Effect of maternally administered opiates on the development of the beta-endorphin system in the offspring.

Pregnant rats received subcutaneous implantation of either morphine or placebo pellets at various stages of gestation. Untreated animals served as basic controls. The effect of morphine treatment on the growth of the offspring as well as on the ontogeny of beta-endorphin in the pituitary gland and the hypothalamus was investigated. Results obtained indicated that pregnant rats treated with morphine from day 1 of pregnancy to day 21 presented complete resorption. Subcutaneous implantation of a morphine pellet on days 11, 13 and 19 of gestation allowed pregnancy to term, however the post-natal mortality rate was very high. Implantation of a morphine pellet on days 9 and 13 of gestation allowed pregnancy to term and after birth the withdrawal reaction of the offspring was mild and the mortality rate was low. At early stages of development there were differences in the pituitary and hypothalamic beta-endorphin content between the offspring of the morphine treated animals and the offspring of the control animals, but by day 22 no significant differences among the various groups were noticed.