Body and organ development of young rats maternally exposed to methadone

The effects of maternal methadone (5 mg/kg methadone-HCl) administration during gestation and/or lactation on gross body measurements, absolute and dry organ weights, and tissue water content were studied in 60-day-old Sprague-Dawley rats. Female offspring perinatally exposed to methadone had body weights and measurements that were comparable to controls, but male rats from each treatment schedule had at least one subnormal body measurement. In contrast to controls, methadone-treated rats had alterations in both wet and dry organ weights, with many organ weights of experimental animals being significantly higher in weight than those of controls. Few differences in tissue water content of any organ were observed between methadone-exposed and control rats. Calculation of organ weight gain from 21 to 60 days of age revealed that methadone-treated animals exhibited abnormally greater weight gains than controls during the postweaning period. These findings suggest that the growth deficits observed at 21 days are, to a large degree, not apparent at sexual maturity. The question of whether this ‘catch-up’ growth is qualitatively as well as quantitatively complete and the implications of these aberrant growth patterns on function needs further evaluation.