Geir Christensen

Pulmonary and cardiac expression of preproendothelin-1 mRNA are increased in heart failure after myocardial infarction in rats. Localization of preproendothelin-1 mRNA and endothelin peptide.

OBJECTIVESnRecent reports indicate that endothelin (ET) plays an important pathophysiological role in congestive heart failure (CHF). However, existing data on local cardiopulmonary ET production are few. No studies have hitherto examined the specific anatomic localization of cardiopulmonary ET synthesis in CHF. Thus, the aims of the present study were to examine whether cardiopulmonary preproET-1 mRNA synthesis is upregulated in CHF and to determine the anatomic localization of preproET-1 mRNA and the mature peptide.nnnMETHODSnCHF was induced in rats by occluding the left coronary artery. Only animals with a left ventricular end-diastolic pressure above 15 mmHg after one week were included (n = 28). Sham-operated animals served as controls (n = 24). Hearts and lungs were examined by mRNA slot blot analyses, in situ hybridization (ISH) and immunohistochemistry (IHC).nnnRESULTSnIn CHF-rats, slot blot analyses revealed a 3.5 +/- 1.1-fold and a 6.4 +/- 0.8-fold upregulation of preproET-1 mRNA in the noninfarcted and the infarcted area of the left ventricles, respectively (p < 0.05 for both). ISH revealed that the preproET-1 mRNA was localized predominantly over the granulation tissue in the infarcted region. The ET peptide was predominantly localized to inflammatory cells and remaining cardiomyocytes in the infarcted region as determined by IHC. Lungs from CHF-rats showed a 1.5 +/- 0.1-fold upregulation of preproET-1 mRNA (p = 0.01). The most abundant preproET-1 mRNA and ET-1-like-immunoreactivity (ET-1-ir) was seen over inflammatory cells and over airway epithelial cells. Some ET-1-ir was also located to bronchial and vascular smooth muscle cells.nnnCONCLUSIONnIncreased cardiopulmonary ET synthesis strongly suggest a pathophysiological role for ET in CHF.

Electrical stimulation of adult rat cardiomyocytes in culture improves contractile properties and is associated with altered calcium handling.

A major limitation in long-term studies of quiescent adult cadiomyocytes in culture has been the decline in contractile properties of the cells over time. Regular contracting cardiomyocyte cultures may represent a more physiological model. The aim of the present study was to investigate the mechanical properties and calcium handling of myocytes after 24 hours of electrical stimulation at 1 Hz. In a random and blind design, stimulated (S) and unstimulated (U) myocytes were examined using an inverted microscope which allows continuous length recordings and measurements of intracellular Ca2+. Fractional shortening examined at 0.25 Hz was 14.67±0.51 % in S cells and was not significantly different from U cells. However, at higher frequencies we found a significant difference in mechanical properties between the two groups. At 2 Hz fractional shortening was 12.03±0.67 % in S cells, but only 8.07±0.94 % U cells (P<0.05). We were able to abolish the difference between the two groups by stimulating with the β-adrenergic agonist isoproterenol. Measurements of Ca2+ transients were made at 1 Hz after loading with fura 2-AM. Peak fura 2 ratio was 25.4% greater in S cell compared to U cells. Resting fura ratios were not significantly different. Caffeine-induced transients were greater in S than in U cells. [3H]-ryanodine-binding and Ca2+-ATPase contents were not significantly different. In conclusion, we have found that regular electrical stimulation of adult ventricular myocytes in culture, so that they contract rhythmically, enhances both mechanical properties and calcium transients when compared to quiescent myocytes. These results suggest that regular electrical stimulation is important when studying the function of adult ventricular myocytes in culture.

Quantitative Assessment of Myocardial Perfusion During Graded Coronary Artery Stenoses by Intravenous Myocardial Contrast Echocardiography

OBJECTIVESnThe purpose of this study was to examine whether coronary stenoses of variable severity could be quantitatively assessed by analysis of myocardial perfusion as determined by intravenous (IV) myocardial contrast echocardiography.nnnBACKGROUNDnRecently, new contrast agents and imaging technology have been developed that may enable improved assessment of myocardial perfusion by IV contrast injection.nnnMETHODSnVariable obstruction of the left anterior descending (LAD) coronary artery in dogs was produced by a screw occluder. Coronary artery flow was measured with a transit time flowmeter during baseline, pharmacological vasodilation, a non-flow-limiting stenosis at rest in conjunction with vasodilation, a flow-limiting stenosis, and total occlusion. Myocardial contrast echocardiography was performed after IV injection of the contrast agent NC 100100. Time-intensity curves were obtained off-line for the LAD risk area and the adjacent left circumflex (LCx) territory, and peak background-subtracted video intensity was determined. Fluorescent microspheres were injected at each intervention for determination of regional myocardial blood flow.nnnRESULTSnDuring non-flow-limiting stenosis, flow limiting stenosis and total occlusion, LAD/LCx ratios of peak myocardial videointensity and blood flow decreased proportionately. Both LAD/LCx ratios of video intensity and blood flow identified the non-flow-limiting and the flow-limiting stenoses as well as total occlusion of the LAD artery. A significant correlation between LAD/LCx video intensity and blood flow ratios was observed (r = 0.83, p < 0.0001).nnnCONCLUSIONSnThe degree of blood flow mismatch between ischemic and normal myocardial regions during graded coronary stenoses can be estimated in the dog by quantitative assessment of myocardial perfusion produced by IV myocardial contrast echocardiography.