Ontogeny of cardiovascular control in amphibians

SYNOPSIS. Cardiovascular variables in developing amphibians are affected by both allometry and organogenesis. Blood pressure, cardiac output, and stroke volume increase during development, whereas peripheral resistance decreases. Invariably, resting heart rate changes as development proceeds from embryo through larva to adult. The pattern of change, however, varies between species and does not even correlate with family. The mechanisms underlying these varying patterns of developmental changes in heart rate of anuran amphibians larvae awaits complete description. Cardiovascular vari-ables in adult vertebrates are influenced by nerves and hormones as well as intrinsic factors. However, information on the development of cardiovascu-lar control systems is scarce, but receptor sensitivity apparently develops be-fore functional innervation becomes apparent. The amphibian heart responds to acetylcholine and adrenaline several stages before functional innervation becomes evident, and in some species the cholinergic and adrenergic sensi-tivity of the cardiac pacemaker changes with development. As in mammals, acute hypoxia results in different cardiovascular responses depending on the developmental stage of the animal. The different responses reflect the rela-tive maturity of neurohormonal mechanisms operating within the cardiovas-cular system