[Can a tail-suspension model be applied to simulate the reproduction system under weightlessness?]

A tail-suspension model to simulate weightlessness is widely used for studies on physiological changes not only of the musculoskeletal system but also of the cardiovascular system. In the present study, we applied this model to investigate whether or not it is possible for male spermatogenesis to occur, and for female rats to maintain pregnancy in this model. Two male rats were suspended with the right inguinal canal ligated loosely for 14 days, and female rats were suspended after copulation (the day when spermatozoa were identified on a smear from the female rat, was referred to as Day 0 for her in this paper). The duration of suspension was chosen dependent upon events to be confirmed during the course of pregnancy. To demonstrate the effects of suspension on implantation, the first and second groups consisted respectively of non-suspended rats penetrated at the base of the tail in the same way as suspended rats, and rats suspended during the former half of pregnancy (Days 0-12, and 0-14). The third group consisted of rats suspended during the latter half (Days 10-20, 10-21, 10-26, and 10-28), and in the final group a rat suspended throughout pregnancy (Days 0-22) was placed. Histological analysis of the male rat testes showed that the testes on the ligated side were scarcely impaired, while the others became degenerated presenting similar appearances of cryptorchidism. The levels of serum testosterone were lower than the control values. As for the female rats, one animal in the final group was successful in parturition, and implantation appeared to be delayed in the second group. A tail-suspended rat, if it is acclimatized to its environment, could succeed in parturition. By employing this model, we can certainly elucidate some new aspects of mammalian reproduction in space.