Effects Of Simulated Weightlessness By Tail-suspension On Reprodutive Function And HIF-1α Expression In Rat Ovary

Gravity has been a constant physical factor during the evolution and development oflife on Earth. Space flight may induce many of the physiological alterations in variousorgans and systems including fluid shifts, muscle atrophy, bone demineralization, anddepressed cellular immunity due to gravity changes or other conditions such asincreased radiation, noise, isolation, disrupted circadian rhythms. However, there islimited information on the effects of weightlessness affecting the structure and functionof female reproductive system. Reproduction in all animals is a well-adoptedphenomenon within the earth’s gravitational field. Any declination of gravity may havea deep effect on reproduction and development. The most popular ground-based rodentmodel for studying microgravity is Morey-Holton hind limb suspension. Accordingly,the present study was designed to investigate the effects of simulated weightlessnessby tail-suspension on the reproduction function and HIF-1α expression in rat ovary.Morey-Holton suspension model was adopted, and the experiments were performedafter approval by the Hospital’s Ethics Committee. The main content and results are asfollows:1. Twenty-five adult Wistar rats were randomly assigned to5experimental groups:suspended for10d (day),20d,30d,30d plus10d gravity recovery, and0hour(control). The animal’s general condition and the weight of body and sex organs wererecorded. The follicle development was observed by hematoxylin and eosin stain (HE). The proliferation and apoptosis of the granulose cells were detected byimmunohistochemistry. The serum levels of estradio l (E2), progesterone, folliclestimulating hormone (FSH) and luteinizing hormone (LH) were examined byradioimmunoassay (RIA). The results showed that the body weight of the animals wassignificantly decreased on the fifth day of tail-suspension and the fifth day of gravityrecovery respectively. The numbers of total follicles, preantral follicles and antralfollicles were all reduced significantly in the suspended rats, except thegravity-recovery rats, compared with control (P＜0.05). The bromodeoxyuridine (BrdU)and cleaved caspase-3immunohistochemical staining provided the evidence thatsimulated weightlessness by tail-suspension inhibited granulose cell proliferation (P＜0.05) and promoted granulose cell apoptosis (P＜0.05). In addition, simulatedweightlessness increased the levels of serum LH and FSH (P＜0.05) and decreased thelevel of oestradiol (P＜0.05), but had no influence on serum progesterone level.2. The adult female Wistar rats of30-day suspension (n=5) and30-day suspension plus10-day gravity recovery (n=5) were cohabited with the male ones to test the ability andquantity of newborn rats as compared with the corresponding control animals. Thestudy showed that the simulated microgravity by tail-suspension affected thereproductive capacity of rats, and the number of daughter rats were decreased in rats of30-day suspension compared with control group (P＜0.05).3. Sixty adult female Wistar rats were randomly divided into10experimental groups：suspended for6h,12h,24h,2d,3d,5d,7d,14d,21d and0h (control). HIF-1αexpression in rat ovary was detected by using immunohistochemical staining andRT-PCR method. HIF-1α expression could clearly be detected as brown particles in thegranulose cell layer of rat ovary, and was overexpresssed in the nuclear of granulosecells in rat under simulated weightlessness for6hrs and12hrs. The tail-suspension could also significantly increased HIF-1α expression in rat ovary at mRNA level in theearly phase of weightlessness. Both protein and mRNA levels of HIF-1α were declinedand had a trend to normal range during the late phase of sustained suspension.In conclusion, the present study demonstrates the systematical alterations of ovarianstructure and function of rats under simulated weightlessness by using HE,immunohistochemical, RT-PCR and RIA techniques. The experimental findings showthat the simulated weightlessness by tail-suspension inhibites the follicle development,induces the disorder of female hormone secretion, and injuries the reproductive abilityof female rats. The results indicate that the changes induced by microgravity are able torestore to some extent through the recovery of the gravity. In addition, the study alsosuggests that HIF-1α plays important roles in the stress response of ovary to thesimulated weightlessness. Further investigations upon this preliminary study areneeded to clarify the cellular and molecular mechanisms responsible for theweightlessness stress response and to develop effective countermeasures for theastronautess in the weightless tolerance training and spaceflight.