Endethelin-nitric-oxide interactions in congestive heart failure

The current project investigated i) the role of endothelin, a polypeptide of endothelial origin, in cardiac hypertrophy and associated cardiac dysfunction commonly observed in response to increased arterial resistance, and ii) how these changes relate to changes in myocardial calcium homeostasis. Most experiments were done on isolated perfused hearts from normotensive rats, which were injected with monocrotaline which results in pulmonary artery dysfunction and pulmonary hypertension which then secondarily provokes right ventricular enlargement and wall thickening (hypertrophy) in response to increased pulmonary artery pressure. We documented myocardial calcium levels and calcium transport kinetics in hypertrophic hearts and found that long- term ETA receptor antagonism normalizes myocardial cytosolic calcium modulation and almost completely restored cardiac function to normal. Thus, ETA receptor blockers may hold great potential as pulmonary vascular protectants and cardiac antihypertrophic agents. We initially studied the release of endothelin and its precursor, big endothelin, from normal and hypertrophic hearts, but found no difference between the groups, indicating that hypertrophic hearts produced normal amounts of the peptides. Therefore, intrinsic cardiac endothelin may not be involved in the growth process of the right heart subjected to a high work-load. Further, what little endothelin the heart produces stems mostly from endothelial, not myocardial cells, as verified by chemically de-endothelializing the hearts. However, plasma endothelin and big endothelin levels were higher in animals injected with monocrotaline, indicating that endothelin might affect heart growth as blood-borne, i. e. extra-cardiac agent (hormonal action of the peptide; see below). The experiments designed to clarify the relation between myocardial calcium cardiac dysfunction showed that hypertrophic right ventricles relaxed much more slowly than controls during diastole, which was due to slowed calcium sequestration. On the other hand, neither systolic calcium movements nor steady- state or maximal calcium levels, induced by exogenous calcium or calcium-mobilizing agonists, were changed in hypertrophy. Finally and importantly, the changes in diastolic calcium kinetics were completely prevented by an endothelin ETA recepter blocker and cardiac inotropic state and right ventricular wall stress were normalized. In addition, pulmonary artery endothelial function was significantly improved. These data show that blood-borne endothelin stimulated cardiac growth and disrupts calcium metabolism in cardiac myocytes leading to diastolic right-ventricular functional impairments, whereas preventing endothelin-induced signal transduction by chronically blocking ETA receptors prevents all deleterious effects of endothelin. These results strongly support development of endothelin ETA receptor antagonists as cardiopulmonary protectants. The data are summerized in several original publications. Other topics investigated were: - role of the endothelial cell layer in transcapillary transport of insulin. - We found in a genetic model of insulin resistance (JCR:LA-cp rats) that insulin transfer across the endothelium is substantially delayed in obese insulin- resistant rats and that it likely contributes to the postprandial alterations of glucose metabolism observed in the metabolic syndrome. - role of calcium in development of varicose veins in humans. - We observed reduced contractility of diseased human varicose veins in response to endothelin and other venoconstrictors, and that the reduced constriction involved impaired calcium mobilization. - anti-oxidant action of L-arginine. - Using parallel functional and analytical (ESR) assays we demonstrated for the first time protective effects of L-arginine against oxygen radical-induced injury by free radical scavenging. - role of endothelium in natriuretic peptide-medicated vasorelaxation. - We demonstrated for the first time that ANP- and CNP- mediated relaxation of coronary resistance vessels is partly mediated by the NO-cGMP pathway. The total number of peer-reviewed reports published on these topics was 13.