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ToxSci Advance Access published online on November 17, 2007
Toxicological Sciences, doi:10.1093/toxsci/kfm286
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Published by Oxford University Press 2007.

Predicting maternal rat and pup exposures: How different are they?

Miyoung Yoon* and Hugh A. Barton{dagger}

* National Research Council Research Associateship Program at U.S. Environmental Protection Agency, Research Triangle Park, NC, USA, yoon.miyoung{at}gmail.com {dagger} National Center for Computational Toxicology, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA

Correspondence: Hugh A. Barton, National Center for Computational Toxicology, B205-1, Office of Research and Development, US Environmental Protection Agency, 109 TW Alexander Dr., Research Triangle Park, NC 27711, USA; E-mail: habarton{at}alum.mit.edu

Received September 17, 2007; revision received November 13, 2007; accepted November 14, 2007


  Abstract

Risk and safety assessments for early life exposures to environmental chemicals or pharmaceuticals based on cross-species extrapolation would greatly benefit from information on chemical dosimetry in the young. Although relevant toxicity studies involve exposures during multiple life stages, the mother's exposure dose is frequently used for extrapolation of rodent toxicity findings to humans and represents a substantial source of uncertainty. A compartmental pharmacokinetic model augmented with biological information on factors changing during lactation and early post-weaning was developed. The model uses adult pharmacokinetics, milk distribution, and relevant postnatal biology to predict dosimetry in the young for chemicals. The model addressed three dosing strategies employed in toxicity studies (gavage, constant ppm diet, and adjusted ppm diet) and the impact of different pharmacokinetic properties such as rates of clearance, milk distribution, and volume of distribution on the pup exposure doses and internal dosimetry. Developmental delays in clearance and recirculation of chemical in excreta from the pup to mother were evaluated. Following comparison with data for two chemicals, predictions were made for theoretical chemicals with a range of characteristics. Pup exposure was generally lower than the mother's with a shorter half life, lower milk transfer, larger volume of distribution, and gavage dosing, while higher with longer half life, higher milk transfer, smaller volume of distribution, and dietary exposures. The present model demonstrated pup exposures do not always parallel the mother's. The model predictions can be used to help design early life toxicity and pharmacokinetic studies and better interpret study findings.

Key Words: early life dosimetry; biological modeling; lactational exposure.


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