Remodelling of guinea-pig aorta during pregnancy: selective alteration of endothelial cells

It is known that aortic blood flow is increased during pregnancy, which may be due to a pregnancy-associated decrease in aorta sensitivity to vasoconstrictors on one side, and increased response to vasodilators on the other. Recent studies have shown that alteration of blood flow or pressure could remodel some arteries over a short time frame. However, the possibility of remodelling of aorta during pregnancy has not yet been examined. Therefore, the aim of the present study was to assess the morphometric and stereological characteristics of guinea-pig aorta during different stages of pregnancy (non-pregnant, early-pregnant, mid-pregnant, late-pregnant, n = 8-10 for each group). The cross-sectional areas of different aortic layers and of endothelial cells were measured using both light and electron microscopy. The values of external and internal diameters, wall thickness, total cross-sectional area and cross-sectional area of media and adventitia were not significantly different, regardless of the stage of pregnancy. In contrast, the cross-sectional area of intima significantly and progressively decreased during pregnancy (non-pregnant: 61 +/- 5 x 10(4) microm2, late-pregnant: 38 +/- 3 microm2, P < 0.01). The volume:surface density ratio of intima also significantly and progressively decreased during pregnancy (non-pregnant: 5.31 +/- 0.51, late-pregnant: 4.38 +/- 0.42, P < 0.01). Electron microscopy revealed that the cross-sectional area of endothelial cells was significantly decreased during different stages of pregnancy (non-pregnant: 56.8 +/- 6.2 microm2, late-pregnant: 28.9 +/- 3.8 microm2, P < 0.01). It is concluded that during pregnancy there is selective thinning of intimal layer of guinea-pig aorta, which probably reflects hypotrophy of aortic endothelial cells.