Developmental programming of cardiovascular dysfunction by prenatal hypoxia and oxidative stress

Abstract

Fetal hypoxia is a common complication of pregnancy. It has been shown to programme cardiac and endothelial dysfunction in the offspring in adult life. However, the mechanisms via which this occurs remain elusive, precluding the identification of potential therapy. Using an integrative approach at the isolated organ, cellular and molecular levels, we tested the hypothesis that oxidative stress in the fetal heart and vasculature underlies the molecular basis via which prenatal hypoxia programmes cardiovascular dysfunction in later life. In a longitudinal study, the effects of maternal treatment of hypoxic (13% O(2)) pregnancy with an antioxidant on the cardiovascular system of the offspring at the end of gestation and at adulthood were studied. On day 6 of pregnancy, rats (n = 20 per group) were exposed to normoxia or hypoxia ± vitamin C. At gestational day 20, tissues were collected from 1 male fetus per litter per group (n = 10). The remaining 10 litters per group were allowed to deliver. At 4 months, tissues from 1 male adult offspring per litter per group were either perfusion fixed, frozen, or dissected for isolated organ preparations. In the fetus, hypoxic pregnancy promoted aortic thickening with enhanced nitrotyrosine staining and an increase in cardiac HSP70 expression. By adulthood, offspring of hypoxic pregnancy had markedly impaired NO-dependent relaxation in femoral resistance arteries, and increased myocardial contractility with sympathetic dominance. Maternal vitamin C prevented these effects in fetal and adult offspring of hypoxic pregnancy. The data offer insight to mechanism and thereby possible targets for intervention against developmental origins of cardiac and peripheral vascular dysfunction in offspring of risky pregnancy.

Figure 1. Fetal aorta and heart.

Photomicrographs of individual examples of sections of the fetal aorta are shown in a. Bar scale is 100 µm. Values are mean±S.E.M. of the wall to lumen area ratio b; the density of nitrotyrosine staining in the aortic wall c, and the protein expression of HSP70 in the fetal heart d. Groups are: Normoxia, n = 8 (N,□), Hypoxia, n = 8 (H,▪), Hypoxia+Vitamin C, n = 8 (HC, red histogram) and Normoxic+Vitamin C, n = 8 (NC, blue histogram). Significant (P<0.05) differences are: * vs. all, † vs. H, One-Way ANOVA with Tukey Test.

Figure 2. Femoral artery vasodilator function in adulthood.

Values are mean±S.E.M. for the concentration-response curve (maximal response, %Rmax, and sensitivity, pD2) to sodium nitroprusside (SNP) a and to methacholine (MetCh) b, and for the nitric oxide (NO) dependent and independent components (area under the curve, AUC) of the endothelial dependent vasorelaxation c in femoral resistance arteries isolated from 4 month adult offspring. Concentration-response curves were analysed using an agonist-response best-fit line. The maximal relaxant response (%Rmax) was expressed as percentage of the contraction induced by PE and the vascular sensitivity was expressed as pD2 (-logEC50). The contribution of NO-dependent mechanisms to the relaxation induced by MetCh was calculated by subtracting the area under the curve (AUC) for MetCh – the AUC for MetCh + LNAME. The contribution of NO-independent mechanisms was calculated by the AUC for MetCh + LNAME . Groups are: Normoxia, n = 8 (N, white symbols), Hypoxia, n = 8 (H, black symbols), Hypoxia+Vitamin C, n = 6 (HC, red symbols) and Normoxic+Vitamin C, n = 8 (NC, blue symbols). Significant (P<0.05) differences are: * vs. N, † vs. H, One-Way ANOVA with Tukey Test.

Figure 3. Cardiac function in adulthood.

Values are mean±S.E.M. for the dP/dt max a, the heart rate-pressure product (RPP) b; and the heart rate responses to 10–6 M Carbachol c and to 10–7 M Isoprenaline d. Groups are: Normoxia, n = 6 (N,□), Hypoxia, n = 6 (H, ▪), Hypoxia+Vitamin C, n = 7 (HC, red histogram) and Normoxic+Vitamin C, n = 7 (NC, blue histogram). Significant (P<0.05) differences are: * vs. all, One-Way ANOVA with Tukey Test.