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Most patients with hypertrophic cardiomyopathy and congenital heart diseases express the atrial essential myosin light chains (ALC-1) in their ventricles, replacing the ventricular essential light chains (VLC-1). VLC-1/ALC-1 isoform shift is correlated with increases in cardiac contractile parameters of a transgenic rat model overexpressing hALC-1 in the heart (TGR/hALC-1) compared to normal WKY rats. To investigate, whether the benefical effects of the hALC-1 on cardiac contractility could attenuate contractile failure of the overloaded heart, aortocaval shunt operations of 9-10 weeks old WKY and TGR/hALC-1 were performed. 5 weeks later, both animals groups were sacrificed for analysis of cardiac contraction and transgene expression. Control animals were operated but remained normal body and heart weights. The whole heart contractility parameters were evaluated using the Langendorff heart preparation. Shunt-operated TGR/hALC-1 and WKY rats developed comparable levels of cardiac hypertrophy which was associated with significant reduction of contractile parameters of the Langendorff hearts. However, the decline of cardiac contractility was less pronounced in shunt-operated TGR/hALC-1 compared to shunt-operated WKY. In fact, developed left ventricular pressure as well as maximal velocity of pressure development and relaxation were significantly higher in shunt-operated TGR/hALC-1 as compared to shunt-operated WKY. Expression of hALC-1 was 17 microg/mg whole SDS-protein in control (sham-operated) controls and declined significantly to 14 microg/mg whole SDS-protein in hypertrophied TGR/hALC-1. These results demonstrate that the expression of hALC-1 could have a beneficial effect on the overloaded hypertrophied heart.

Isolated, Langendorff-perfused, isovolumic preparations have been employed for many years to study cardiac function. In order to achieve isovolumic conditions a compliant balloon filled with a known volume of fluid is inserted into the left ventricle (LV). These preparations have a number of advantages over the in situ heart for the study of cardiac mechanics. First, hemodynamic and mechanical variables can be well controlled. The balloon allows accurate measurement and independent control of ventricular preload (end-diastolic volume), while isovolumic contraction results in a constant afterload. Heart rate can also be maintained constant by electronic pacing. Second, coronary perfusion pressure or flow, which independently influence both systolic and diastolic function, is independently maintained at desired levels. Moreover, left ventricular coronary flow and oxygen consumption and coronary vascular resistance can be estimated. Third, independent perfusion eliminates variable concentrations of circulating catecholamines and other substances, including anesthetic agents, which can influence cardiac performance. The fact that the heart is denervated also eliminates the effects of variations in direct autonomic nervous system stimulation.

The isolated heart, perfused with an electrolyte solution (usually a modified Krebs-Henseleit or Tyrode buffer), is a widely used experimental model for the study of cardiac performance. The hearts can be perfused in a retrograde (Langendorff heart) or antegrade way (working heart). However, the oxygen supply of these hearts is very unphysiological, with very high PO2 values but a limited oxygen concentration of the perfusion medium. Thire exists a great deal of disagreement about the adequacy of oxygenation of this preparation, and one may conclude that it is on the brink of hypoxia (see review by Kreuzer, in press; Figulla et al., 1983; Opie, 1984; Robiolio et al., 1989).

Previous studies from our laboratory utilized an isolated isovolumic Langendorff heart preparation to study myocardial metabolism and preservation of left ventricular function following global ischemia and reperfusion. The present study employed a similar preparation to assess the utilization of various glycolytic substrates by monitoring the level of left ventricular developed pressure. Twenty-one rabbit hearts were perfused with an oxygenated but substrate-free Krebs-Ringer-bicarbonate solution in order to deplete the hearts of endogeneous substrate stores. Following a brief period of anoxic, substrate-free perfusion, hearts were perfused with one of seven test substrates under anaerobic, then aerobic conditions. Under anaerobic conditions only perfusion of glucose resulted in a measurable increase in ventricular function which was still less than 20% of control. Under aerobic conditions, provision of glucose, pyruvate, or the combination of alpha-glycerol phosphate and pyruvate resulted in significant increases in contractile function which were 40-70% of control. These results obtained in normal hearts will provide a base line for future studies of the metabolism of postischemic hearts which may have altered cell membrane permeability and/or enzymatic activity.

The chromophoric substances which cause light absorption of optical spectra of the perfused Langendorff heart in the wavelength range of 500 to 650 nm are myoglobin and the cytochromes of the respiratory chain. We use a modified multicomponent analysis based on the two-flux theory of Kubelka and Munk (1931; Kubelka, 1948; 1954) to quantify the reflection spectra. Since the absorption spectra of the involved substances have overlapping absorption peaks and different forms, their concentration ratios are determined within different accuracy. The experiments show that the accuracy can be improved by the introduction of constraints, e.g. the reduction of the number of the basic absorption spectra. The constraints are worked out for the special measuring conditions.

Earlier experiments with the guinea pig brain had shown that at a temperature of 37° with a substrate-free macrodex solution, equilibrated with 95% O2 and 5% CO2 and with a large flow cytochrome aa3 (cyt aa3) was only about 60% oxidized (Schwickardi, 1968; Heinrich et al., 1981). Under similar conditions the heart muscle behaves differently: In the blood-free perfused Langendorff heart the cyt aa3 is about 95% oxidized (Figulla et al., 1979). Since in this case the perfusion medium was different, the question arises, whether the difference in the composition of the perfusion medium (for example the addition of substrate) influences the oxygen supply and can — at least in part — be responsible for the observed difference in the redox state of the respiratory chain. To have a better insight in the oxygen supply, in the following experiments, we combined the measurements of the redox states of the cytochromes with the measurements of Po2 histograms on the brain surface. The redox state of cytochrome aa3 serves as an indicator of the intracellular mitochondrial O2 supply, whereas the Po2 histogram indicates the Po2 distribution in the extracellular space. The measurements were performed with two different perfusion media and at two different temperatures.