Abstract:
The hypothesis of this project was that extended exposure to microgravity has a negative impact on the ability of the male
mammalian species to reproduce. Previous research showed that simulated microgravity using hindlimb unloading (HLS) for six wks leads to blockage of spermatogenesis and permanent sterility in adult male rats. Additionally, the exposure to HLS leads to a decline in testicular function causing massive apoptosis of the germinal epithelium. The goal of this project was to
determine the maximum duration of HLS that allows for a subsequent restoration of spermatogenesis and fertility. Sexually
mature male rats underwent partial inguinal ligation to prevent the testes from becoming abdominal during HLS. Control
animals (TO) were pair fed to the HLS group and also ligated and harnessed, but the hindlimbs maintained contact with the
floor. Additionally, a group of free roaming control animals (FRC) was analyzed. Animals were exposed to HLS, TO, and
FRC treatment for 4, 5, and 6 wks. Hormone levels of testosterone, FSH, LH, and corticosterone were determined, and as in
previous studies, none of the hormone levels were significantly different in the treatment groups. However, there was a
significant spike in spermatogenic cell apoptosis at 6 wks, indicating that losses of spermatogenesis were beginning. In this
experiment, no significant difference in testis or epididymal weight was noted with time (ANOVA). Since these animals were
younger than in previous studies, we conclude that there may be an age-related sensitivity of the testis in the HLS model.
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