Ventricular pacing leads to a dilated myopathy in which cell death and myocyte hypertrophy predominate. Because angiotensin II (Ang II) stimulates myocyte growth and triggers apoptosis, we tested whether canine myocytes express the components of the renin-angiotensin system (RAS) and whether the local RAS is upregulated with heart failure. p53 modulates transcription of angiotensinogen (Aogen) and AT(1) receptors in myocytes, raising the possibility that enhanced p53 function in the decompensated heart potentiates Ang II synthesis and Ang II-mediated responses. Therefore, the presence of mRNA transcripts for Aogen, renin, angiotensin-converting enzyme, chymase, and AT(1) and AT(2) receptors was evaluated by reverse transcriptase-polymerase chain reaction in myocytes. Changes in the protein expression of these genes were then determined by Western blot in myocytes from control dogs and dogs affected by congestive heart failure. p53 binding to the promoter of Aogen and AT(1) receptor was also determined. Ang II in myocytes was measured by ELISA and by immunocytochemistry and confocal microscopy. Myocytes expressed mRNAs for all the constituents of RAS, and heart failure was characterized by increased p53 DNA binding to Aogen and AT(1). Additionally, protein levels of Aogen, renin, cathepsin D, angiotensin-converting enzyme, and AT(1) were markedly increased in paced myocytes. Conversely, chymase and AT(2) proteins were not altered. Ang II quantity and labeling of myocytes increased significantly with cardiac decompensation. In conclusion, dog myocytes synthesize Ang II, and activation of p53 function with ventricular pacing upregulates the myocyte RAS and the generation and secretion of Ang II. Ang II may promote myocyte growth and death, contributing to the development of heart failure.

Although the role of nitric oxide (NO) in the modulation of vascular tone has been studied and well understood, its potential role in the control of myocardial metabolism is only recently evident. Several lines of evidence indicate that NO regulates myocardial glucose metabolism; however, the details and mechanisms responsible are still unknown. The aim of this study was to further define the role of NO in the control of myocardial glucose metabolism and the nitric oxide synthase (NOS) isoform responsible using transgenic animals lacking endothelial NOS (ecNOS). In the present study, we examined the regulation of myocardial glucose uptake using isometrically contracting Langendorff-perfused hearts from normal mice (C57BL/6J), mice with defects in the expression of ecNOS [ecNOS (-/-)], and its heterozygote [ecNOS (+/-)], and wild-type mice [ecNOS (+/+)] (n=6, respectively). In hearts from normal mice, little myocardial glucose uptake was observed. This myocardial glucose uptake increased significantly in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME). Similarly, in the hearts from ecNOS (-/-), glucose uptake was much greater than in normal mice, whereas myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice was not different from normal mice. In addition, myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice increased significantly in the presence of L-NAME. At a workload of 800 g. beats/min, L-NAME increased glucose uptake from 0.1+/-0.1 to 3+/-0.4 microg/min x mg in ecNOS (+/-) mice and from 0.2+/-0.1 to 2.7+/-0.7 microg/min x mg in ecNOS (+/+) mice. Furthermore, in the hearts from ecNOS (-/-) mice, 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cGMP), a cGMP analog or S-nitroso-N-acetylpenicillamine (SNAP), a NO donor essentially shut off glucose uptake, and in hearts from ecNOS (+/-) mice, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), an inhibitor of cGMP, increased the glucose uptake significantly. These results indicate clearly that cardiac NO production regulates myocardial glucose uptake via a cGMP-dependent mechanism and strongly suggest that ecNOS plays a pivotal role in this regulation. These findings may be important in the understanding of the pathogenesis of the diseases such as ischemic heart disease, heart failure, diabetes mellitus, hypertension, and hypercholesterolemia, in which NO synthesis is altered and substrate utilization by the heart changes.

The increased NO induction in failing myocytes does not alter baseline sarcomere mechanics but attenuates the positive inotropic response to isoproterenol. Thus, myocyte NO plays an important role in the autocrine regulation of the contractile function of myocytes in congestive heart failure.