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      Prenatal hypoxia induces increased cardiac contractility on a background of decreased capillary density

      , 1 , 2

      BMC Cardiovascular Disorders

      BioMed Central

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          Abstract

          Background

          Chronic hypoxia in utero (CHU) is one of the most common insults to fetal development and may be associated with poor cardiac recovery from ischaemia-reperfusion injury, yet the effects on normal cardiac mechanical performance are poorly understood.

          Methods

          Pregnant female wistar rats were exposed to hypoxia (12% oxygen, balance nitrogen) for days 10–20 of pregnancy. Pups were born into normal room air and weaned normally. At 10 weeks of age, hearts were excised under anaesthesia and underwent retrograde 'Langendorff' perfusion. Mechanical performance was measured at constant filling pressure (100 cm H 2O) with intraventricular balloon. Left ventricular free wall was dissected away and capillary density estimated following alkaline phosphatase staining. Expression of SERCA2a and Nitric Oxide Synthases (NOS) proteins were estimated by immunoblotting.

          Results

          CHU significantly increased body mass (P < 0.001) compared with age-matched control rats but was without effect on relative cardiac mass. For incremental increases in left ventricular balloon volume, diastolic pressure was preserved. However, systolic pressure was significantly greater following CHU for balloon volume = 50 μl (P < 0.01) and up to 200 μl (P < 0.05). For higher balloon volumes systolic pressure was not significantly different from control. Developed pressures were correspondingly increased relative to controls for balloon volumes up to 250 μl (P < 0.05). Left ventricular free wall capillary density was significantly decreased in both epicardium (18%; P < 0.05) and endocardium (11%; P < 0.05) despite preserved coronary flow. Western blot analysis revealed no change to the expression of SERCA2a or nNOS but immuno-detectable eNOS protein was significantly decreased (P < 0.001) in cardiac tissue following chronic hypoxia in utero.

          Conclusion

          These data offer potential mechanisms for poor recovery following ischaemia, including decreased coronary flow reserve and impaired angiogenesis with subsequent detrimental effects of post-natal cardiac performance.

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          Most cited references 57

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          Hypoxia or nutrient restriction during pregnancy in rats leads to progressive cardiac remodeling and impairs postischemic recovery in adult male offspring.

          Intrauterine growth restriction (IUGR) increases the risk of developing adult-onset cardiovascular disease. We hypothesized that IUGR resulting from maternal hypoxia or nutrient restriction during late gestation will produce cardiac remodeling and impair cardiac recovery after ischemia/reperfusion (I/R) in adult male offspring aged 4 or 7 mo. Sprague-Dawley rats were randomized on day 15 of pregnancy to hypoxia (IUGR-H, 12% oxygen), nutrient restriction (IUGR-NR, 40% of control diet) or control (room air) groups. In 4-mo IUGR-H offspring, left ventricular wt/body wt ratio (LVW/BW) and right ventricular wt/BW ratio (RVW/BW) increased, in association with increased collagen I and III expression, beta and alpha myosin heavy chain (beta/alphaMHC) ratio, and decreased matrix metalloproteinase (MMP)-2 activity compared to the other groups. Left ventricular end diastolic pressure was higher in perfused hearts. Functional recovery after I/R was remarkably reduced (10+/-3%) compared to both control (39+/-5%) and IUGR-NR rats (32+/-4%). At 7 mo, both IUGR-H and IUGR-NR offspring had increased LVW/BW, collagen I and III, beta/alpha MHC ratio, and decreased cardiac recovery and MMP-2 activity compared to control. These findings suggest that hypoxia or undernutrition during development leads to pathological cardiac remodeling, diastolic dysfunction, and increased sensitivity to ischemic injury during adult life.
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            Developmental changes in contractility and sarcomeric proteins from the early embryonic to the adult stage in the mouse heart.

