9307832 Burggren The cardiovascular system is the first organ system to operate in developing vertebrate embryos, and proper establishment of its transport functions is absolutely critical to the subsequent normal development of all tissues and organs. In spite of this important early role for the cardiovascular system, the development of its physiology remains very poorly understood for any vertebrate, including birds and mammals. Our initial findings on anuran amphibians (frogs) have been highly useful in advancing our understanding of studying the general properties of embryonic circulations. Consequently, support has been requested to expand our investigations of the development of central arterial blood pressure and flow generation and its regulation in embryos and larvae of the frog Xenopus laevis, which has become one of the major vertebrate models in development biology. The major objectives of this proposal are to: 1) determine the development of flow and pressure generation in the early embryonic heart, and 2) to determine how external and internal influences that lead to low tissue oxygenation and changes in blood transport demands affect both the short-term and long-term performance of the cardiovascular system in embryos and beyond to the adult. Measurement will include recordings of the heart rate heart output, blood pressure, peripheral resistance and heart work. The experimental design will encompass rearing populations of developing embryos under conditions that include short-term and long-term exposure to low oxygen levels, and subsequently assessing their physiological performance to determine when in development they are most vulnerable environmental disturbance. Our studies on physiological development and how environmental conditions impact upon it will have very broad applicability to both vertebrate physiology and developmental biology, particularly in the almost complete absence of similar published data on eit her bird or mammal embryos. ***
