ANALYSIS OF RESPIRATORY WATER - A NEW METHOD FOR EVALUATION OF MYOCARDIAL ENERGY-METABOLISM

Aerobic ATP synthesis via oxidative phosphorylation causes a proportio nal production of respiratory water. Thus the amount of respiratory wa ter produced at a given time should be a reliable measure of the curre nt ATP demand of the mammalian myocardium. Respiratory water from isol ated rabbit hearts was labeled by using the stable oxygen isotope O-18 . The hearts were perfused according to the method of Langendorff (O. Langendorff. Pfluegers Arch. 61: 291-332, 1895) with O-18(2)-equilibra ted Krebs-Henseleit solution. Control hearts were exclusively perfused with carbogen-equilibrated Krebs-Henseleit solution. Myocardial tissu e was then lyophilized; the extracted water and samples from the coron ary venous effluent were converted to CO2 by using the guanidine hydro chloride technique. The delta(18)O values within the CO2 samples were determined by mass spectrometry and related to the standard mean ocean water (SMOW) scale. Compared with control hearts, the O-18-labeled he arts exhibited a significant increase of delta(18)O values from tissue water (-47.50 +/- 0.64 vs. -40.35 +/- 2.05 parts per thousand SMOW; P < 0.05). The values were also significantly increased in the coronary venous effluent after a perfusion time of only 50 s (-47.50 +/- 0.64 vs. -43.66 +/- 0.91 parts per thousand SMOW; P < 0.05). Thus this firs t adaptation of the guanidine hydrochloride technique on microliter sa mples of myocardial tissue water and coronary venous effluent demonstr ates that this method can be used to evaluate both respiratory activit y and the kinetics of cardiac metabolic processes.