Relation between ventricular DNA content and number of myocytes and non-myocytes in hearts of normotensive and spontaneously hypertensive rats.

Myocardial DNA concentration and ventricular weight were measured in the hearts of normal and spontaneously hypertensive rats varying in age from 1 day to 1 year and the ventricular DNA content calculated. A linear relation between ventricular DNA content and ventricular weight was observed in both rat strains. This linear relation was deduced theoretically, assuming that the number of ventricular non-myocytes per heart was proportional to ventricular weight and that the number of ventricular myocytes per heart was constant after the first postnatal week. The fit with experimental data produced values of the number of ventricular myocytes (42.5 X 10(6] and non-myocytes (199 X 10(6) per gram of ventricular tissue) in normal rat heart. Using published data on ventricular volume occupied by myocytes (80%) and myocardial specific density (1.06 g X ml-1), the mean(SD) volume of individual myocytes could be calculated (17758(2632) multiplied by ventricular weight, expressed in micron 3 X g). The values obtained compared well with experimental observations reported in the present study (18504(131) micron 3 X g) and in other studies. Hearts from spontaneously hypertensive rats had lower numbers of myocytes (37.4 X 10(6] and non-myocytes (180 X 10(6) per gram) per heart than normal hearts with identical ventricular weights. Hearts of normal 2 month old rats that were made hypertrophic by various means were identical to non-hypertrophic hearts of normal older rats with identical ventricular weights in relation to the number of ventricular myocytes and non-myocytes per heart. It is concluded that ventricular hypertrophy induced in young adult rats might be regarded as normal growth occurring at an accelerated rate.