The coronary collateral circulation in normal goats

Effects of antagonists for endothelin ETA and ETB receptors on coronary endothelial and myocardial function after ischemia-reperfusion in anesthetized goats

To compare the effects of antagonists for endothelin ET(A) and ET(B) receptors on the action of ischemia-reperfusion on endothelial and myocardial function, 30 min of partial or total occlusion followed by 60 min of reperfusion of the left circumflex coronary artery was induced in anesthetized goats treated with intracoronary administration of saline (vehicle), BQ-123 (endothelin ET(A) receptors antagonist) or BQ-788 (endothelin ET(B) receptors antagonist). During reperfusion after partial occlusion, coronary vascular conductance and left ventricle dP/dt were decreased after saline or BQ-788, and they normalized after BQ-123. In these three groups of animals, the coronary effects of acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) during reperfusion were as under control. During reperfusion after total occlusion, coronary vascular conductance and left ventricle dP/dt were decreased after saline, and they normalized after BQ-123 or BQ-788. In these three groups of animals, the coronary effects of acetylcholine but not those of sodium nitroprusside during reperfusion were decreased after saline, and they reversed after BQ-123 or BQ-788. Therefore, selective antagonists of endothelin ET(B) and ET(A) receptors may produce similar protection of coronary vasculature and myocardium against reperfusion after severe ischemia. Selective antagonists of endothelin ET(B) receptors, contrarily to those of endothelin ET(A) receptors, may be ineffective to protect coronary vasculature and myocardium against reperfusion after mild ischemia.

Coronary action of endothelin-1 and vasopressin during acute hypertension in anesthetized goats. Role of nitric oxide and prostanoids

Coronary reactivity to endothelin-1 and vasopressin during acute, moderate hypertension, and the role of nitric oxide (NO) and prostanoids in this reactivity was examined in anesthetized goats. Left circumflex coronary flow was electromagnetically measured, and hypertension was induced by constriction of the thoracic aorta in animals nontreated (7 goats) or treated with the inhibitor of NO synthesis Nw-nitro-L-arginine methyl esther (L-NAME, 6 goats) or the cyclooxygenase inhibitor meclofenamate (6 goats). Under normotension (19 animals), basal mean values for mean arterial pressure and coronary vascular conductance (CVC) were 89+/-3 mm Hg and 0.36+/-0.038 ml/min/mm Hg, respectively. Endothelin-1 (0.01-0.3 nmol) and vasopressin (0.03-1 microg) dose-dependently decreased CVC, which, for endothelin-1 ranged from 5+/-1% (0.01 nmol; P<0.01) to 66+/-4% (0.3 nmol; P<0.001) and for vasopressin ranged from 9+/-1% (0.03 microg P<0.01) to 41+/-3% (1 microg; P<0.001). During nontreated and treated hypertension, mean arterial pressure increased to approximately 130 mmHg (P<0.01), and CVC decreased (17%) only during L-NAME-treated hypertension. The effects of endothelin-1 and vasopressin on CVC were decreased by approximately 50% during nontreated hypertension, and this was abolished by L-NAME and was not affected by meclofenamate. Therefore, during acute, moderate hypertension, the coronary vasoconstriction to endothelin-1 and vasopressin is attenuated, which may be related with increased NO release but not with prostanoids.

Role of nitric oxide in vascular tone and in reactivity to isoproterenol and adenosine in the goat coronary circulation

The present study examined the role of nitric oxide in coronary vascular tone and in the coronary vasodilatation in response to beta-adrenoceptor stimulation and adenosine. In anesthetized goats, the effects of intracoronary and i.v. administration of the inhibitor of nitric oxide synthesis, N(w)-nitro-L-arginine methyl ester (L-NAME), and those of isoproterenol, adenosine and acetylcholine on coronary blood flow, measured electromagnetically in the left circumflex coronary artery, were recorded. Intracoronary infusion of L-NAME (30-40 microg kg(-1) min(-1), four goats) reduced resting coronary blood flow by 14+/-3% (P<0.05) without changing arterial pressure and heart rate. L-NAME (40 mg kg(-1), eight goats) i.v. reduced resting coronary blood flow by 19+/-4% (P<0.05), increased mean systemic arterial pressure by 22+/-3% (P<0.01) and decreased heart rate by 10+/-2% (P<0.05). These effects of L-NAME were partially, but significantly reversed by L-arginine (six goats). Isoproterenol (10-100 ng, eight goats), adenosine (0.3-10 microg, seven goats) and acetylcholine (3-100 ng, five goats), injected intracoronarily, increased coronary conductance in a dose-dependent way and, under control conditions, these increases for isoproterenol, ranged from 32+/-5% to 82+/-12%; for adenosine, 6+/-2% to 174+/-22%; and for acetylcholine, 39+/-5% to 145+/-15%. During i.v. L-NAME the increases in coronary conductance induced by isoproterenol and acetylcholine were significantly reduced by about 50 and 60% (P<0.05), respectively, whereas those induced by adenosine were significantly increased further (about 30-100%, P<0. 05). During L-NAME plus L-arginine, the effects of isoproterenol, acetylcholine and adenosine on coronary conductance were not significantly different from those under control conditions. Therefore, it is suggested that in the coronary circulation: (a) nitric oxide may produce a basal vasodilator tone under normal conditions; (b) nitric oxide may be an intermediate in the vasodilatation due to beta-adrenoceptor stimulation and acetylcholine, and (c) the vasodilatation due to adenosine is potentiated during reduction of nitric oxide production.

