Factors that increase endogenous estrogen production or reduce the binding of estradiol to SHBG may increase a woman's risk of developing breast cancer later in life.
. Effects of microgravity or simulated launch on testicular function in rats. J. Appl. Physiol. 73(2}, Suppl.: 174S-185S, 1992.--Testes from flight rats on COSMOS 2044 and simulated-launch, vivarium, or caudal-elevation control rats (5/group) were analyzed by subjective and quantitative methods. On the basis of observations of fixed tissue, it was evident that some rats had testicular abnormalities unassociated with treatment and probably existing when they were assigned randomly to the four treatment groups. Considering rats without preexisting abnormalities, diameter of seminiferous tubules and numbers of germ cells per tubule cross section were lower (P < 0.05} in flight than in simulated-launch or vivarium rats. However, ratios of germ cells to each other or to Sertoli cells and number of homogenization-resistant spermatids did not differ from values for simulated-launch or vivarium controls. Expression of testis-specific gene products was not greatly altered by flight. Furthermore, there was no evidence for production of stress-inducible transcripts of the hsp70 or hspg0 genes. Concentration of receptors for rat luteinizing hormone in testicular tissue and surface density of smooth endoplasmic reticulum in Leydig cells were similar in flight and simulated-launch rats. However, concentrations of testosterone in testicular tissue or peripheral bloodplasma were reduced(P < 0.05}in flight ratsto <20% ofvaluesforsimulated-launch or vivariumcontrols. Thus spermatogenesis was essentially norrealin flight rats, but productionof testosterone was severely depressed. Exposure to microgravity for>2 wk might result in additional changes.Sequelaeof reducedandrogen production associated with microgravity on turnoverof muscle and bone shouldbe considered. (29) concluded that spermatogenesis was not affectedin rats flown 7 or 13 days on COSMOS 1667 or COSMOS 1887. Serum concentrations of testosterone were low in rats after return from spaceflight (11),indicating that endocrine function of the testes might be altered by stressfactorsassociated with spaceflightor effectsof microgravity.The reasons for abnormalities of the endocrine and possibly the exocrine (spermatogenic) functions of the testesassociatedwith spaceflight, at leastin rats,are unknown but could be relatedto altered function of the hypothalamus or adenohypophysis (9),altered fluiddistribution in the body (22),and/or restricted blood and lymph flow within the testis.Startingwith the assumption that stress factorsassociatedwith spaceflight, or effectsof microgravity per se, represent simply a unique set of environmental toxins, we used approaches of reproductive toxicologyand cellularand molecular biology to evaluate testicularfunction in ratsfrom COSMOS 2044. Sensitivemethods forquantification ofalterationsoftesticular functionby enumeration of germ cells,morphometric analyses, and techniques of cellular endocrinology have proven to be invaluable in identifying reproductive toxins (1)(2)(3)17).
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