REGRESSION OF MYOCARDIAL HYPERTROPHY

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Regression of hypertrophy was studied in 96 adult rats following aortic debanding (dB). Controls were 146 continuously banded (B), and 116 sham-operated (S) rats. Sacrifice was at 3, 7, 14, 21 and 28 days for LV mass, RNA, DNA and hydroxyproline (OHP). Hemodynamics were obtained at 28 days. Aortic gradients were 60-130 mmHg in B, and none in dB and S. Initial (dP/dt)p−1, in Sec−1, was lower in dB (212) than in B (235) and S (234) although not significantly. Early debanding (after 10 days of aortic constriction) showed drop in LV mass from 35% to 11% above C (P<0.001), and fall in RNA from 37% to 19% above S (P<0.05), by 3 days; thereafter dB and S values were comparable. However, DNA in dB was 32% above S (P<0.01) at 10 days, and 12% above S at 28 days (P=n.s.). Corresponding OHP levels in dB were 90% above S (P<0.001), and 80% (P<0.025) above S, respectively. Late debanding (after 28 days constriction) showed LV mass in dB still 12% above S (P<0.025) at 21 days; RNA was 34% above S (P<0.01) at 14 days. DNA and OHP remained elevated throughout the study period in dB-25% (P<0.02) and 118% (P<0.001) above S at 28 days. LV mass, RNA, DNA and OHP in B remained consistently high. Although mass and RNA regress after relief of pressure overload, the connective tissue, as measured by DNA and OHP, doesnot do so readily. Its regression is influenced by the duration of cardiac stress.