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Male Reproductive Status in Rats is Unaltered Under Continuous Long Term Artificial Gravity (AG).  J.S. Tash1, S. Wolfe1, B.D. Timmerberg1, L.A. Baer2, 1Dept. of Molecular & Integrative Physiology, University of Kansas Medical Center, Kansas City, KS; 2Wyle Laboratories, NASA/Ames Research Center, Moffett Field, CA

    The Bioastronautics Critical Path Roadmap (BCPR) risks include “unacceptable levels of increased hereditary, fertility, or sterility risk caused by occupational radiation exposure or the combined effects of radiation and other space flight factors.”  One potential countermeasure to the effects of microgravity (µG) is artificial gravity (AG) using centrifugal forces.  Sexually mature male rats were maintained for 6 weeks at 2G (AG) in the NASA/ARC 24ft centrifuge facility.  Stationary controls (SC) were pair-fed to the AG animals.  A group of ad lib fed vivarium controls (VC) was maintained for the same period. At the end of 6 wks, half the animals were sacrificed to obtain testes for histology and blood for hormone analysis. The remaining animals were subjected to mating trials to determine whether fertility had been affected by the continuous AG treatment.  Immediately at the completion of the AG exposure, testis weights were significantly greater (as % of whole body weight) in the AG group versus the SC and VIV groups.  In the mating trials, all treatment groups were fertile.  Similar to the increase in testis weight of the AG group, there was a significant increase (+1.4, P<0.02) in the number of pups per litter produced by the AG group versus SC. No other parameters of fertility were different between any of the treatment groups.  By the completion of the mating trials (11 wks after terminating AG), the difference in testis weight had disappeared between the groups. The testis weight and litter findings are particularly interesting in that they are consistent with the hypothesis that biologic systems respond to gravitational forces along a continuum.  In this case, increased gravity produced an increase in litter size and testis weight whereas we previously reported that simulated long term µG, using the hindlimb suspension model, produced sterility and a decline in testis weight.  These results also provide preliminary data for AG as a potential countermeasure for male infertility problems associated with µG.  However, the radiation exposure issue in regard to testicular cancer risk is another problem that will require additional environmental (shielding) and pharmacologic interventions.  (Supported by NASA and NIH).