Patterns of form and function in developing hearts: contributions from non-mammalian vertebrates.

Although most research on developmental cardiovascular physiology has focused on the bird embryo as a model for emulating developmental processes in mammals, there are increasingly compelling reasons to expand research to a variety of lower vertebrate systems. These reasons include circumventing inherent limitations of the avian embryo and identifying general vertebrate developmental patterns in the cardiovascular system. In this paper, we first review data from hemodynamic studies on amphibians and birds (and what little exists from fish and reptiles), to provide a background against which lower vertebrate development can be examined. We then describe non-mammalian, non-avian paradigms for studying developmental patterns of vertebrate hearts. Developmental spects of cardiovascular performance, especially heart rate, blood pressure and cardiac output and how they change with ontogeny, are described for several amphibians and a few reptiles, identifying, where possible, processes in common with birds and mammals. Finally, we indicate productive areas for future research with lower vertebrate cardiovascular systems, such as establishing "critical windows" for cardiovascular physiology during development, and determining the extent of developmental plasticity at the level of organ system physiology.