Myocardial collagen in different forms of heart hypertrophy in the rat.

The hydroxyproline concentration, representing collagen content, has been investigated in normal and hypertrophied rat hearts. Enlargement of the heart was produced by four methods: a. Experimental renal hypertension (Goldblatt rats); b. Spontaneous hypertension (SHR); c. Experimental aortic stenosis; d. Swimming training. In spontaneously hypertensive rats the free wall of the right and left ventricles and the septum were analyzed separately. Furthermore, the left ventricular free wall was divided into endomyocardial and epimyocardial slices to permit separate investigation. Otherwise, the hydroxyproline concentration was always analyzed in left ventricular tissue. In swimming rats the absolute enlargement was very slight (15%), whereas the hydroxyproline concentration remained unchanged. The degree of hypertrophy was greater in all other experimental animals and was associated with an increase in hydroxyproline concentration in hypertrophied tissue. There was a positive correlation between the rate of hydroxyproline concentration increase and the degree of hypertrophy. The findings only vary in different experimental groups of Goldblatt rats at an early stage. Four weeks after surgery we found a left ventricular hypertrophy of 34%, whereas hydroxyproline concentration in left ventricular tissue was unchanged in comparison to control values. In spontaneously hypertensive rats the increase in hydroxyproline concentration in endomyocardial areas was considerably greater than in epimyocardial areas. Significant differences in water retention and nitrogen content (microgram/mg dry tissue) of hypertrophied and normal ventricular tissue were not found.