AJP - Heart and Circulatory Physiology, Vol 246, Issue 2 213-H221, Copyright © 1984 by American Physiological Society
Ouabain effect on myocardial mechanical function and sodium pump in the fetus
T. Nakanishi, T. Shimizu, S. Uemura and J. M. Jarmakani
Effects of ouabain (0.75, 1, 1.5, 2.5 or 5 X 10(-6) M) on the mechanical
function and sodium pump were studied in the isolated arterially perfused
fetal and newborn rabbit heart. Measurement of myocardial 86Rb+ active
uptake was used as a marker of the sodium pump activity. The inotropic
effect of ouabain in the fetus was not significantly different from that in
the newborn; 2.5 X 10(-6) M ouabain caused mechanical toxicity (decrease in
+dT/dtmax and increase in resting tension) in the fetus but not in the
newborn. After ouabain infusion, both the inhibition of Rb+ uptake and the
significant decrease in tissue potassium content were similar in the fetus
and the newborn. In the fetal muscle perfused with low calcium (0.5 mM)
solution, mechanical toxicity of ouabain was significantly less than in the
control (1.5 mM Ca2+) solutions. High extracellular calcium (30 mM) per se
caused mechanical toxicity in the fetus but not in the newborn. These data
indicate that, in the isolated arterially perfused heart preparation,
mechanical toxicity in the fetus is observed at lower ouabain
concentrations than in the newborn. This difference in mechanical toxicity
may not be explained by the age-related difference in sodium pump activity.
The greater calcium toxicity in the fetus may be the reason for the
increased ouabain toxicity in this age group.
