Effects of 2.0-g 1.75-g and 1.5-g Hypergravity on Pregnancy Outcome in Rats (Rattus norvegicus)

In 1995, ten pregnant female rats were launched on the Space Shuttle (STS-70) on Gestational day(G) 11 of their 22-day pregnancy as part of the NASA/NIH.Rodent (R)2 Experiment. Following landing on G20, fetuses were harvested from half of the dams, while the remaining five dams underwent birth. Spaceflight did not interrupt pregnancy, alter litter sizes, or affect body weights or gender ratios of the fetuses or neonates. In the present study we used the NASA/NIH.R2 experimental paradigm to analyze the effects of hypergravity on pregnancy outcome. On G10, time-bred Sprague-Dawley rat dams were assigned to either G20 or Birth conditions, then further assigned to Hypergravity (HG) 2.0-g, HG 1.75-g, HG 1.5-g, Rotational Control (RC, 1.03), or Stationary Control (SC, 1.0-g) treatments. Dams were exposed to continuous centrifugation from G11 through G20, with brief daily stops for animal health checks and maintenance. For both the G20 and Birth dams, comparable litter sizes and litter gender ratios were observed across gravity conditions. However, centrifugation-exposed (HG and RC) fetuses and neonates showed significantly lower body masses (p less than 0.05) relative to SC offspring. HG 2.0-g offspring weighed significantly less than those in all other gravity conditions (p less than 0.05). The observed reductions in offspring body mass at 1.5-g and 1.75-g, can be attributed to the rotational component of centrifugation, rather than to increased gravitational load, whereas 2.0-g hypergravity exposure further exacerbated the gravity centrifugation effect on offspring body mass. Pregnant dams exposed to centrifugation weighed significantly less than SC dams (p less than 0.05), suggesting that centrifugation effects on maternal body mass may contribute to reduced size of the developing offspring. These findings are consistent with previous reports of non-pregnant adult animals suggesting that, whereas spaceflight has virtually no effect on body mass, centrifugation is associated with changes in body weight regulation.