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  • Title: Effects of dietary dieldrin on reproduction in the Swiss-Vancouver (SWV) mouse.
    Author: Birgo BB, Bellward GD.
    Journal: Environ Physiol Biochem; 1975; 5(6):440-50. PubMed ID: 1213033.
    Abstract:
    Reproduction was studied in SWV female mice that had raised one litter and then received either 0.2.5,5,10,15,20 or 25 parts/10(6) dietary dieldrin (n = 18 or 19 per group). Exposure began 4 weeks prior to the second mating and continued until day 28 postpartum (weaning). Fertile males were caged with the females during weeks 5-6 of exposure. Significantly mortality of the females occurred only at 20 and 25 parts/10(6) (89% and 56%, respectively) and all deaths occurred before parturition. Dieldrin did not affect behavioural oestrus. At 10 and 15 parts/10(6), 18% of the bred females did not become pregnant; all animals at lower doses and all survivors at higher doses were fertile. The gestation period was not affected. At 25 parts/10(6), the litter size was decreased by 17% over the control size (13.2 pups). The infertility and reduced fecundity resulted from a lesion(s) preceding implantation. Thus, in a separate experiment, 15 parts/10(6) increased the number of bred females that had no implantation sites 5 days post coitum while 25 parts/10(6) decreased the number of sites per pregnant female. As expected from the original dose-responses for infertility and decreased litter size, the converse effects did not occur. Pre-weaning mortality of all the pups occurred in 31%, 47%, 80% and 100% of the litters at 0,2.5,5, and larger than or equal to parts/10(6), respectively. Within the litters raised at 2.5 and 5 parts/10(6), the pup survival was not different from the controls (75%). Thus, in this strain, litter -oss is dieldrin's most important reproductive effect and it correlated with a dieldrin-induced maternal hepatomegaly. The birth weight of pups in litters that were lost was reduced by 3-13% and pre-death growth was reduced or absent. Pup-killing and pup-neglect were important proximate causes of mortality, but only at doses larger than or equal to 15 parts/10(6). Effects of dietary dieldrin on reproduction in the Swiss-Vancouver (SWV) mouse were investigated. SWV female mice that had raised 1 litter received either 0, 2.5, 5, 10, 15, 20, or 25 parts/million (ppm) dietary dieldrin. Exposure began 4 weeks prior to the 2nd mating and continued until weaning (Day 28 postpartum). During Weeks 5-6 of exposure fertile males were caged with the females. Mortality of the females occurred only at 20 and 25 ppm (89 and 56%) and all deaths occurred before parturition. Behavioural estrus did not appear to be affected by dieldrin. 18% of the bred females did not become pregnant with doses of 10 and 15 ppm but all animals at lower doses and all survivors at higher doses were fertile. Litter size was decreased by 17% at doses of 25 ppm. Infertility and reduced fecundity resulted from lesions preceding implantation. In another study, 15 ppm increased the number of bred females that had not implantation sites 5 days postcoitum while 25 ppm decreased the number of sites per pregnant female. At 0, 2.5, 5, and greater than or equal to 10 ppm preweaning mortality of all the pups occurred in 31, 47, 80, and 100% of the litters, respectively. Pup survival within the litters raised at 2.5 and 5 ppm was similar to that of controls. Pup birth weight in litters lost was reduced by 3-13% and pre death growth was reduced or absent. At doses greater than or equal to 15 ppm pup-killing and pup neglect were important proximate causes of mortality. Litter loss appears to be dieldrin's most important reproductive effect.
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