AJP - Heart and Circulatory Physiology, Vol 253, Issue 6 1441-H1448, Copyright © 1987 by American Physiological Society
Influence of acidosis on inotropic effect of catecholamines in newborn rabbit hearts
T. Nakanishi, H. Okuda, K. Kamata, M. Seguchi, M. Nakazawa and A. Takao
Heart Institute of Japan, Tokyo Women's Medical College.
The influence of acidosis on the inotropic effect of isoproterenol was
studied in the isolated arterially perfused heart of the newborn rabbits.
Baseline mechanical function during acidosis (pH 6.8) was not different
from control (pH 7.4). However, the inotropic effect of isoproterenol was
significantly suppressed in the acidotic muscles. The increment of
myocardial adenosine 3',5'-cyclic monophosphate (cAMP) content during
isoproterenol infusion was also reduced in acidosis. Inotropic effects of
Ca and dibutyryl cAMP in the acidotic muscles were not significantly
different from those in the control muscles. beta-Receptor number and
affinity in the respiratory acidotic muscle was similar to those in the
control muscle. Effects of pH on myocardial beta-receptor and adenylate
cyclase activity were further determined in the membrane fraction by
changing the pH of the reaction medium from 7.4 (control) to 6.8 or 6.0.
beta-Receptor numbers were significantly decreased at pH 6.0 but not at pH
6.8. Adenylate cyclase activity was depressed at pH 6.8 and 6.0. These data
suggest that the inotropic effect of isoproterenol is diminished in the
acidotic muscle. This may be due to the decreased activation of cAMP
production, which in turn most likely results from depressed adenylate
cyclase activity.
