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Models to Study Gravitational Biology of Mammalian Reproduction

Abstract

Mammalian reproduction evolved within Earth's 1 g gravitational field. As we move closer to the reality of space habitation, there is growing scientific interest in how different gravitational states influence reproduction in mammals. Habitation of space and extended spaceflight missions require prolonged exposure to decreased gravity or hypo-gravity (i.e. weightlessness). Lift-off and re-entry of the spacecraft are associated with exposure to increased gravity or hyper-gravity. Existing data suggest that spaceflight is associated with a constellation of changes in reproductive physiology and function. However, limited spaceflight opportunities and confounding effects of various non-gravitational factors associated with spaceflight (i.e. radiation, stress), have led to the development of ground-based models for studying the effects of altered gravity on biological systems. Human bed rest and rodent hindlimb unloading paradigms are used to study exposure to hypo-gravity. Centrifugation is used to study hyper-gravity. In this paper, we review the results of spaceflight and ground- based models of altered gravity on reproductive physiology. Studies utilizing ground-based models that simulate hyper- and hypo-gravity have produced reproductive results similar to those obtained from spaceflight and are contributing new information on biological responses across the gravity continuum, thereby confirming the appropriateness of these models for studying reproductive responses to altered gravity and their underlying mechanisms. Together, these unique tools are yielding new insights into the gravitational biology of reproduction in mammals.