John C. Barbato

Rapid Effects of Aldosterone and Spironolactone in the Isolated Working Rat Heart

Chronic administration of aldosterone promotes myocardial fibrosis in rats. The Randomized Aldactone Evaluation Study reported that the aldosterone antagonist spironolactone improved outcome in patients with congestive heart failure, suggesting a deleterious effect of aldosterone in the heart. Aldosterone has been shown to have rapid nongenomic effects in different tissues including the heart. However, the hemodynamic actions of aldosterone and spironolactone are not well characterized. In this study, we examined the hemodynamic effects of aldosterone and its receptor antagonist, spironolactone, in the isolated rat heart by use of the Langendorff-Neely technique. Perfusion with 10 nmol/L aldosterone increased contractility by 45% within 2 to 4 minutes (P <0.01). Similar to the aldosterone effect, 10 nmol/L spironolactone increased contractility by 41% (P <0.01). Furthermore, 100-fold molar excess of spironolactone did not block the aldosterone effect. Perfusion of aldosterone plus spironolactone resulted in the highest increase in contractility 106% (P <0.01). The threshold response for aldosterone occurred within physiological concentrations (0.5 to 1 nmol/L), and maximal contractility was achieved with 10 nmol/L aldosterone. For spironolactone, the threshold and maximal contractile responses occurred at concentrations readily achieved with clinical dosing, 0.1 to 0.5 nmol/L and 1.0 nmol/L, respectively. These data demonstrate that aldosterone and spironolactone have rapid, positive inotropic actions on the myocardium. Moreover, addition of spironolactone to aldosterone increased contractility beyond the maximal responses elicited by each agent when perfused alone, thus suggesting different pathways of action. Furthermore, the intrinsic inotropic effects of spironolactone might be relevant to the apparent beneficial effect this compound has in patients with congestive heart failure.

Molecular targeting by homocysteine: a mechanism for vascular pathogenesis

Abstract Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Although there is a growing body of evidence that homocysteine plays a causal role in atherogenesis, specific mechanisms to explain the underlying pathology have remained elusive. This review focuses on chemistry unique to the homocysteine molecule to explain its inherent cytotoxicity. Thus, the high pKa of the sulfhydryl group (pKa=10.0) of homocysteine underlies its ability to form stable disulfide bonds with protein cysteine residues, and in the process, alters or impairs the function of the protein. Albumin, fibronectin, transthyretin, annexin II, and factor V have now been identified as molecular targets for homocysteine, and in the case of albumin, the mechanism of targeting has been elucidated.

Mechanisms for Aldosterone and Spironolactone-Induced Positive Inotropic Actions in the Rat Heart

Previously, we reported that aldosterone and spironolactone have inotropic effects in the isolated perfused heart. To address the mechanisms underlying these inotropic effects, we examined the effects of aldosterone and spironolactone on isolated cardiac myocyte shortening, intracellular calcium ([Ca+2]i), pHi, and calcium-dependent actinomyosin ATPase activity. Aldosterone significantly increased shortening in cardiac myocytes (8.0±1.0 versus 16.0±1.3%, P<0.01) but neither diastolic [Ca+2]i (61.0±1.1 versus 66.0±4.4 nmol/L) nor peak systolic [Ca+2]i (302±11 versus 304±17 nmol/L) was affected. Spironolactone-increased shortening was also not coupled with changes in peak systolic calcium; however, diastolic calcium was significantly increased by spironolactone. Aldosterone, but not spironolactone, increased pHi from 7.23±0.03 to 7.59±0.02 (P<0.01); this was completely blocked by coadministration of 100 &mgr;mol/L of ethyl-isopropyl amiloride (EIPA), an inhibitor of the Na+/H+ exchanger (P<0.01). Consistent with this finding, aldosterone increased cytosolic sodium concentration ([Na+]i) from 9.2±0.15 to 11.4±0.2 mmol/L and produced a leftward shift in the pCa ATPase curve (pCa=5.82±0.02 versus 6.35±0.02, P<0.01) without affecting maximal myosin ATPase activity. Conversely, spironolactone, but not aldosterone, significantly increases maximal actomyosin ATPase activity (837±59 versus 355±52 nmol inorganic phosphate (Pi) · min−1 · g tissue−1). Collectively, these data strongly suggest that the inotropic actions of aldosterone and spironolactone are caused by different mechanisms of action. Aldosterone appeared to increase inotropy primarily through increased cytosolic pH, whereas spironolactone increased myosin ATPase calcium sensitivity and diastolic calcium concentration.

