Unfortunately, the same end points were not examined 
in ovarian fragments and cultured follicles, no rotational 
control group was included, and the number of repli cates per group and other experimental details were not 
provided.By contrast, exposure to either sim ulated microgravity or simulated hypergravity lengthened 
oestrous cycles due to lengthened dioestrous, whereas 
space flight resulted in cessation of cycling, suggesting 
that other exposures (such as stress or circadian rhythm 
disruption) during space flight besides microgravity 
affect the hypothalamic-pituitary-ovarian axis. By contrast, nearly 40% of 
morula or early blastocyst stage embryos cultured in 
simulated microgravity progressed to the expanded 
blastocyst stage by 48 h. Both simulated microgravity 
and rotational control morula or early blastocyst stage 
embryos had upregulation of SAPK (a stress-activated 
protein kinase) phosphorylation at Thr183 or Thr185, 
a marker for activation of SAPK signalling, after 24h of 
culture compared with static controls; all of these effects 
were similar but less severe in rotation controls than in 
animals in simulated microgravity. As a result 
of the similarity of lengthened vaginal dioestrous during 
microgravity with lengthened vaginal dioestrous dur ing pseudopregnancy in rodents (which is elicited by 
cervical stimulation that causes a surge of prolactin 
secretion), suppression of prolactin secretion was tested 
and found to block the induction of lengthened dioes trous by hypergravity52.Exposure of pregnant rats to hypergravity 
during the second half of gestation did not alter gesta tion length, duration of parturition (time from birth of 
first pup to birth of last pup), litter size or birth weights; 
however, the frequency of lordosis contractions during 
labour decreased by half45 and neonatal pup mortality 
was increased in rats exposed to hypergravity46,59. Oocytes were harvested at the germinal 
vesicle stage (which is the metaphase of the first meiotic 
division) from immature Kunming mice 48h after injec tion of 7.5IU equine chorionic gonadotropin to stimu late development of a cohort of preovulatory follicles.This find ing under microgravity was related to abnormal meiotic 
spindle formation during both the first and second meio tic divisions, with abnormal localization of ?-tubulin 
(which is essential for spindle formation) around the 
chromosomes of oocytes cultured in simulated micro gravity.Exposure of female 
and male mice to hypergravity before mating and 
through gestation decreased pregnancy rates up to 2.9g
(with no pregnancies at 3.5 g), decreased fetal size and 
altered skeletal development (the longest dimension 
of most bones measured was increased at 2.3 g, the longest dimension and perimeter of most bones were 
decreased at 2.6g and these parameters were decreased 
for all bones at 2.9 g) compared with 1 g controls48.Rather, decreased 
neonatal survival of pups born to dams exposed to 
hypergravity was associated with decreased glucose oxi dation and lipogenesis in mammary glands, decreased 
size of adipocytes with decreased rate of lipolysis and 
an increased rate of glucose incorporation into lipids in 
the liver53.Fertilization of mouse oocytes occurred normally 
under microgravity simulated using a 3D clinostat; how ever, continued culture under microgravity resulted in 
delayed development to the blastocyst stage and fewer 
trophectoderm cells in those embryos that reached the 
blastocyst stage compared with embryos at normal grav ity57.No 
differences in mating ability or gestation length were 
observed in rats adapted to hypergravity (2.2g or 3.1g), 
but the number of fetuses and maternal care of pups were 
dose-dependently decreased compared with those of 1g
controls50.In other work, luteal cells from the corpora lutea of 
pregnant rats were cultured in microgravity simulated 
using a high aspect ratio vessel and compared with cells 
from spinner flask controls or in microgravity simulated 
using a clinostat with static controls.Luteal cells cultured in the clinostat model for 2 days 
had increased DNA damage as measured by the Comet 
assay, increased apoptosis and decreased numbers of 
active mitochondria compared with static controls42.In contrast to the abnormal organization of 
microtubules, microfilament organization and function, 
which are necessary for migration of the chromosomes 
and spindles to the periphery of the oocyte, were not 
disrupted under simulated microgravity55.Preimplantation development of 
mouse embryos has also been investigated using a rotary 
cell culture system with high aspect ratio culture vessels 
to simulate microgravity compared with static culture 
controls and rotation controls58.Luteal cells cul tured in both microgravity models exhibited decreased 
progesterone secretion compared with their respec tive control cultures during up to 8 days of culture42,43.Moreover, exposure to hyper gravity for >=8 h during the dioestrous phase of the 
oestrous cycle, but not during other cycle stages, induced 
a surge of prolactin secretion49.