Activation of cardiorenal and pulmonary tissue endothelin-1 in experimental heart failure

Proteomic profiling implies mitochondrial dysfunction in tachycardia-induced heart failure

BACKGROUND/OBJECTIVES

Molecular mechanisms of congestive heart failure as reflected by alterations of protein expression patterns are still incompletely analyzed. We therefore investigated intraventricular (ie, left ventricular congestive heart failure [LV-CHF] vs. LV-control [CTRL], and right ventricular [RV]-CHF vs. RV-CTRL) and interventricular (ie, LV-CHF vs. RV-CHF, and LV-CTRL vs. RV-CTRL) protein expression differences in an animal model.

METHODS

The model of rapid ventricular pacing in rabbits was combined with a proteomic approach using 2-dimensional gel electrophoresis. Identification of proteins was done by matrix-assisted laser desorption/ionization-tandem mass spectrometry (MALDI-MS/MS).

RESULTS

Rapid ventricular pacing-induced heart failure was characterized by LV dilatation, dysfunction, and hypotension as well as by increased BNP gene expression. By comparing LV-CHF vs. LV-CTRL, proteins were found to be underexpressed at 3 crucial points of cellular energy metabolism. In RV-CHF vs. RV-CTRL, proteins belonging to respiratory chain complexes were underexpressed, but additionally a disturbance in the nitric oxide-generating enzymatic apparatus was seen. Regarding the interventricular analyses, a stronger expression of energetic pathways was accompanied by an underexpression of contractile and stress response proteins in failing left vs. right ventricles. Finally, significant protein expression differences were found in LV-CTRL vs. RV-CTRL reflecting a higher expression of contractile, stress response, and respiratory chain proteins in LV tissue.

CONCLUSIONS

In tachycardia-induced heart failure, significant inter- and intraventricular protein expression patterns were found with a predominance of proteins, which are involved in cellular energy metabolism.

Activation of endothelin A receptors contributes to impaired responsiveness of renal mechanosensory nerves in congestive heart failure

Increasing renal pelvic pressure results in PGE2-mediated release of substance P, leading to increases in afferent renal nerve activity (ARNA) and natriuresis, that is, a renorenal reflex response. The renorenal reflexes are impaired in congestive heart failure (CHF). Impairment of the renorenal reflexes may contribute to the increased renal sympathetic nerve activity and sodium retention in CHF. Endothelin (ET)-1 contributes to the pathological changes in cardiac and renal function in CHF. Therefore, we examined whether the ETA receptor antagonist BQ123 altered the responsiveness of renal mechanosensory nerves in CHF. The ARNA responses to increasing renal pelvic pressure were suppressed in CHF but not in sham-CHF rats. In CHF, increasing renal pelvic pressure by 7.5 mm Hg before and during renal pelvic perfusion with BQ123 increased ARNA 12% +/- 3% and 21% +/- 3% (p < 0.05 vs. vehicle). In isolated renal pelvises from CHF rats, PGE2 increased substance P release from 5 +/- 0 to 7 +/- 1 pg/min without BQ123 and from 4 +/- 1 to 9 +/- 1 pg/min with BQ123 in the bath (p < 0.01 vs. vehicle). BQ123 had no effect on the ARNA responses or substance P release in sham-CHF. In conclusion, activation of ETA receptors contributes to the impaired responsiveness of renal mechanosensory nerves in CHF rats by a mechanism(s) at the renal sensory nerve endings.

Renal handling of endothelin in patients with chronic heart failure

Chronic heart failure is characterized by increased renal extraction of endothelin (ET)-1 and unaltered handling of big ET-1. The renal extraction of ET-1 in patients with heart failure is closely related to elevations in pulmonary artery and pulmonary capillary wedge pressures.

