AJP - Heart and Circulatory Physiology, Vol 243, Issue 2 289-H295, Copyright © 1982 by American Physiological Society
On-line calorimetry in the arterially perfused rabbit interventricular septum
J. E. Ponce-Hornos, N. V. Ricchiuti and G. A. Langer
A method has been developed to measure myocardial heat production
simultaneously with mechanical (developed tension, rate of contraction and
relaxation) and metabolic parameters in the arterially perfused
interventricular septum of the rabbit. The system allows control of rest
tension, frequency of contraction, temperature, and composition of the
perfusate. The technique is based on the differential measurement of the
heat flux from the muscle to the calorimetric bath. This technique is able
to resolve changes in heat production as small as 0.06 mW. The resting heat
production measured with the present calorimeter (1.62 +/- 0.1 mW/g wet
tissue) agrees with that obtained with thermopiles and with that calculated
from measurements of oxygen consumption. The heat per contraction (6.5 +/-
1.4 mJ/g wet tissue) also agreed with that measured with thermopiles in
rabbit papillary muscles. The heat production measured at 22 degrees C
under severe hypoxia can be fully explained by the addition of the expected
change of enthalpy due to the reaction 0.5 glucose-lactate, calculated on
the basis of the lactate measured in the perfusate, and the expected change
of enthalpy of oxygen consumption [assuming that all remaining O2 in
perfusate (0.09 vol%) is used for combustion of glucose]. These results
clearly demonstrated the feasibility of this method for the correlation of
changes in energy turnover, through the measurement of the heat production,
with mechanical and metabolic processes on-line in arterially perfused
septum.
