Key result
A 6-day infusion of IGF-I and GH stimulated myofibrillar gene expression, increasing beta-MHC 1.8-fold in hypophysectomized rats, and decreased ANF expression by 63% and 45% in normal rats.
IGF-I and GH stimulate the expression of myofibrillar genes and modulate ANF mRNA concentrations in rat heart ventricles in vivo, with effects dependent on the hormonal status of the animals.
We have investigated the effect of a 6-day infusion of recombinant human (rh) IGF-I (0.3-1.0 mg/day) or rhGH (200 mU/day) into normal and hypophysectomized rats on the ventricular expression of myofibrillar genes (alpha- and beta-myosin heavy chain (MHC), skeletal and cardiac alpha-actin) and of atrial natriuretic factor (ANF). In normal rats, beta-MHC was not detectable either before or after IGF-I or GH, but alpha-MHC mRNA increased significantly (twofold) with GH (not statistically significant for IGF-I). In contrast to normal rats, hypophysectomized rats did not express alpha-MHC either before or after IGF-I or GH, but beta-MHC was strongly expressed and significantly stimulated (1.8-fold) by IGF-I (not statistically significantly with GH). Skeletal alpha-actin expression remained unchanged during IGF-I or GH treatment of normal rats, but was enhanced by both IGF-I and GH (2.5- and 2.8-fold respectively) in hypophysectomized rats. Expression of cardiac alpha-actin in normal and hypophysectomized rats was not altered by either treatment. IGF-I and GH decreased ventricular expression of ANF in normal rats by 63% and 45% respectively, but did not influence ANF expression in hypophysectomized rats. Our results show that IGF-I and GH (possibly via IGF-I) stimulate expression of myofibrillar genes and modulate ANF mRNA concentrations in rat heart ventricles in vivo, depending on the hormonal status of the animals. However, neither IGF-I nor GH caused a shift from the beta- to the alpha-MHC isoform in hypophysectomized rats.
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My et al. (1997) studied Normal and hypophysectomized rats. Recombinant human (rh) IGF-I or rhGH was evaluated on Ventricular expression of myofibrillar genes (alpha- and beta-MHC, skeletal and cardiac alpha-actin) and atrial natriuretic factor (ANF). A 6-day infusion of IGF-I and GH stimulated myofibrillar gene expression, increasing beta-MHC 1.8-fold in hypophysectomized rats, and decreased ANF expression by 63% and 45% in normal rats.
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