The effect of pregnancy on the elastic membranes of mesometrial arteries in the guinea pig

Mesometrial arteries were obtained at various stages from adult virgin and primiparous guinea pigs beginning at pregnancy and ending at 40 days post‐partum. The tissues were processed routinely and then stained with hematoxylin and eosin, and various elastic tissue stains. Picro‐indigo‐carmine and Van Gieson were used as counterstains. It was found that during the early stages of pregnancy the subendothelial cells of mesometrial arteries began to proliferate and the internal elastic membrane showed signs of fragmentation. By term the subendothelial cells formed a several layer thick cushion and the elastic fibers were virtually absent. About 22 days post‐partum the subendothelial cells had disappeared and a new internal elastic membrane had formed. These changes are found mainly in the placental mesometrial arteries and to a lesser degree in the peripheral ones. Guinea pigs with unilateral pregnancies exhibited the above changes only on the side of the pregnant horn. It is suggested that the above changes are due to pregnancy and that local hormones elaborated by the placenta may be largely responsible for the alterations in the mesometrial arteries during pregnancy.