducted on 14 adult male rats (race Wistar, the age of about three months, and their weight was approximately 250 grams) that were divided into two groups: control (kept in regular cages) and intervention (in hind limb Plexiglas cages). The dark-light cycle was scheduled 12 hours lightness (about 30 lux) followed by 12 hours darkness. For all rats, the levels of testosterone and LH were measured on days zero and 14. The gathered data were analyzed by SPSS software.

Results: At the baseline of the study, the mean value of testosterone was 1.038±0.08 in both groups and the mean value of LH was 5.15±0.62 and 5.40±0.24 in control and intervention groups, respectively (p>0.05). After 14 days, the level of testosterone was 1.04±0.07 in control group and 0.74±0.09 in intervention group (p<0.05). However, the level of LH was 5.43±0.28 in control group and 6.55±0.31 in intervention group (p<0.05).

Conclusion: In the intervention group, the level of testosterone decreased, while the level of LH increased. It indicates that microgravity only affected testis and pituitary function remained normal. According to these finding, we may adopt appropriate treatment to prevent further damages to astronauts during spaceflight.