            Developmental changes in force-generating capacity and Ca2+ sensitivity of contraction in murine hearts were correlated with changes in myosin heavy chain (MHC) and troponin (Tn) isoform expression, using Triton-skinned fibres. The maximum Ca2+-activated isometric force normalized to the cross-sectional area (FCSA) increased mainly during embryogenesis and continued to increase at a slower rate until adulthood. During prenatal development, FCSA increased about 5-fold from embryonic day (E)10.5 to E19.5, while the amount of MHC normalized to the amount of total protein remained constant (from E13.5 to E19.5). This suggests that the development of structural organization of the myofilaments during the embryonic and the fetal period may play an important role for the improvement of force generation. There was an overall decrease of 0.5 pCa units in the Ca2+ sensitivity of force generation from E13.5 to the adult, of which the main decrease (0.3 pCa units) occurred within a short time interval, between E19.5 and 7 days after birth (7 days pn). Densitometric analysis of SDS-PAGE and Western blots revealed that the major switches between troponin T (TnT) isoforms occur before E16.5, whereas the transition points of slow skeletal troponin I (ssTnI) to cardiac TnI (cTnI) and of beta-MHC to alpha-MHC both occur around birth, in temporal correlation with the main decrease in Ca2+ sensitivity. To test whether the changes in Ca2+ sensitivity are solely based on Tn, the native Tn complex was replaced in fibres from E19.5 and adult hearts with fast skeletal Tn complex (fsTn) purified from rabbit skeletal muscle. The difference in pre-replacement values of pCa50 (-log([Ca2+] M-1)) required for half-maximum force development) between E19.5 (6.05 +/- 0.01) and adult fibres (5.64 +/- 0.04) was fully abolished after replacement with the exogenous skeletal Tn complex (pCa50 = 6.12 +/- 0.05 for both stages). This suggests that the major developmental changes in Ca2+ sensitivity of skinned murine myocardium originate primarily from the switch of ssTnI to cTnI.
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              Effect of maternal chronic hypoxic exposure during gestation on apoptosis in fetal rat heart.

              Chronic hypoxia during pregnancy is one of the most common insults to fetal development. We tested the hypothesis that maternal hypoxia induced apoptosis in the hearts of near-term fetal rats. Pregnant rats were divided into two groups, normoxic control and continuous hypoxic exposure (10.5% O2) from day 15 to 21 of gestation. Hearts were isolated from fetal rats of 21-day gestational age. Maternal hypoxia increased hypoxia-inducible factor-1alpha protein in fetal hearts. Chronic hypoxia significantly increased the percentage and size of binucleated myocytes and increased apoptotic cells from 1.4 +/- 0.14% to 2.7 +/- 0.3% in the fetal heart. In addition, the active cleaved form of caspase 3 was significantly increased in the hypoxic heart, which was associated with an increase in caspase 3 activity. There was a significant increase in Fas protein levels in the hypoxic heart. Chronic hypoxia did not change Bax protein levels but significantly decreased Bcl-2 proteins. In addition, chronic hypoxia significantly suppressed expression of heat shock protein 70. However, chronic hypoxia significantly increased expression of the anti-apoptotic protein 14-3-3, among other 14-3-3 isoforms. Chronic hypoxia differentially regulated beta-adrenoreceptor (beta-AR) subtypes with an increase in beta1-AR levels but no changes in beta2-AR. The results demonstrate that maternal hypoxia increases apoptosis in fetal rat heart, which may be mediated by an increase in Fas and a decrease in Bcl-2 proteins. Chronic hypoxia-mediated increase in beta1-AR and decrease in heat shock proteins may also play an important role in apoptosis in the fetal heart.
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                Author and article information

                Journal
                BMC Cardiovasc Disord
                BMC Cardiovascular Disorders
                BioMed Central
                1471-2261
                2009
                6 January 2009
                : 9
                : 1
                Affiliations
                [1 ]Department of Physiology, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham, B15 2TT, UK
                [2 ]Department of Vascular Studies, Northampton General Hospital, Northants, UK
                Article
                1471-2261-9-1
                10.1186/1471-2261-9-1
                2627821
                19126206
                Copyright © 2009 Hauton and Ousley; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Research Article

                Cardiovascular Medicine

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