摘要:

This study was performed to examine the transmural (endocardial vs. epicardial) heterogeneity of myocardial blood flow during the cardiac cycle (systole vs. diastole). Twenty-four contrast echocardiographic injections were performed in seven open-chest anesthetized dogs either into left anterior descending or circumflex coronary artery or into the aortic root. Two-dimensional echocardiography in short-axis view was performed and was digitized off-line into a 256 × 256 pixel matrix with 256 gray levels/pixel. All end-diastolic and end-systolic frames before and to peak contrast were analyzed. A region of interest corresponding to the most intensely opacified myocardial segment was traced, the mean videodensity measured, and the frame of initial contrast appearance detected. The region of interest was divided into three equal parallel layers corresponding to the endocardial, midcardial, and epicardial myocardium. When the echocardiographic contrast effect initially appeared in diastole, the increment in videodensity was greater for the endocardium (131±48%) than for the epicardium (71±37% of the increment in videodensity of the entire wall) (p< 0.05). This inhomogeneity subsequently disappeared in the following end-systolic frame. When the initial echocardiographic contrast effect appeared in systole, intensity was higher in epicardium (136±83%) than in endocardium (60±60%) (p< 0.05). However, in the following diastole, intensity was not significantly different for the two layers. Thus, myocardial contrast echocardiography demonstrates that coronary blood flow is primarily subendocardial in distribution during diastole and subepicardial during systole.

ISSN:0009-7322    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

N-acetylcysteine is assumed to reverse nitrate tolerance by replenishing depleted intracellular sulfhydryl groups, but data on interactions ofN-acetylcysteine and nitrates in patients with stable angina are controversial and disappointing. Therefore, we studied the effect ofNacetylcysteine on nitrate responsiveness of epicardial arteries and of the venous system (assessed as changes in effective vascular compliance) in dogs (n= 12) during long-term nitroglycerin treatment (1.5,g/kg/min i.v. for 5–6 days). In dogs with nitroglycerin-specific tolerance (shift of venous or epicardial artery dilation to 15-17-fold higher dosages), N-acetylcysteine (100 mg/ kg i.v.) had no dilator effect and did not alter the dose-response relations of nitroglycerin. Yet, in nontolerant dogs (n= 17),N-acetylcysteine augmented (1.5–2.0-fold) the dilation of epicardial arteries and the reduction of peripheral vascular resistance induced by 0.5–1.5 μg/kg/min nitroglycerin. In vitro, the augmentation of purified guanylate cyclase activity by nitroglycerin (10–100 μM) was potentiated byN-acetylcysteine (0.01–1.0 mM) in saline or in canine plasma, butN-acetylcysteine alone was ineffective. We conclude that 1)N-acetylcysteine does not restore nitroglycerin responsiveness in tolerant epicardial arteries or veins in vivo, 2) a small, tolerance-independent augmentation of nitroglycerin-induced dilation may result from Nacetylcysteine–induced extracellular formation of a stimulant of guanylate cyclase from nitroglycerin.

ISSN:0009-7322    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1989

数据来源: OVID