Effects of chronic morphine administration on pregnant rats and their offspring

The effect of chronic maternal morphine exposure on conception, pregnancy, and perinatal development was studied in rat. Beginning 5 days prior to mating and continuing through gestation and lactation, female Sprague-Dawley albino rats received twice daily intraperitoneal (i.p.) injections of morphine sulfate; drug dosages were gradually increased from 10 mg/kg/injection to a maintenance level of 40 mg/kg/injection. Throughout gestation, drug-treated mothers weighed less than saline-injected controls. Control females displayed progressive weight loss during lactation; morphine injected females showed marked weight gain in the 2nd and 3rd weeks of this period. Morphine administered during pregnancy produced decreased litter size, increased number of stillborns, increased infant mortality, and retardation of body growth in drug-exposed offspring. Weight deficits persisted in young rats observed 5 1/2 weeks after cessation of drug exposure as well as in animals continuing to receive twice daily i.p. injections of 20 mg/kg.