Early activation of cardiac and renal endothelin systems in experimental heart failure

We investigated the time course of the expression of cardiac and renal endothelin systems in tachycardia-induced heart failure in dogs. Eleven beagles underwent rapid pacing at a progressively increased rate over a period of 5 wk, with a weekly clinical examination, echocardiography, measurement of circulating and urinary endothelin-1 (ET-1), and myocardial and renal tissue biopsies. Real-time quantitative PCR was used for determinations of tissue prepro-ET-1 (ppET-1), ET-1-converting enzyme (ECE-1), and ETA and ETB receptor mRNA. Cardiac and renal tissue ET-1 contents were evaluated by immunostaining and measured by radioimmunoassay at autopsy. Rapid pacing caused a progressive increase in end-systolic and end-diastolic ventricular volumes (P < 0.05) from week 2 together with a decrease in ejection fraction and in mean velocity of circumferential shortening (P < 0.05) from week 1. These changes were tightly correlated to myocardial ppET-1 and renal ETA receptor mRNA and less so to myocardial ECE-1 mRNA, and they occurred before any increase in plasma and urinary ET-1 (P < 0.05 from week 4) and clinical signs of heart failure. Renal ppET-1 did not change. Both cardiac and renal ET-1 peptide contents were increased at autopsy. We conclude that tachycardia-induced heart failure in dogs is characterized by an early activation of the cardiac and renal tissue endothelin systems, which occurs before any changes in circulating and urinary ET-1 and is closely related to altered ventricular function.

Comparative Sequences of Canine and Feline Endothelin-1

BACKGROUND

Endothelin-1 (ET-1, "mature ET-1") is a potent vasoconstrictor peptide that is made along with "big ET-1" from its precursor, preproET-1. Increased plasma concentrations of ET-1 and big ET-1 occur with various forms of cardiovascular disease in humans. Our laboratory is investigating plasma endothelins as diagnostic tests of cardiovascular disease in dogs and cats; however, commercial immunoassays designed specifically for use in dogs and cats are limited.

OBJECTIVE

Amino acid sequences of feline and canine big ET-1 were obtained and used to predict antibody cross-reactivity with immunoassay test kits from other species.

METHODS

Genomic DNA was extracted from peripheral blood and total RNA was extracted from canine and feline left ventricles for reverse transcription polymerase chain reaction (PCR) and PCR amplification of segments of the canine and feline preprohormone containing the big ET-1 sequences. The derived amino acid sequences were compared with known big ET-1 and ET-1 sequences of several other species, including human, mouse, and rat.

RESULTS

Feline and canine big ET-1 had 87-97% and 89-100% homology, respectively, with that of other mammalian species. Canine ET-1 was identical to human, mouse, and rat ET-1. In contrast, the amino acid sequence of feline ET-1 was unique owing to a leucine for methionine substitution at position 7.

CONCLUSIONS

It is highly likely that anti-human and anti-rodent ET-1 antibodies will cross-react with mature canine ET-1. In contrast, antibodies to mature ET-1 intended for use with feline tissues and antibodies to big ET-1 in either dogs or cats may have partial or no cross-reactivity depending on the peptide sequences used to produce the antibodies.

Predominant activation of endothelin-dependent cardiac hypertrophy by norepinephrine in rat left ventricle

Locally released endothelin (ET)-1 has been recently identified as an important mediator of cardiac hypertrophy. It is still unclear, however, which primary stimulus specifically activates ET-dependent signaling pathways. We therefore examined in adult rats (n = 51) the effects of a selective ET(A) receptor antagonist in experimental models of cardiac hypertrophy, in which myocardial growth is predominantly initiated by a single primary stimulus. Rats were exposed to mechanical overload (ascending aortic stenosis), increased levels of circulating ANG II (ANG II infusion combined with hydralazine), or adrenergic stimulation (infusion of norepinephrine in a subpressor dose) for 7 days. All experimental treatments significantly increased left ventricular weight/body weight ratios compared with untreated rats, whereas systolic left ventricular peak pressure was increased only after ascending aortic stenosis. ET(A) receptor blockade exclusively reduced norepinephrine-induced cardiac hypertrophy and atrial natriuretic peptide gene expression. Blood pressure levels and heart rates remained unaffected during ET(A) receptor blockade in all experimental groups. These data indicate that in rat left ventricle, the ET-dependent signaling pathway leading to early development of cardiac hypertrophy and fetal gene expression is primarily activated by norepinephrine.