Canine Left Coronary Artery Research Articles

Regional differences in the vasorelaxing effects of testosterone and its 5-reduced metabolites in the canine vasculature

Although the vasorelaxing effects of testosterone (T) and various androgen metabolites have been observed in a variety of blood vessels and species, previous studies have not systematically compared the vasorelaxing effects of androgen metabolites in different vascular beds within the same species. Therefore, we studied the vasorelaxing effects of T and its 5-reduced metabolites (5α- and 5β-DHT) on KCl-induced contractions of the canine left coronary artery, femoral artery and saphenous vein, using standard isometric recordings. KCl contractions were inhibited by each androgen in a concentration-dependent manner from 1.8 to 310μM. Vascular sensitivity and efficacy were expressed as inhibitory concentration 50 (IC50) and maximal relaxation (Rmax), respectively. The coronary artery was significantly more sensitive to androgen-induced vasorelaxation than the saphenous vein or femoral artery. These vasorelaxing responses were unaffected by an antiandrogen (Flutamide) or the sulfhydryl reagent, N-ethylmaleimide, suggesting a nongenomic mechanism independent of signaling mediated by the androgen receptor or G proteins. Concentration–response curves were unchanged in endothelium-denuded preparations; thus, the endothelium appears to have no role in androgen-induced vasorelaxation. 5β-DHT was the most potent androgen in both coronary and femoral artery, but all three androgens were equipotent in the saphenous vein. It is concluded that: 1) significant regional differences exist in vasorelaxing effects of androgen metabolites in the canine vasculature; 2) structural differences in these androgens determine their vasorelaxing efficacy; and 3) regional differences in androgen-induced vasorelaxation may account for some of the conflicting findings reported on the vasorelaxing effects of the androgens.

Branching Patterns of the Left Main Coronary Artery in the Dog Demonstrated by the Use of Corrosion Casting Technique

As many investigators use dogs as experimental models in catheterization-, ligation-, and collateral flow studies, knowledge and awareness of the canine left coronary artery anatomical variation is vital for differentiation between canine and human coronary arterial patterns and canine and human coronary congenital anomalies with or without circulatory importance. The present study was performed to examine and review the various principal subdivisions of the canine left main coronary artery (LMCA) in vascular casts of 20 hearts obtained from cadavers of clinically normal dogs of various ages, breeds and of either sex. A corrosion casting technique using an acrylic resin called Tensol Cement No. 70 and a lower-viscosity acrylic resin called Mercox were used to produce a three-dimensional model of the canine coronary arteries. In our study, all dog hearts were left preponderant and the patterns of the principal subdivisions of the LMCA were grouped into three types: Type 1 occurred in seven of the 20 dogs (35%), Type 2 in 12 of 20 dogs (60%) and Type 3 in one instance (5%). A comparison between the canine divisional patterns of the LMCA in the vascular casts and those reported in the literature showed major agreement.

Catheter-delivered high intensity, low frequency ultrasound induces vasodilation in vivo.

This study investigated the effect of intravascular high intensity, low frequency catheter-delivered ultrasound on vasomotor behaviour in vivo. Catheter-delivered therapeutic ultrasound induces endothelium-independent vasodilation in vitro. To study this effect in vivo we analysed the angiograms of canine coronaries and human femoropopliteal arteries before and after ultrasound exposure. Vasomotor behaviour was studied using a computer edge detection program. We analysed the angiograms of: (1) eight canine left coronary arteries before and after ultrasound; (2) eight canine left coronaries only subjected to serial angiograms, and three canine left coronary arteries of two dogs after passing the unactivated ultrasound probe down the coronary artery infusing saline at a rate of 10-20 ml.min-1, which served as controls, and (3) eight angiographically normal human arterial sites proximal to occlusions in eight femoropopliteal arteries of patients undergoing ultrasound angioplasty for peripheral vascular disease. Vessel diameter of canine coronaries after ultrasound exposure increased from 2.3 +/- 0.3 mm to 2.8 +/- 0.3 mm (21 +/- 2.3%) (P < 0.01). There was no change in vascular diameter in controls after multiple angiograms (2.4 +/- 0.3 mm vs 2.5 +/- 0.2 mm (4.2 +/- 0.2%) (P = ns). Average vessel diameter after passage of the unactivated probe with saline infusion decreased in the left anterior descending coronary artery from 3.66 mm to 3.13 mm, and in the left circumflex coronary artery from 2.88 mm to 2.62 mm. Vessel diameter in human femoropopliteal arteries increased from 3.2 +/- 0.2 mm to 3.6 +/- 0.5 mm or by 14.3 +/- 2.9% respectively (P < 0.01) after exposure to ultrasound energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood velocity patterns in poststenotic regions and velocity waveforms for myocardial inflow associated with coronary artery stenosis in dogs.

