Effects of Chronic Angiotensin-converting Enzyme Inhibition on Left Ventricular and Myocyte Structure and Function During Recovery From Chronic Rapid Pacing

LV and myocyte function and angiotensin converting enzyme (ACE) activity with ACE inhibitor (ACEI) treatment were examined in four groups of dogs (n=6 each): (1) control; (2) with 4 weeks of recovery from chronic rapid pacing (REC; 216 beats/min), (3) ACEI for the first 14 days of REC (ACEI—14), and (4) ACEI for 28 days of REC (ACEI—28). Three additional control dogs were administered ACEI for 28 days. LV mass increased with REC compared to control (146±6v92±3 g,P<0.05), was unaffected with ACEI—14, and was decreased with ACEI—28 compared to REC (111±8 g,P<0.05). Myocyte function was decreased in REC compared to controls (43±3v63±3μ m/s,P<0.05) and was similarly reduced with ACEI—14. However, with ACEI—28, myocyte shortening velocity was increased compared to REC (56±1μ m/s,P<0.05). Myocyteβ -adrenergic response was decreased with REC and ACEI—14 compared to controls (53±9 and 57±14, respectivelyv127±14μ m/s,P<0.05). ACEI—28 resulted in a normalization of myocyteβ -adrenergic responsiveness (108±3 μ m/s). LV myocardial ACE activity increased in REC compared to control (5.82±0.21v3.51±0.15 nmol/mg/min,P<0.05). With ACEI—14 or ACEI—28, myocardial ACE activity was decreased compared to REC (4.16±0.06 and 4.08±0.23 nmol/mg/min;P<0.05). In control dogs administered ACEI, there were no differences in any of these parameters compared to controls. The unique findings in this study were: (1) effects of ACEI treatment in this model of LV hypertrophy were time dependent with respect to LV mass and LV and myocyte function; and (2) the effect of ACEI treatment on the degree of LV hypertrophy appears to not be solely due modulation of myocardial ACE activity.