Cardiovascular and renal effects of ANG II and NO in the newborn: roles of AT1Rs and /or AT2Rs

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The vasoactive factors angiotensin II (ANG II) and nitric oxide (NO), and the balance between them play a major role in regulating cardiovascular and electrolyte homeostasis. During the perinatal period, both factors are elevated, yet their physiological roles have not been clearly defined. Furthermore, the temporal and spatial expression of the receptors for ANG II (AT1Rs and AT2Rs) is developmentally regulated, although their physiological roles are also unknown. The present study aimed to elucidate for the first time, the physiological effects of ANG II on the kidney during postnatal maturation, as well as the potential role of the ATRs in initiating these physiological effects. In addition, this study investigated for the first time the interaction between ANG II and NO in regulating cardiovascular and renal function during the period of adaptation of the newborn to life after birth. Two study protocols were carried out in conscious lambs at two stages of postnatal maturation - one and six weeks. The first protocol evaluated (a) the individual functions of ATRs and (b) any possible interaction between them in mediating haemodynamic and renal physiological responses of ANG II. The second protocol investigated the roles of ATRs in modulating physiological roles of endogenoulsy produced NO during development. Results from these experiments show for the first time, that there does not appear to be any interaction between AT1Rs and AT2Rs in mediating haemodynamic effects of endogenous ANG II early in life. In contrast, the renal effects of ANG II are mediated through AT1Rs in an age-dependent manner, whereas AT2Rs buffer these effects. My research also shows for the first time, that ANG II modulates the effects of NO on renal haemodynamics and function but not systemic haemodynamics in an age-dependent manner through activation of AT1Rs and AT2Rs. Furthermore, it appears that AT2Rs interact with AT1Rs in mediating the renal effects of NO in developing newborn animals. This is the first description of renal effects of ANG II and a new and important interaction between ANG II and NO under physiological conditions early in life.
Vinturache, A. E. (2012). Cardiovascular and renal effects of ANG II and NO in the newborn: roles of AT1Rs and /or AT2Rs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/25214