GROWTH-HORMONE ATTENUATES EARLY LEFT-VENTRICULAR REMODELING AND IMPROVES CARDIAC-FUNCTION IN RATS WITH LARGE MYOCARDIAL-INFARCTION

Objectives. We sought to investigate the cardiac effects of growth hor mone (GB) administration during the early phase of pathologic remodeli ng in a rat model of large myocardial infarction (MI). Background. Rec ent evidence suggests that exogenous administration of GH. evokes a hy pertrophic response and increases left ventricular (LV) function in vi vo in rats with normal or chronically failing hearts. We hypothesized that these effects would attenuate ventricular remodeling early after MI. Methods. Fifty-eight male rats underwent sham operation (n = 19) o r had induced MI (n = 39). The day after the operation, the infarcted rats were randomized to receive 3 weeks of treatment with GH, 3 mg/kg body weight per day (n = 19) or placebo (n = 20). Echocardiography, ca theterization and isolated whole heart preparations were used to defin e cardiac structure and function. Results. Growth hormone caused hyper trophy of the noninfarcted myocardium in a concentric pattern, as note d by higher echocardiographic relative wall thickness at 3 weeks and b y morphometric histologic examination. Left ventricular dilation was r educed in the GH-treated versus placebo group (echocardiographic LV di astolic diameter to body weight ratio 2.9 +/- 0.1 vs. 3.5 +/- 0.2 cm/k g; p < 0.05). In vivo and in vitro cardiac function was improved after GH treatment. Despite elevated insulin-like growth factor-1 (IGF-1) s erum levels in GH-treated rats, myocardial IGF-1 messenger ribonucleic acid was not different among the three groups, suggesting that an inc rease in its local expression does not appear necessary to yield the o bserved effects. Conclusions. These data demonstrate that early treatm ent of large MI with GH attenuates the early pathologic LV remodeling and improves LV function. (C)1997 by the American College of Cardiolog y.