PCA50941, a new 1,4-dihydropyridine, reverses endothelin-induced cardiogenic shock in the anesthetized goat

This study was designed to test the hypothesis that the properties of novel 1,4-dihydropyridine PCA50941 could favor the recovery of cardiogenic shock. Coronary blood flow (CBF), measured with an electromagnetic flow probe placed on the left circumflex coronary artery, systemic arterial pressure and heart rate were recorded in 24 anesthetized goats; left ventricular pressure and dP/dt were also recorded in 19 of these goats. Under control conditions, intracoronary injections in 5 goats of PCA50941 (10-120 microg) caused smaller reductions of CBF than those of Bay K 8644 (0.3-10 microg) (the reduction of CBF by 120 microg PCA50941 was 25% and that by 10 microg Bay K 8644 was 43%), and i.v. infusions in 4 goats of PCA50941 (10-300 microg/min) did not modify CBF nor the other hemodynamic variables recorded, whereas i.v infusion of Bay K 8644 (10-30 microg/min) reduced CBF by 20% and increased arterial pressure, left ventricular pressure and dP/dt. During control conditions and endothelin-induced cardiogenic shock, respectively, the values for 15 goats were: for CBF, 33+/-4 vs. 16+/-4 ml/min; for mean arterial pressure, 88+/-4 vs. 60+/-5 mm Hg; for left ventricular systolic pressure, 102+/-5 vs. 75+/-4 mm Hg; for dP/dt, 1453+/-147 vs. 925+/-101 mm Hg/s (all P<0.05), and for heart rate, 77+/-6 vs. 81+/-6 beats/min (P>0.05). Intravenous infusion of PCA50941 (100 microg/min) reversed the hemodynamic variables from the shock state to control values within 20 min in 5 of 6 animals, whereas i.v. administration of Bay K 8644 (10-30 microg/min) was not effective in 4 of 5 animals, and the vehicle (DMSO) was not effective in none of 4 animals in reversing the hemodynamic shock state. Therefore, it is suggested that PCA50941, a novel 1,4-dihydropyridine, has a cardiovascular profile that might be suitable for treating cardiogenic shock states.

The effect of basic fibroblast growth factor on the blood flow and morphologic features of a latissimus dorsi cardiomyoplasty

Previous studies designed to determine whether latissimus cardiomyoplasty could be used to revascularize ischemic myocardium showed that after operation the latissimus was ischemic and had severely deteriorated. This study was undertaken to determine whether basic fibroblast growth factor, a potent angiogenic peptide, would improve the vascularity of the latissimus and enhance collateral formation between the muscle of the cardiomyoplasty and ischemic myocardium. In goats, myocardial ischemia was induced with an ameroid constrictor and cardiomyoplasty performed. The latissimus was continuously stimulated electrically at 2 Hz for 6 weeks and given four weekly bolus injections of human recombinant basic fibroblast growth factor (80 micrograms infused into the left subclavian artery). In eight animals, rates of regional blood flow were measured and both the heart and latissimus were evaluated histochemically. The latissimus blood flow rate was 0.114 +/- 0.029 ml/gm per minute, which was three times greater than that of historical controls (chronically stimulated latissimus cardiomyoplasty without basic fibroblast growth factor treatment; 0.042 +/- 0.007 ml/gm per minute, p < 0.05). Associated with the improved blood flow, there was significantly less evidence of skeletal muscle fiber dropout and muscle fibrosis in the animals treated with basic fibroblast growth factor. Latissimus-derived collateral flow to ischemic myocardium developed in five of the eight goats and averaged 0.288 +/- 0.075 ml/gm per minute. This flow was 42.8% +/- 15.7% (n = 5) of the flow required by normal myocardium (which was 0.728 +/- 0.095 ml/gm per minute). This value for latissimus-derived collateral blood flow was almost twice that of the historical controls (24.0% +/- 3.9%), but the increase did not achieve statistical significance (p = 0.08). These results hold the promise that basic fibroblast growth factor treatment might enhance the formation of extramyocardial collaterals to the heart and improve skeletal muscle function.

