Pregnancy reverses hypertensive remodeling of cerebral arteries.

Previous studies have shown that pregnancy prevents hypertensive remodeling of cerebral arteries. In the present study, we sought to determine whether pregnancy could reverse preexisting remodeling. Nonpregnant virgin Sprague-Dawley rats were treated with the NO synthase inhibitor nitro-l-arginine (0.5 g/L in drinking water) for 2 weeks before mating, after which treatment continued until late gestation for a total of 5 weeks. Pregnant animals with preexisting hypertension (n=6) were compared with nonpregnant animals that were treated with nitro-l-arginine for either 2 (n=8) or 5 (n=9) weeks and compared with nontreated controls (n=8). Blood pressure, passive and active diameters, wall thickness, media thickness, and passive distensibility of cerebral arteries were compared between groups. Treatment with nitro-l-arginine caused a significant increase in mean arterial pressure in all of the groups compared with controls that was sustained for the entire study: 103+/-3 versus 137+/-2, 141+/-4, and 140+/-7 mm Hg (P<0.01). Both 2 and 5 weeks of hypertension caused inward eutrophic remodeling in nonpregnant animals, characterized by decreased inner and outer lumen diameters and no change in media thickness. Pregnancy reversed this remodeling, because late-pregnant animals with preexisting hypertension had inner and outer diameters similar to controls. Passive distensibility was significantly less, and active myogenic tone increased in all of the hypertensive animals, independent of pregnancy. These results demonstrate that pregnancy reverses preexisting hypertensive remodeling of cerebral arteries without a decrease in blood pressure. This reversal of protective remodeling during hypertension in pregnancy may be detrimental by lowering the upper limit of autoregulation, whereas blood pressure remains elevated.