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  • Title: Angiotensin-(1-7) deficiency and baroreflex impairment precede the antenatal Betamethasone exposure-induced elevation in blood pressure.
    Author: Shaltout HA, Rose JC, Chappell MC, Diz DI.
    Journal: Hypertension; 2012 Feb; 59(2):453-8. PubMed ID: 22215705.
    Abstract:
    Betamethasone is administered to accelerate lung development and improve survival of premature infants but may be associated with hypertension later in life. In a sheep model of fetal programming resulting from exposure at day 80 of gestation to Betamethasone (Beta-exposed), adult sheep at 6 to 9 months or 1.8 years of age have elevated mean arterial pressure (MAP) and attenuated spontaneous baroreflex sensitivity (sBRS) for control of heart rate compared to age-matched controls associated with imbalances in angiotensin (Ang) II vs Ang-(1-7) tone. At 6 weeks of age, evoked BRS is already low in the Beta-exposed animals. In this study, we assessed the potential contribution of the renin-angiotensin system to the impaired sBRS. Female lambs (6 weeks old) with Beta exposure in utero had similar MAP to control lambs (78±2 vs 77±2 mm Hg, n=4-5 per group), but lower sBRS (8±1 vs 16±3 ms/mm Hg; P<0.05) and impaired heart rate variability. Peripheral AT1 receptor blockade using candesartan lowered MAP in both groups (≈10 mm Hg) and improved sBRS and heart rate variability in Beta-exposed lambs to a level similar to control. AT7 receptor blockade by infusion of D-ala Ang-(1-7) (700 ng/kg/min for 45 minutes) reduced sBRS 46%±10% in Beta-exposed vs in control lambs (P<0.15) and increased MAP in both groups (≈6±2 mm Hg). Our data reveal that Beta exposure impairs sBRS and heart rate variability at a time point preceding the elevation in MAP via mechanisms involving an imbalance in the Ang II/Ang-(1-7) ratio consistent with a progressive loss in Ang-(1-7) function.
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