Maternal low-protein diet programs cardiac β-adrenergic response and signaling in 3-mo-old male offspring

Abstract
Low birth weight in humans is associated with an increased risk of cardiovascular disease. Humans with heart failure have a reduced β-adrenergic response. The aim of this study was to investigate the hemodynamic response to the β-adrenergic agonist isoproterenol and to identify molecular deficiencies that may be predictive of cardiac failure in a low-birth weight rodent model that develops insulin resistance and type 2 diabetes in adulthood. Wistar rats were fed a control or a low-protein (LP) diet throughout pregnancy and lactation. The resting heart rate and blood pressure of the 3-mo-old male offspring of these dams, termed “control” and “LP” groups, respectively, and their responses to isoproterenol (ISO) infusion were monitored by radiotelemetry. The protein expression of β-adrenergic signaling components was also measured by Western blot analysis. Basal heart rate was increased in LP offspring ( P < 0.04), although mean arterial pressure was comparable with controls. Chronotropic effects of ISO were blunted in LP offspring with significant delays to maximal response ( P = 0.01), a shorter duration of response ( P = 0.03), and a delayed return to baseline ( P = 0.01) at the lower dose (0.1 μg·kg−1·min−1). At the higher dose (1.0 μg·kg−1·min−1ISO), inotropic response was blunted ( P = 0.03) but quicker ( P = 0.001). In heart tissue of LP offspring, β1-adrenergic receptor expression was reduced ( P < 0.03). β1-Adrenergic receptor kinase and both stimulatory and inhibitory G protein levels remained unchanged, whereas β-arrestin levels were higher ( P < 0.03). Finally, insulin receptor-β expression was reduced in LP offspring ( P < 0.012). LP offspring have reduced β-adrenergic responsiveness and attenuated adrenergic and insulin signaling, suggesting that intrauterine undernutrition alters heart failure risk.
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