AUTORADIOGRAPHY REVEALS REGIONAL METABOLIC DIFFERENCES IN THE ENDOMETRIUM OF PREGNANT AND NONPREGNANT MICE

The rodent endometrium undergoes remarkable modifications during pregn ancy, resulting from a redifferentiation of its fibroblasts. During th is modification (decidualization), the fibroblasts transform into larg e, polyhedral cells that establish intercellular junctions. Decidualiz ation proceeds from the subepithelial stroma towards the deep stroma s ituated next to the myometrium and creates regions composed of cells i n different stages of differentiation. We studied by autoradiography w hether cells of these different regions have different levels of macro molecular synthesis. Radioactive amino acids or radioactive sulfate we re administered to mice during estrus or on different days of pregnanc y. The animals were killed 30 min after injection of the precursors an d the uteri were processed for light microscope autoradiography. Silve r grains were counted over cells of different regions of the endometri um and are reported as the number of silver grains per area. Higher le vels of incorporation of amino acids were found in pregnant animals as compared to animals in estrus. In pregnant animals, the region of dec idual cells or the region of fibroblasts transforming into decidual ce lls showed the highest levels of synthesis. Radioactive sulfate incorp oration, on the other hand, was generally higher in nonpregnant animal s. Animals without decidual cell transformation (nonpregnant and 4th d ay of pregnancy) showed a differential incorporation by subepithelial and deep stroma fibroblasts. This study shows that regional difference s in synthetic activity exist in cells that are in different stages of transformation into decidual cells as well as in different regions of the endometrium of nonpregnant mice.