Simulated conditions of microgravity increases progesterone production in I-10 cells of Leydig tumor cell line.

BACKGROUND: The prospect of long-term residence in outer space is becoming a reality. Previously we found that testosterone secretion and spermatogenesis is reduced in model mice on which the shift of body fluids in space is simulated. The present study examines the effects of the microgravity (muG) environment on steroidogenesis of Leydig cells. METHODS: I-10 cells were cultured for 24 h under a simulated muG environment. Progesterone production was evaluated as steroidogenesis. Western blots of the enzyme, 3betahydroxy dehydrogenase (HSD) as well as of the transcription factors, Ad4bp/SF-1 and DAX-1, the amount of adenosine3',5'-cyclic monophosphate (cAMP) and cell morphology were investigated. The muG environment was simulated using clinostat rotation (CR). Rotational (Cont-1) and stationary (Cont-2) controls always received a regular gravity effect with and without rotatory motion, respectively. RESULTS: Progesterone levels in cells under CR were significantly increased compared with those of both controls. Increased progesterone production was not related to the expression of either of the transcription factors or the enzyme. Although the cytoplasm expanded, the amount of cAMP produced under CR did not significantly differ from that produced under both control environments. CONCLUSIONS: Our findings showed that I-10 cells produced more progesterone under a muG, than under control environments. Since the amounts of 3betaHSD, Ad4bp/SF-1, DAX-1 and cAMP were not altered, the increase in steroid production under CR might be due to the expansion of cytoplasm, where steroidogenesis occurs. Steroidogenesis should be investigated in more detail to predict the effects of outer space on humans.

Human sperm motility in a microgravity environment.

Background and Aims: We carried out clinostat and parabolic flight experiments to examine the effects of a microgravity (µG) environment on human sperm motility. Methods: Semen samples were obtained manually from 18 healthy men (aged 27.4 ± 5.4 years) who had given their informed consent. In clinostat experiments, samples that were left stationary were used as a stationary control. Samples rotated vertically and horizontally were used as a rotation control and a clinostat rotation, respectively. In parabolic flight experiments using a jet plane, sperm motility was compared for each parameter at µG, 1G and 2G. The state of 1G during the flight was used as a control. Sperm motility was determined using an automatic motility analyzer HT-M2030 in a microgravity environment. Results: All parameters of sperm motility tended to be lower in clinostat rotation compared with rotation control at both low-speed and high-speed, but the differences were not statistically significant. In parabolic flight, sperm motility and parameters of linear movement were decreased (P < 0.05). There was no significant difference between µG and 2G, but sperm motility was significantly decreased at µG than at 1G. Conclusions: Our findings suggest that sperm motility is reduced under µG. (Reprod Med Biol 2005; 4: 161-168).

[Male fertility in space].

The effects of simulated microgravity on mammalian reproduction were studied using tail-suspended mice, during parabolic flight in a jet plane and in a horizontal clinostat device. In the tail-suspended mouse, which is a model of the shift of body fluid in a microgravity environment, atrophy of the testis and decrease of serum testosterone level were observed. The sperm motility decreased in the muG condition produced by the parabolic flight. There were no statistically significant differences in the efficiency of achieving normal fertilization in vitro, but there was a statistically significant decrease in the number of embryos reaching the morula and blastocyst stages after 96 hours in culture under clinostat rotation. These results suggest that the process of fertilization in vitro is not sensitive to the gravitational vector. However, the possibility exists that microgravity increases the disturbance of spermatogenesis and sperm motility or the frequency of early embryonic lethality. On the possibility of reproduction in space, there are some problems such as the cosmic radiation besides gravity. It is necessary to carry out further experiments in outer space.

Effect of simulated microgravity on testosterone and sperm motility in mice.

We examined changes in the serum testosterone level and in sperm in the testis and epididymis by using tail-suspended mice, which are a simulation model of the body fluid shift in space, to evaluate the possibility of spermatogenesis failure in space environment. We also studied pathological disorders of the testis in the tail-suspended mice. Tail suspension was imposed with a tail harness to a degree at which the hindlegs of mice did not touch the floor of the housing unit. In control mice, the tail was similarly fixed with a tail harness to impose the same stress, except that a hindleg remained on the floor. Body weight was not significantly different between the 2 groups during 7 days, and testicular weight was significantly different. The testosterone level was significantly lower in the tail-suspended group (0.71 +/- 1.24 ng/mL) than in the control group (2.38 +/- 3.50 ng/mL; P <.05). Microscopy with hematoxylin and eosin (HE) and periodic acid-Schiff (PAS) staining showed a small proportion of seminiferous tubules with impairment of spermatogenic function in the tail-suspended group, and multinucleated giant cells were occasionally noted. Terminal deoxynucleotidyl tranferase-mediated nick end-labeling staining revealed positive cells even in animals in which impairment was considered to be mild based on HE and PAS staining. Many cells showed intense p53 immunostaining compared to the control group, with more intense staining of the nucleus in the tail-suspended group. The proportion of motile sperm was slightly but not significantly reduced in the tail-suspended group. However, the mean movement velocity of the motile spermatozoa was significantly decreased.