Effects of prenatal morphine treatment of rats on mortality, bodyweight and analgesic response in the offspring

Abstract

A method is presented for the maternal ingestion of morphine in rats in order to investigate morphine's prenatal effects. Effects on the offspring of the treatment throughout pregnancy were compared with effects of treatment during specific periods of the pregnancy. Morphine treatment (25 mg/kg per day) throughout pregnancy resulted in 0% survival of the offspring. Morphine treatment up to gestational day 21 resulted in 65.4 ± 7.7% survival of the offspring, and up to gestational day 17 in 31.8 ± 13% survival. Reduction in the neonatal birth weight was maximal in animals treated with 25 mg/kg of morphine per day from gestational day 4 throughout pregnancy. The analgesic effect of morphine in the offspring was tested with the hot plate method. Male offspring treated with morphine from gestational day 1 to day 17 showed an elevated thermal response after morphine injections on day 80–90 post partum. These findings indicate a long-lasting, post-partum alteration in that part of the opiate system involved in the perception of noxious stimuli.