Acute electrical stimulation increases extramyocardial collateral blood flow after a cardiomyoplasty

We hypothesized that acute electrical stimulation of a latissimus dorsi cardiomyoplasty would augment the collateral blood flow delivered by the skeletal muscle to the heart. This hypothesis was tested in an animal model (13 goats) of coronary artery disease. Six weeks after a cardiomyoplasty was performed, myocardial collateral blood flow derived from the latissimus dorsi muscle was measured with colored microspheres when the muscle was at rest and during electrical stimulation of the thoracodorsal nerve at 1.25 Hz. The area at risk for ischemia averaged 13.37 +/- 2.08 g (mean +/- standard error), or 18.4% of left ventricular mass (n = 13). At rest, significant skeletal muscle-derived collaterals developed in 9 animals, and formed predominantly to chronic ischemic myocardium (mean +/- standard error, 0.07 +/- 0.02 mL.g-1 x min-1; n = 9), rather than infarct (0.03 +/- 0.02 mL.g-1 x min-1; n = 5), or normal myocardium (0.0005 +/- 0.0001 mL.g-1 x min-1; n = 9). Stimulation increased skeletal muscle-derived collateral blood flow to chronic ischemic areas to 0.38 +/- 0.09 mL.g-1 x min-1 (n = 9) (p < 0.05). During stimulation, the collateral flow was greater in the epicardium (0.46 +/- 0.11 mL.g-1 x min-1) than in endocardium (0.14 +/- 0.09 mL.g-1.min-1) (p < 0.05). This study demonstrates that electrical stimulation of a latissimus dorsi cardiomyoplasty increases extramyocardial collateral blood flow to chronic ischemic myocardium.

Collateral blood flow from skeletal muscle to normal myocardium

Collateral blood vessels from skeletal muscle to myocardium might supplement intramyocardial collaterals during periods of acute myocardial ischemia. This study was conducted to verify the existence of such collaterals and to measure their contribution to collateral flow. In 12 male goats, the innate coronary collateral system to a moderate size myocardial risk area was defined with colored microspheres, and a latissimus dorsi pedicle flap was then apposed to the heart. After 3 weeks, skeletal muscle to myocardial collaterals were characterized by (a) creation of vascular casts (three animals); (b) estimation of skeletal muscle to myocardial collateral blood flow (three animals); and, (c) measurement of total collateral blood flow to the risk area (innate plus skeletal muscle to myocardial collateral flow). Under a dissecting microscope the vascular casts revealed direct communications from the skeletal muscle which penetrated deeply into the myocardium. With the coronary artery to the risk area open, the estimated myocardial collateral blood flow derived from the muscle flap was 0.01, 0.02, and 0.04 ml/min. With the coronary artery to the risk area closed, there was no significant increase in total coronary collateral blood flow. Although the quantity of blood flow delivered by skeletal muscle collaterals was small, this study demonstrates that clearly identified collateral blood vessels form between skeletal muscle and myocardium in a cardiomyoplasty model. This raises the possibility that, under conditions more favorable to their development, extramyocardial collaterals from skeletal muscle might be exploited to augment the intramyocardial collateral system.

After a cardiomyoplasty, collaterals from skeletal muscle form to chronic ischemic myocardium

We measured the collateral formation between skeletal muscle and the heart after a latissimus dorsi cardiomyoplasty in an animal model that contained normal, chronic ischemic, and infarcted myocardium. The area at risk for ischemia was 27.0 +/- 3.2% of the left ventricular mass (n = 10, mean +/- SE). In five animals the risk area developed predominantly into chronic ischemic myocardium; in five others the risk area became an infarct. The collateral blood flow from the skeletal muscle to chronic ischemic myocardium (6.05 +/- 1.36 ml/100 g/min, n = 5) was higher than flow to the infarct (0.46 +/- 0.31 ml/100 g/min, n = 5). The collateral blood flow to normal myocardium was minimal (0.04 +/- 0.01 ml/100 g/min). The collateral blood flow appeared to be concentrated in the outer half of the left ventricular wall, with the epicardium having a higher skeletal muscle derived collateral blood flow than endocardium (p < 0.05). We conclude that after a cardiomyoplasty a collateral blood flow, which approaches clinical significance, is preferentially established between skeletal muscle and chronic ischemic myocardium. Enhancement of this collateral blood flow might provide a means to revascularize patients with presently inoperable coronary disease.