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EXPERIMENTAL STUDIES

Modulation of in vivo cardiac hypertrophy with insulin-like growth factor-1 and angiotensin-converting enzyme inhibitor: relationship between change in myosin isoform and progression of left ventricular dysfunction

^a Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan

Manuscript received March 8, 1999; revised manuscript received February 16, 2000, accepted April 5, 2000.

Reprint requests and correspondence: Dr. Yasuki Kihara, Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, 54 Shogoin Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan
kihara{at}kuhp.kyoto-u.ac.jp

OBJECTIVES

Supplemental myocardial hypertrophy induced by insulin-like growth factor (IGF)-1 may prevent transition from hypertrophy to heart failure under chronic mechanical overload.

BACKGROUND

Several studies have suggested that IGF-1 treatment may be beneficial in chronic heart failure. In addition, recent studies indicated that the amount of -myosin heavy chain (MHC) plays a significant hemodynamic role in large animals including humans.

METHODS

We treated Dahl salt-sensitive hypertensive rats on a long-term basis with IGF-1. The effects were compared with those produced by treatment using a sub-antihypertensive dose of temocapril, an angiotensin-converting enzyme (ACE) inhibitor. At 11 weeks, when these rats displayed compensated left ventricular hypertrophy (LVH), they were randomized to three groups: 1) IGF group (3 mg/kg/day); 2) temocapril group (1 mg/kg/day); and 3) vehicle (control) group.

RESULTS

After 15 weeks, the control rats showed left ventricular (LV) enlargement and severe LV dysfunction and rapidly died of pulmonary congestion (mean survival time: 16.8 ± 0.5 weeks). The survival time was significantly shortened (15.6 ± 0.3 weeks) in the IGF-1 group but significantly prolonged (19.5 ± 0.6 weeks) in the temocapril group. The rats in the IGF-1 group showed accelerated LV dilation and dysfunction. Of the several parameters investigated, it was found that the relative amounts of MHC isoforms differed among the three groups. The -MHC mRNA level was decreased by 52% (p < 0.01) in the IGF group, while it increased by 58% (p < 0.01) in the temocapril group compared with the control group. These changes were related to the progression of LV dysfunction.

CONCLUSIONS

Supplemental myocardial hypertrophy with long-term IGF-1 treatment may not be beneficial if concentric LVH already exists. Our data suggest that IGF-1 may not protect myocardial performance when its hypertrophic effect aggravates the reduction of -MHC. By contrast, the ACE inhibitor may improve myocardial function and prognosis by preventing the down-regulation of this isoform.

Abbreviations and Acronyms   ACE = angiotensin-converting enzyme   AT-II = angiotensin-II   DS = Dahl salt-sensitive   FS = fractional shortening   GAPDH = glyceraldehyde-3-phosphate dehydrogenase   GH = growth hormone   IGF = insulin-like growth factor   LVH = left ventricular hypertrophy   MHC = myosin heavy chain   RWT = relative wall thickness   SERCA = sarcoplasmic reticulum Ca2+ ATPase

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