AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 5 997-1004, Copyright © 1996 by American Physiological Society
Cardiac output in Xenopus laevis tadpoles during development and in response to an adenosine agonist
Y. Y. Tang and C. M. Rovainen
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
We test the hypothesis that the heart and arteries enlarge with increased
cardiac output (CO) during development and volume overload. Transparent
albino tadpoles of Xenopus laevis at stages 43-50 were anesthetized in
0.3-0.5 mM benzocaine. Areas and radii [maximum and minimum radius (Rmax
and Rmin, respectively)] of the ventricle were measured in digitized video
frames during the cardiac cycle. Stroke volume (SV) and CO were calculated
from Rmax and Rmin. Maximal velocities of 3.4-microns fluorescent beads
were measured in the aortic arches. Arterial pressure was estimated by the
Landis method. During normal development, the radii of the ventricle and
aortic arch diameters increased with lengths of tadpoles, and SV (0.7
microliters/g) and CO (70 microliters.g-1.min-1) with wet weights. Volume
overload was induced by a vasodilatory adenosine agonist
5'-N-ethylcarboxamidoadenosine (NECA) in the aquarium water. Acute (0.5-4
h) NECA significantly increased Rmax and heart rate. Chronic (> 1 wk)
NECA significantly increased both Rmax and Rmin. SV and CO increased more
than two times, blood pressures decreased, and specific vascular
conductances increased more than five times. It is concluded that NECA
increases CO in Xenopus tadpoles through a combination of increased filling
and accelerated growth.