Cardiac performance in inbred rat genetic models of low and high running capacity

1 Previous work demonstrating that DA inbred rats are superior to COP inbred rats in aerobic treadmill running capacity has indicated their utility as genetic models to explore this trait. We tested the general hypothesis that intermediate phenotypes of cardiac function and calcium metabolism are responsible for the difference in capacity between these strains. 2 Logical cardiac trait differences were estimated at a tissue (isolated papillary muscle), cellular (isolated left ventricular cells), and biochemical level of organization. 3 DA hearts were found to give significantly higher values than COP hearts for: (1) maximal developed tension (38.3 % greater), and rates of tension change in contraction (61 %) or relaxation (59 %) of isolated papillary muscle, (2) fractional shortening (50 %), amplitude of the Ca2+ transient (78.6 %), and caffeine‐induced release of Ca2+ from the sarcoplasmic reticulum (SR; 260 %) in isolated ventricular myocytes, and (3) Na+,K+‐ATPase activity of isolated myocytes (17.3 %). 4 Our results suggest that these trait differences may prove useful for further studies into the genes responsible for natural variations in both ventricular function and aerobic endurance capacity. Understanding the genetic basis of aerobic capacity will help define the continuum between health and disease.

Have No Fear, MitoQ10 Is Here

The physical manifestation of a trait is a constant interplay between one’s genetic makeup and environmental factors. This notion has been substantiated by nutrigenomic studies demonstrating the benefits of nutritional supplements along the continuum between health and disease.1 More importantly, these studies have revealed the plasticity by which the genetic substrate can interact with various environmental components to either exacerbate or mitigate the manifestation of a disease process in those genetically predisposed. Focusing on cardiovascular disease, a vast literature has demonstrated that this disease process is associated with impaired energy production, increased oxidative stress, and cell calcium overload. To these ends, both clinical and animal studies have demonstrated nutrient deficiencies, integral to these processes, to be associated with cardiovascular disease and that these deficiencies represent independent predictors of increased morbidity and mortality.2,3 One cellular component that has received considerable attention regarding function and nutrient supplementation is the mitochondria. Mitochondria are responsible for cellular bioenergetics via oxidative phosphorylation. However, the perpetual transfer of electrons from one molecule to another within the mitochondria renders this organelle a major site for the genesis of reactive oxygen species (ROS).4 Although the mitochondria have antioxidant defenses,4 the disequilibrium between ROS production and ROS neutralization paves the way for disease manifestation. ROS damage to mitochondrial proteins, lipids, and DNA poses …

Estrogen Receptor Activation—Good, Aldosterone Receptor Blockade—Beneficial, Communication Between Receptors…Priceless

Steroid receptors are essentially transcription factors. When estrogens activate estrogen receptors (ERs) and aldosterone activates the mineralocorticoid receptor (MR) these steroid-receptor complexes enter the nucleus. On entry, these complexes bind to their respective response elements leading to the regulation of gene expression. This transcriptional regulation of key genes in target tissues yields relevant reproductive and endocrine functions. Because ER and MR are expressed in cardiac myocytes, fibroblasts, and vascular cells, genes essential to cardiovascular function and cardiovascular pathophysiology are regulated by aldosterone and estrogens.1,2 The consensus from research on cardiovascular tissue focusing on estrogens is that ER activation is beneficial. Specifically, ER activation has been suggested to attenuate mitogen-activated protein kinase growth signaling in response to pressure overload, increase endothelial NO synthesis, reduce vascular cell proliferation, and decrease endothelin expression.1 In addition, blunted hypertrophic responses in female mice lacking the ryanodine receptor-associated protein and guanylyl cyclase-A receptor suggest that estrogens may attenuate calcineurin/nuclear factor-activated T-cell signaling and or mediate downstream signaling in the atrial natriuretic peptide-guanylyl cyclase cascade.3,4 Whereas ER activation with specific and nonspecific estrogen agonists produce molecular responses favoring cardiovascular protection, the contrary has been demonstrated with studies examining MR activation. …