Perinatal methadone exposure in rats. Effects on body and organ development.

The effects of maternal methadone (5 mg/kg methadone-HCl) administration during gestation and/or lactation on gross body measurements, absolute organ weights, dry weights, and tissue water content were studied in 21-day-old Sprague-Dawley rats. Offsprings perinatally exposed to methadone had significantly lower body weights, crown to rump lengths, tail lengths and head diameters. In contrast to age-control values, absolute organ weights of the adrenals, brain, heart, kidneys, liver, lungs, muscle, and testes were reduced in all drug-treated groups; the spleen, thymus, and ovaries of some methadone groups were also lighter in weight. Organ:body weight ratios revealed fewer significant differences than recorded for absolute weights. Dry weights and tissue water content of the kidneys, liver and muscle were affected in all drug-treated animals; other organs were markedly affected by at least one schedule of methadone administration. These results suggest that perinatal methadone exposure has detrimental effects on preweaning organ and body development that may be of long-term functional consequence to the animal.