Structural changes in the uterine artery of the domestic pig (Sus scrofa domesticus) in the first trimester of pregnancy

Background: Adaptation of the uterine artery in pregnancy involves changes in anatomy that include widening of the lumen, medial thickening, elastic lamina degradation, and smooth muscle cell hypertrophy. Early remodeling of the uterine vascular system is needed to maintain pregnancy and ensure desired pregnancy outcome. The trigger mechanisms for uterine artery remodeling are uncertain. Also unclear are the regional variations in the uterine artery in the first trimester of pregnancy. Methods: 10 domestic pigs (Sus scrofa) 5 in the first trimester of pregnancy and 5 non gravid were sacrificed to examine the structure of the uterine artery. The specimens were prepared for paraffin wax embedding and stained with Masson’s Trichrome, Weigert’s Resorcin-Fuschscin counterstained with Van Gieson stain and Hematoxylin and Eosin. Slides were examined with a light microscope at x40, x100, and X400 magnification. Observations made were recorded and photomicrographs taken. Results: The Uterine artery of the domestic pig in the first trimester showed marked reduction in the thickness of the tunica intima, a prominent internal elastic lamina and elastic fibres. The tunica media had hypertrophied vascular smooth muscle with zonation of the media into inner circular and outer longitudinal smooth muscle layers in the proximal regions of the artery. There was also prominence of the Vasa vasorum in the adventitia of these uterine arteries that reduced distally along the artery. Conclusion: The proximal sections of the uterine artery shows unique physical- mechanical adaptation in the first trimester of pregnancy related to increased demand of blood to the feto-placental unit.