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Comparison of Birth-and Conception-Based Definitions of Postnatal Age in Developmental and Reproductive Rodent Toxicity Studies: lnfluence of Gestation Length on Measurements of Offspring Body Weight and Puberty in Controls
Citation:
NAROTSKY, M. G. Comparison of Birth-and Conception-Based Definitions of Postnatal Age in Developmental and Reproductive Rodent Toxicity Studies: lnfluence of Gestation Length on Measurements of Offspring Body Weight and Puberty in Controls. Presented at Teratology Society Annual Meeting, San Diego, CA, June 25 - 29, 2011.
Impact/Purpose:
Two of these studies defined PND 0 as the DOB; the other studies defined PND 0 to coincide with gestation day (GO) 22. Litters were examined at birth and at various times postnatally.
Description:
Most laboratories conducting developmental and reproductive toxicity studies in rodents assign age by defining postnatal day (PND) 0 or 1 as the day of birth (DOB); i.e., gestation length affects PND and the timing of postnatal measurements. Some laboratories, however, define age based on a particular day of gestation; i.e., PND is standardized by time postcoitus, independent of gestation length. Here, where possible, both approaches were applied retrospectively to control data to assess body weight and pubertal measurements independent of treatment effects. Analyses focused on the influence of gestation length on these endpoints.. Data from four reproductive toxicity studies using Sprague-Dawley rats were examined. Two of these studies defined PND 0 as the DOB; the other studies defined PND 0 to coincide with gestation day (GO) 22. Litters were examined at birth and at various times postnatally. Weanlings were maintained past puberty and examined for onset of vaginal opening (VO) and preputial separation (PPS). All control litters were delivered on GD 21 (n=53) or 22 (n=44). Using OOB-based age, animals born on GD21 remained significantly lighter than GD22-born counterparts at all time points examined, from birth to PNO 38 in females and PI\JD 46 in males (p<0.004 for all DOB-based pup weight analyses; p