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SUMMARY Microanalytical techniques have been developed for the quantitative determination of actomyosin and collagen from 20 to 30-mg (wet mass) samples of myocardium. Actomyosin is the major contractile protein complex and is, therefore, an index of functional muscle; collagen is the major protein of connective and scar tissue and is, therefore, an index of fibrosis. These proteins were determined in six myocardial samples from each of four normal, four ischemic, and three hypertrophied human hearts. As determined by electrophoresis in a denaturing medium, the concentration of actomyosin in normal myocardium is 69 /tg/mg wet tissue; the concentration in ischemic myocardium is not significantly different from normal, but is approximately 45% higher than normal in hearts with left ventricular hypertrophy. These observations indicate that hypertrophy is not simply an increase in total heart mass but, rather, involves an increase in actomyosin concentration in myocardial tissue as well. Collagen is determined from amino acid analysis of whole tissue for 4-hydroxyproline, an amino acid characteristic of this protein; the concentration of collagen in normal (6.1 /ig/mg wet tissue) myocardium are not significantly different from those in hypertrophied myocardium. In focal regions of ischemic hearts, however, collagen is increased 2- to 4- fold. The concentration of collagen in myocardial tissue correlates well (r = 0.947) with the degree of fibrosis determined by conventional histological techniques. This work represents (1) a more direct biochemical determina- tion of contractile protein concentration in whole myocardium and (2) a more direct correlation of the biochemical assay for collagen with histological data than have been reported previously. RECENT REPORTS of improved cardiac biopsy tech- niques, 1 ~ 5 coupled with the need for improved quantita- tive methods for the diagnosis of cardiomyopathies, give impetus to the development of new microanalytical meth- ods for the biochemical characterization of cardiac tissue. The technique of amino acid analysis and electrophoresis are particularly suited to this problem not only because commercially available instrumentation can detect nanom- olar quantities of specific amino acids and microgram quantities of specific proteins but also because such anal- yses of milligram quantities (wet mass) of tissue should distinguish among normal and several disease states. The present work involves (1) the adaptation of these methods to the study of cardiac tissue in animal models and (2) the use of the refined techniques to establish normal values for both actomyosin and collagen in human myocardium and to survey a variety of disease states for characteristic concentrations of these proteins in human tissue. In early investigations, the contractile protein content of whole myocardium is explicitly or implicitly assumed to be noncollagenous protein. 11 " 9 More recent methods 10 "" have included fractionation procedures which not only require an order of magnitude more tissue than that

The structural proteins of normal and diseased human myocardium.