Identification of Site of Morphine Action in Pregnant Wistar Rat Placenta Tissue: A C14-Morphine Study

In previous studies it has been emphasized that the site of morphine action may be either in the embryo or the placenta. In the present study, we attempt to identify the site of morphine action on the fetal section of Wistar rat placenta by using C14-morphine. In this study (experimental), female Wistar rats (weights: 170-200 g) were mated with male rats and their coupling times recorded. Experimental groups received daily doses of 0.05 mg/ml of C14-morphine in their drinking water. On the 9th and14th embryonic days, the pregnant rats were anesthetized and the placenta and uterus surgically removed. Placentas were fixed in 10% formalin for two weeks, then processed, sectioned in 5 μm and 25 μm thicknesses, and fixed on glass slides for further evaluation. The 25 μm sections were delivered to black and white film for three days. Films were processed and evaluated with a digital inverse microscope for possible radiological impression. The 5 μm sections were processed for hematoxylin and eosin (H&E) staining, and evaluated by light microscope and MOTIC software. Our results indicated that the site of action of C14-morphine was possibly located on the blood plexus of the fetal portion of the placenta. In addition, oral morphine consumption was shown to inhibit fetal and maternal placental development in the experimental groups. We conclude that morphine’s effectiveness on the reduction of embryo growth and development may be via its effects on the blood plexus of the fetal section of the placenta.