Velocity profiles across a vessel were investigated in poststenotic regions of the canine left coronary artery by our 80-channel 20 MHz ultrasound velocimeter. The velocity waveform in a small artery just before its penetration into myocardium was measured by our laser Doppler method. The poststenotic velocity configuration was characterized by a narrow region of high velocity with diastolic reverse flow near the wall which may dissipate energy. The velocity waveform in the distal small arteries exhibited increased systolic reverse flow with decreased diastolic forward flow, resulting in a remarkable reduction of coronary inflow into the myocardium.

Diagnosis of high posterior infarction: Experimental study through the use of body surface isopotential maps

This investigation was designed to diagnose high posterior infarction easily through the use of body surface isopotential maps. High posterior infarction was experimentally caused by ligation of the branch of the circumflex artery of the canine left coronary artery. Each dog had a series of maps recorded before and four weeks after experimentally induced myocardial infarction. The common features of maps in high posterior infarction are: 1) The positive area expanded into the dorsal surface so slowly that, in the middle stage of the ventricular depolarization, a large area of the dorsal surface was still covered by the negative area. 2) from the middle to the late stage, the absolute value of the minimum significantly decreased and absolute potential of the dorsal surface also significantly decreased. In conclusion, we propose that it is possibile to diagnose high posterior infarction through the use of maps.

Experimental studies of ST-T changes in electrocardiogram: effect of local or total hypoxemia of the canine heart on the unipolar lead electrogram and on the trans-membrane potential recorded from the ventricular epicardial surface

To clarify the mechanism of ST-T changes in electrocardiogram, these changes that appear on the direct unipolar electrogram recorded from the ventricular surface were compared with the changes of transmembrane potentials simultaneously recorded from the vicinity of direct unipolar electrogram. This study was conducted on the in situ canine heart under conditions of total and local hypoxemia. Method Seventy-seven mongrel dogs weighing about 15 kg were used, and each animal was anesthetized intravenously by pentobarbital sodium 25 mg per kg of body weight. Then the heart was exposed after performing thoracotomy under artificial positive pressure respiration. In order to prevent the undue movement of recording site on ventricular surface, the inner and outer rings attached to the supporting frame were placed over the pericardial surface, and then the portion of the pericardium within the inner ring was dissected away. Ringer's solution with the temperature of approximately 33°C was constantly dripped upon the epicardial surface, in order to prevent dryness. Using the central terminal system of Wilson, a unipolar surface electrogram was taken simultaneously with transmembrane potentials from the epicardium within the inner ring. The surface electrode consisted of tungsten wire 100 micron in diameter, and was gently placed on the ventricular surface by micromanipulator. The transmembrane potential of the individual cell was recorded from a flexibly mounted ultramicroelectrode such as described by WOODBURY and BRADY (1956). The indifferent electrode consisted of tungsten wire with a diameter of about 100 micron, placed 2 to 4 mm away from the site of penetration by microelectrode. Total hypoxemia of the ventricles was induced by letting a dog inhale the mixture-gas of oxygen 4% and of nitrogen gas 96% for from 6 to 8 minutes. For producing the local hypoxemia of the ventricle, approximately 120 ml of venous blood was taken from the femoral vein by syringe. At this time special care was paid to venous blood, that is, venous blood was kept from exposure to room-air by a layer of floating liquid paraffin in the syringe. This venous blood was kept at approximately 36°C. This venous blood was perfused at a pressure of 100 mmHg into the artificial coronary circuit made between the left carotid artery and the anterior descending branch of the canine left coronary artery (heparinized 500 units per kg/body weight). The room temperature was kept between 24 to 25°C through-out the experiment.