CRITICAL PERIOD OF CARBON TETRACHLORIDE-INDUCED PREGNANCY LOSS IN FISCHER-344 RATS, WITH INSIGHTS INTO THE DETECTION OF RESORPTION SITES BYAMMONIUM SULFIDE STAINING

Several low-molecular weight halocarbons have been shown to cause full -litter resorption (FLR), i.e., pregnancy loss, in Fischer-344 rats tr eated during organogenesis. To determine periods of gestation sensitiv e to acute exposure, a single dose of 150 mg carbon tetrachloride (CCl 4)/kg was administered on gestation day (GD) 6, 7, 8, 10, or 12. Fetus es were delivered by cesarean section on GD 20. Non-gravid uteri were examined for resorption sites, placed in 10% ammonium sulfide, and re- examined for stained resorption sites approximately 1 and 4.5 hr later . FLR was seen in 4% (1/27) of control dams and 36% (4/11), 54% (7/13) , 72% (18/25), 54% (7/13), and 0% (0/12) of dams treated on GD 6, 7, 8 , 10, and 12, respectively. Ammonium sulfide staining clearly yielded a more accurate account of the incidence of FLR. The technique was mos t effective when the staining period was extended to 4.5 hr, as two ca ses of FLR were revealed that had been undetected after 1 hr of staini ng. For dams with FLR, staining was required to detect resorption site s in all dams treated on GD 6 or 7, most dams treated on GD 8, and one dam treated on GD 10. Fewer implantation sites were detected in the d ams treated on GD 6, and the size of the stained resorption sites incr eased as the day of treatment was delayed. These findings demonstrate a relationship between tile time of toxicant exposure and the size and detectability of resorption sites near term, suggesting that the size of the resorption site may reliably reflect the time of embryonic dea th. Treatment on GD 8 caused the highest incidence of FLR and will be used in subsequent mechanistic research. (C) 1997 Wiley-Liss, Inc.