Neonatal Oxygen Exposure in Rats Leads to Cardiovascular and Renal Alterations in Adulthood

Abstract

Abstract-Long-term vascular and renal consequences of neonatal oxidative injury are unknown. Using a rat model, we sought to investigate whether vascular function and blood pressure are altered in adult rats exposed to hyperoxic conditions as neonates. We also questioned whether neonatal O 2 injury causes long-term renal damage, important in the pathogenesis of hypertension. Sprague-Dawley pups were kept with their mother in 80% O 2 or room air from days 3 to 10 postnatal, and blood pressure was measured (tail cuff) from weeks 7 to 15. Rats were euthanized, and vascular reactivity (ex vivo carotid rings), oxidative stress (lucigenin chemiluminescence and dihydroethidium fluorescence), microvascular density (tibialis anterior muscle), and nephron count were studied. In male and female rats exposed to O 2 as newborns, systolic and diastolic blood pressures were increased (by an average of 15 mm Hg); ex vivo, maximal vasoconstriction (both genders) and sensitivity (males only) specific to angiotensin II were increased; endotheliumdependant vasodilatation to carbachol but not to NO-donor sodium nitroprussiate was impaired; superoxide dismutase analogue prevented vascular dysfunction to angiotensin II and carbachol; vascular superoxide production was higher; and capillary density (by 30%) and number of nephrons per kidney (by 25%) were decreased. These data suggest that neonatal hyperoxia leads in the adult rat to increased blood pressure, vascular dysfunction, microvascular rarefaction, and reduced nephron number in both genders. Our findings support the hypothesis of developmental programming of adult cardiovascular and renal diseases and provide new insights into the potential role of oxidative stress in this process. Key Words: hypertension Ⅲ vascular dysfunction Ⅲ developmental origin of adult onset disease Ⅲ oxygen Ⅲ angiotensin Ⅲ microvascular rarefaction Ⅲ nephron number P remature babies, representing Ϸ8% of all births, have decreased antioxidant defenses and are exposed on birth to high oxygen (O 2 ) concentration relative to the intrauterine milieu. 1,2 This results in high O 2 -derived free radicals. Evidence in humans and animal studies indicate that premature newborns are more susceptible to oxidative tissue damage, leading to pathologies such as retinopathy of prematurity and bronchopulmonary dysplasia. 3,4 However, the long-term vascular and blood pressure consequences of neonatal hyperoxic injury are unknown.It is becoming increasingly evident that conditions early in life can influence adult diseases; however, the mechanisms are incompletely understood. 5,6 Recent data suggest that perinatal oxidative stress may be the initiating trigger in long-term programming of cardiovascular function. In a previous study, we found that cellular antioxidant glutathione is decreased in the fetus of dams fed a low-protein (LP) diet during gestation. In that model, administration of the peroxidation inhibitor lazaroid to the pregnant dam prevented elevated blood pressure, vascular dysfunction, and microvascular rar...

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