Influence of morphine during pregnancy on neuroendocrine regulation of pituitary hormone secretion

The effects of exposure to morphine during pregnancy on postnatal neuroendocrine systems were investigated. Rats received morphine sulphate or 0.9% (w/v) NaCl twice daily on days 5-12 of pregnancy. A dose of 5 mg morphine sulphate/kg was administered for the first three injections while 10 mg/kg was used for each of the remaining 13. This treatment regimen led to a significant delay in the onset of vaginal opening in the female offspring. Mothers treated with morphine sulphate showed a marked attenuation of their prolactin response to the suckling stimulus, although they still released significant amounts of the hormone. Both male and female offspring of the opiate-treated dams showed a major reduction in the sensitivity of their hypothalamic-pituitary axis to gonadal steroids at 15 days of age. No significant differences were found in the acute thyrotrophin response to single injection of morphine sulphate of prepuberal male and female pups of morphine- and saline-treated dams. These data show that exposure to opiates during critical periods of prenatal development lead to long-lasting alterations in the neuroendocrine control systems of the animal. These alterations may then have significant consequences on the physiological maturation and adult behaviour of the animal.