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Development of hemodynamic regulation in the African clawed toad Xenopus laevis
Abstract
Cardiovascular variables were measured in larvae of Xenopus laevis from hatching (2 mg) to the end of metamorphosis (1213 mg). Blood pressures were measured by a servo-null micropressure system. Stroke volumes (SV) were measured by video taping cardiac cycles through a dissecting microscope. Mean truncus pressure increases continuously with increasing body mass, indicating a continuous increase in contraction force of the heart. Peripheral vascular resistance decreases greatly with increasing body mass, suggesting that an increase in total cross-sectional area of whole vasculature is predominant. As a result, SV, cardiac output, and cardiac work increase continuously with increasing body mass during larval development. Heart rate (f$\sb{\rm H})$ increases initially, then decreases (at stage 48) for the rest of larval development. However, changes in f$\sb{\rm H}$ are explained very little by body mass. Except for the change in f$\sb{\rm H},$ patterns of hemodynamic development in larval Xenopus laevis are similar to those in other vertebrate embryos/larvae examined. This suggests the presence of a general pattern for development of cardiovascular function in vertebrates. At stage 41 (2nd day after hatching), f$\sb{\rm H}$ in larval Xenopus laevis increases during environmental hypoxia or presence of MS-222. The mechanism for increases of f$\sb{\rm H}$ in stage 41 is probably hormonal, because the heart is not innervated at this stage. Heart rates during hypoxia also increase in larvae of stage 46-47 but remain unchanged in larvae of stage 49. At stage 48 (5 days after hatching), f$\sb{\rm H}$ increases with injection of atropine, suggesting the presence of tonic vagal inhibition of the heart at this stage. This vagal tone occurs soon after the cholinergic nerves occur in heart. Neural regulation of the heart in larval Xenopus laevis begins in the second week of the two month long larval development, while that in chick embryos occurs in the later half of the 21-day incubation period.
Subject Area
Zoology|Physiology
Recommended Citation
Hou, Ping-Chun Lucy, "Development of hemodynamic regulation in the African clawed toad Xenopus laevis" (1992). Doctoral Dissertations Available from Proquest. AAI9219446.
https://scholarworks.umass.edu/dissertations/AAI9219446