Contracture type and fibrosis type of decreased myocardial distensibility. Different changes in elasticity of myocardium in hypoxia and hypertrophy.

Resting length-tension relationships were measured in rat trabecular muscle strips under control (O2) and contracture (N2) conditions as well as in preparations of Goldblatt II (8-week stage) and control rats. For the evaluation of the diastolic elastic properties, diastolic stress at 1max, stress-strain relationships, the relation between tangent modulus delta sigma divided by delta epsilon and stress sigma, and the function ln stress sigma = f (strain epsilon) were calculated and plotted. It was shown that the hypoxic contracture corresponds to the calcium-caffeine contracture--an experimental contracture model already investigated earlier. In contrast to these contracture-induced alterations, Goldblatt II hypertrophied myocardium corresponded to the fibrosis type. This type was already analyzed in an experimental model of myocardium-tendon tandem preparation. Additional investigations of hydroxyproline concentration of the same biological material showed in contrast to other studies that the collagen content may already be increased in this early stage of hypertrophy. Thus, altered distensibility of Goldblatt myocardium is certainly primarily due to increased connective tissue content.