Sperm motion predicts fertility in male hamsters treated with alpha-chlorohydrin.

An understanding of the relationship between altered sperm motion and sperm function (fertility) is important when interpreting the biological significance of toxicant-induced changes in sperm velocity in rodent test species. Previous studies showed that a brief (4-day) exposure of male hamsters to the model chemical alpha-chlorohydrin (ACH) results in significant deficits in epididymal and uterine sperm velocity, which are associated with both a delay and a failure of fertilization in vivo. To characterize this effect in terms of fertility, similarly treated male hamsters were bred to untreated females and pups were counted the day before parturition. ACH treatment resulted in a dose-dependent decline in the percentage of sperm-positive females that were pregnant at the end of gestation (100, 78, 67, 22, and 0 where males were treated with 0, 33, 49, 66, and 83 mg ACH/kg/day, respectively). Cauda epididymal sperm from the same males were assayed for motion characteristics using computer-assisted sperm analysis (CASA), and for fertilizing ability in vitro. While the percentage of motile sperm was unaffected by ACH treatment, sperm velocity declined in a dose-dependent manner at all ACH treatment levels. Furthermore, the velocity of sperm from infertile males was shifted downward consistently across the entire velocity distribution. Since treated males tended to either be infertile (no pups) or have near normal litter size, the correlation between sperm velocity and litter size was nonlinear. Therefore, logistic regression models using velocity cut-off values were the most useful models for predicting fertility. These results support the contention that fertility relies on there being a sufficient number of sperm that exceed a velocity threshold. Sperm from treated males were also less likely to support in vitro fertilization (IVF), providing further evidence of impaired sperm function associated with acute exposure to ACH.

Synchronous assessment of sperm motility and fertilizing ability in the hamster following treatment with alpha-chlorohydrin.

To investigate the relationship between sperm motion parameters and fertilizing ability, a model was developed to assess both of these endpoints synchronously using a toxicant that inhibits sperm motion. alpha-Chlorohydrin (ACH) was administered daily for 4 days to male hamsters at 0, 33, 49, 66, and 83 mg/kg body weight. These males were then allowed a 45-minute breeding period with untreated estrus females on the morning of day 5. One hour after breeding, sperm samples were surgically recovered from the uteri of the females for motility analysis. Six hours later, eggs were flushed from the oviducts and evaluated for fertilization. Cauda epididymal sperm were also collected from the males shortly after breeding. Proportions of motile and progressively motile sperm were manually quantified, and overall sperm velocity and the velocity of representative vigorously swimming sperm in both the uterine and epididymal samples were measured by computer-aided sperm analysis. Significant decreases in in vivo fertilization rates and epididymal sperm motion parameters were observed at 66 and 83 mg/kg ACH, whereas uterine sperm motion was adversely affected at all ACH dosages used. All sperm motion parameters except the percentage of motile sperm in the epididymis were significantly correlated with fertilization rates by both linear and logistic regression. Overall, uterine and epididymal sperm endpoints predicted fertilizing ability comparably well. Stepwise multiple linear regression gave a model containing epididymal sperm velocity (EVCL) and uterine sperm percent motility (UMOT) with an R2 value of 0.649. Stepwise multiple logistic regression gave models containing EVCL alone and EVCL and UMOT in binary (fertile/infertile) and quantal models, respectively.

Acute exposure of female hamsters to carbendazim (MBC) during meiosis results in aneuploid oocytes with subsequent arrest of embryonic cleavage and implantation.

A single oral dose of the fungicide and microtubule poison, MBC, administered to female hamsters at proestrus, results in infertility and early pregnancy loss (1). To characterize the site and mode of action of this effect, direct assessments of oocyte chromosomes, fertilization, and preimplantation embryo development were made. Female hamsters were given a single dose of MBC (1,000 mg/kg) on the afternoon of proestrus (to coincide with meiotic maturation of the oocytes) and either killed shortly after ovulation (day 1) to recover oocytes, or bred and killed on gestation day (gd) 1 to 5 of pregnancy to assess fertilization and preimplantation embryo development and enumerate early implantation sites. Chromosome analysis in unfertilized oocytes revealed an MBC-induced increase in aneuploidy (37 vs. 14% in controls). When animals were bred after dosing, MBC had no effect on the number of oocytes recovered or fertilized. However, significant increases were found in the proportion of embryos that failed to reach the expected stage of development, namely, the eight-cell stage on the afternoon of gd 3, the morula stage by the morning of gd 4, and the blastocyst stage by the afternoon of gd 4 (a time when some embryos have implanted). The mean number of implantation sites, revealed by Evans Blue staining, was also significantly lower in treated females on the afternoon of gd 4 and the morning of gd 5. These simple direct assessments elucidated a mechanism of MBC-induced early pregnancy loss, induction of aneuploidy in oocytes. They also ruled out an effect on fertilization, but demonstrated a subsequent arrest of preimplantation embryonic development accompained by a decrease in the likelihood of implantation.