2026-09-21T04:06:52Zhttps://wakespace.lib.wfu.edu/server/oai/request

oai:null:10339/593132026-09-18T13:27:37Zcom_10339_14934col_10339_38132

Kaiser, Christopher 2016-05-21T08:35:51Z 2018-05-20T08:30:12Z 2016 https://wakespace.lib.wfu.edu/handle/10339/59313 Preterm (PT) birth is defined as being born at less than 37 weeks gestation. Although the incidence of PT birth has decreased in recent years, as of 2014, 9.6% infants were born PT.1 Additionally, 1.4% of all live births in the U.S. are very low birth weight (VLBW < 1500g).2 PT infants are at a higher risk of infant death compared to healthy term born peers, with PT birth accounting for 1/3 of infant mortality.1,3 Survivors of PT birth face a number of short and long-term consequences including respiratory, neurodevelopmental, and cardiovascular complications, in addition to increased mortality.3 Adults born PT have been shown to have higher incidence of hypertension (HTN) and mortality due to cardiovascular disease (CVD) risk when compared with healthy term born peers.4,5 This relationship may be partly attributable to the fetal origins of adult disease (FOAD) hypothesis, which proposes that adverse events during key developmental windows alter organ system structure and function that promotes survival in the short-term, but may be detrimental in the long-term, leading to higher risk for developing chronic diseases such as hypertension, cardiovascular disease, and diabetes later in life.6,7 The kidney is one organ system that may be affected, and is especially important in terms of blood pressure (BP) regulation. Nephrogenesis begins by 9 weeks gestation, however kidney formation is not complete until around 32-36 weeks.8 Both animal and human studies indicate that PT birth is associated with reduced nephron number, which may lead to hypertension.8,9 There is growing 2 evidence that the renin angiotensin system (RAS), another key component of BP control, may also be affected by both PT birth, as well as kidney development.10–13 In RAS, Angiotensin II (Ang II) acts as a vasoconstrictor, ultimately raising BP, whereas Angiotensin 1-7 (Ang 1-7) acts as a vasodilator and lowers BP.14,15 High levels of Ang II is associated with higher blood pressure, and chronic diseases such as CVD and diabetes; on the other hand Ang 1-7 has been shown to have cardio protective effects.16 When compared with healthy term born peers, adults born PT and/or VLBW have been shown to have elevated levels of plasma Ang II, in addition to elevated levels of angiotensin converting enzyme (ACE; the enzyme that converts ANGI to AngII), ultimately implicating RAS as having a role in developing HTN within this population.10,11,13 Preterm birth has also been associated with reduced cardiorespiratory fitness as well as participation in physical activity (PA).17,18 It is well established that individuals who participate in more PA, or have higher aerobic fitness, are at lower risk of developing hypertension and other cardio metabolic diseases.19–22 Consequently, lower PA and aerobic fitness may put this predisposed population at even greater risk for developing HTN and other diseases.17,23–25 Little research has been done examining the influence of PA and fitness on RAS, with no studies examining these relationships in PT populations. A metaanalysis examining the effects of exercise on RAS found lower plasma renin activity post aerobic training.26 Additionally, one animal model demonstrated that rats exposed to a 16 week PA program had lower levels of ACE, Ang II, and BP when compared to rats that did not participate in PA.27 If this same relationship exists in 3 humans, then adults born PT who participate in PA and have higher cardio respiratory fitness (CRF) may have more favorable RAS, and subsequently lower BP and HTN risk. In summary, there is some evidence that being born PT and/or VLBW is associated with higher ACE and Ang II levels10,11,13 which in turn has been associated with hypertension and other cardiometabolic diseases. There is evidence that PT/VLBW persons have lower PA and fitness, which is also associated with higher BP and other chronic diseases.19,20,23,24 Lastly, there is evidence in animal models that PA may decrease the ACE/Ang II levels.27 However, to date no study has examined the influence of PT birth on RAS and the role that fitness and PA may have on its association. Therefore, the aims of this study are to examine RAS in PT/VLBW adolescents compared to their term-born peers, and the potential mediating influence of PA and fitness on the association between PT birth and RAS. Understanding this relationship may help to determine preventative or therapeutic strategies for this at risk population. en Wake Forest University AEROBIC FITNESS AND THE RENIN ANGIOTENSIN SYSTEM IN ADOLESCENTS BORN PRETERM WITH VERY LOW BIRTH WEIGHT Thesis Nixon, Patricia Washburn, Lisa Health and Exercise Science 2018-05-20 open.access