Ultimately, successful reproduction is the production of viable progeny. In only one study was mating capability in the space environment examined. Rats were described as having mated successfully in hypogravity, although no viable progeny were produced. It is unclear from the study design whether reproductive effects occurred in the males, the females, or both. Male spaceflight rats mated 5 days after flight to nonflight female rats bred successfully, but their offspring showed growth retardation and more frequent abnormalities, such as edema, hemorrhages, hydrocephaly, ectopic kidneys, and enlargement of the bladder.
Male progeny also showed reduced epididymis weight at 30 days of age, although this reduction did not persist into adulthood (100 days of age). However, male rats mated 2.5-3 mo after spaceflight produced healthy, viable offspring. Santy et al. suggested that spaceflight produced abnormalities in mature sperm but had no effect on early stage sperm. Anecdotal evidence indicates that male astronauts produce healthy offspring following spaceflight. To our knowledge, fertility following recovery from HLS has not been explored. The effect of hypergravity on fertility was investigated by exposing jointly caged male and female rats to chronic centrifugation (2.3 g). Results indicated some reduction in pregnancy rate at 2 g and no successful pregnancies at 4.7 g, an extremely high gload. Megory et al. observed prolonged diestrus in centrifuged rats. Changes in the ovulatory cycle can compromise fertility. Reports of reduced T in centrifuged male rats can also compromise fertility because T is important for maintaining reproductive organ function and spermatogenesis. Whether long-term exposure to altered gravity can lead to subfertility or even infertility and whether effects are temporary or permanent are important questions that must be answered before long-term habitation of space is attempted.