[Alterations in aortic vasomotor function in rats with chronic heart failure and its mechanism]

The aim of the present study was to investigate the alterations in thoracic aortic vasomotor function in rats with chronic heart failure (CHF) post myocardial infarction (MI), and then explored the possible mechanism of pathological changes. Male Sprague-Dawley rats were divided into sham and CHF groups randomly. The CHF model group of rats was generated by ligating the left anterior descending artery. In sham-operated rats the ligation was placed but not tightened. A total of 20 rats underwent either sham-operated (n=8) or surgery for MI (n=12). All sham-operated rats survived the surgical procedure and the post-surgical period, whereas total mortality among MI-rats was 25% (3 out of 12). Only MI-rats with infarct-size >30% of the left ventricle (LV) were included for analysis (8 out of 9). Ten weeks after surgery, rats were anaesthetized for hemodynamic measurements, which contains systolic pressure, diastolic pressure, left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), LV+dp/dt(max) and LV-dp/dt(max). After that hearts were rapidly excised and weighed. Myocardial infarct size was determined by triphenyltetrazolium chloride (TTC) staining method. Isolated thoracic artery ring preparations were studied in a wire-myograph. The arterial constrictive responses to KCl, CaCl2, phenylephrine (PE), and caffeine and the arterial diastolic responses to acetylcholine (ACh) were recorded by the Multi Myograph System. To explore the possible mechanism, nitric oxide synthase (NOS) inhibitor N-nitrl-L-arginine methylester (L-NAME) and non-selective cyclooxygenase (COX) inhibitor indomethacin (Indo) were used. The results obtained were as follows: (1) CHF group showed an increased contraction response to KCl (5-100 mmol/L) and PE (1x10(-8)-3x10(-4) mol/L), and a reduced endothelium-dependent relaxation response to ACh (1x10(-12)-1x10(-4) mol/L) compared with those observed in sham group (P<0.01, P<0.05); (2) In the presence of L-NAME (1 mmol/L), the endothelium-dependent cumulative contractions to ACh (1x10(-7)-1x 10(-4) mol/L) was significantly enhanced in CHF group (P<0.05), and this effect was reversed by pretreatment with Indo (10 mumol/L); (3) In CHF group, the vessels incubated with Indo (10 mumol/L) showed an increased vasodilation induced by ACh (1x10(-12)-1x10(-4) mol/L) (P<0.05); (4) In the Ca(2+)-free K-H solution, calcium-dependent contraction curves induced by CaCl2 (1x10(-4)-3x10(-2) mol/L) in CHF group significantly shifted to the left compared with sham group (P<0.05); while the vascular contraction induced by caffeine (30 mmol/L) had no significant changes. These findings suggest that thoracic arteries of rats with CHF have endothelial dysfunction, and the contribution of endothelial dilation and contraction was significantly altered in CHF rats. The mechanism could be partly associated with the increased endothelium-dependent contracting factors by COX pathway, or the increased extracellular Ca(2+) influx through voltage-operated channels, thus leading to elevated vasoconstriction.