Male mice of the TO strain were exposed to 50 ATA helium (0.5 ATA oxygen) over 5 weeks and then assessed for fertility both in vitro and in vivo. Significantly lower values for acrosome loss and fertilization of zona intact eggs in vitro were obtained with spermatozoa from the pressure-treated males. These results, coupled with the significant decrease in incidence and degree of polyspermy in zona-free eggs, indicated that fewer competent cells were present after preincubation under capacitating conditions. Fewer motile cells were observed in most samples, along with a reduction in the incidence of hyperactivated motility in some. Testis weight was also significantly lower. Results of fertilization in vivo, after mating with untreated females, showed a consistent trend toward subfertility, with a lower pregnancy rate and a smaller litter size. These differences did not reach significance, however, unlike those obtained in earlier in vivo experiments with males of the BALB/c strain. The discrepancy between in vitro and in vivo results with TO males probably represents differences between unselected and selected sperm populations, while that observed in vivo between the two strains probably reflects the superior reproductive capacity of the TO strain.
Male mice were exposed to 50 ATA heliox pressure to study whether their functional fertility was affected. In series I, control mice were exposed to 1 ATA air; in series II controls were exposed to 5 ATA heliox, which enabled the PO2 and environmental temperature to be maintained at equivalent levels to the pressure group. After exposure during one spermatogenic cycle, the mice were mated with untreated females. There was a dramatic reduction in fertility in the pressure groups, with males in both series I and II showing a 65% reduction in fertility. Overall results were as follows: 19.5% pregnant females mated with the pressure groups compared with 55% pregnant in the control groups. Litter sizes in the pressure groups were reduced by 44%, but there was no evidence of any pressure-related teratological effect. This reduction in fertility appears to be due to high pressure per se and not to the high environmental temperature and PO2 associated with heliox atmospheres.
This study was designed to investigate the mechanism of the subfertility produced when male mice are exposed to high pressure [Baden et al, 1982]. In the first series of experiments, male BALB/c mice were exposed to 50 ATA helium pressure intermittently throughout spermatogenesis (5 weeks). Control mice were exposed to 1 ATA air under identical conditions for an equivalent period. Immediately after exposure half the mice in each group were sacrificed, the remainder being sacrificed 14 days later. Testes were weighed and prepared for histological examination, and spermatozoa were examined for motility and abnormalities. More testes in the pressure group had disorganised seminiferous epithelia and weighed less than the control group; in addition the motility of sperm was also reduced immediately after pressurisation.
In the second series, male mice were exposed to 50 ATA pressure, or 1 ATA air intermittently for only 1 week to assess whether this exposure, for a period sufficient only to affect epididymal sperm, had any effect on functional fertility. The males were subsequently mated with untreated females; no difference was seen between the groups for pregnancy rate, preimplantation loss, or fetal survival.
These data support the idea that the changes in spermatogenesis causing subfertility in mice are fairly subtle, but are consistent with the premature release of spermatids from seminiferous epithelium. Epididymal sperm remained functionally unaffected by exposure to high pressure.
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