Relaxation of coronary arteries by electro-mechanical decoupling or adrenergic stimulation

Characteristics of adrenoceptors and [3H]nitrendipine receptors of porcine vascular smooth muscle: differences between coronary artery and aorta

Characteristics of the bindings of [3H](-)dihydroalprenolol, [125I](-)iodocyanopindolol, [3H]prazosin, [3H]yohimbine, and [3H]nitrendipine to porcine coronary membranes were investigated and the results compared with studies of porcine aortic membranes. In the equilibrium binding study carried out in sarcolemma-enriched fractions, there were no major differences in the Kd values of these radioligands between coronary artery and aorta. However, the densities of beta-, alpha 1-, and alpha 2-adrenoceptors and [3H]nitrendipine receptors of coronary artery were 258, 12, 12, and 561 fmol/mg protein, respectively, while those of aorta were 37, 525, 1,000, and 215 fmol/mg protein. beta-Adrenergic agonists competed with [3H](-)dihydroalprenolol binding sites in coronary artery, the order of potency being (-)isoproterenol greater than (-)norepinephrine greater than (-)epinephrine greater than (+)isoproterenol. In case of aorta, the order was (-)isoproterenol greater than (-)epinephrine greater than (-)norepinephrine. The competition by (+/-)bisoprolol (beta 1-selective antagonist) and ICI 118,551 (beta 2-selective antagonist) for [125I](-)iodocyanopindolol binding sites in coronary artery resulted in nonlinear Hofstee plots (beta 1:beta 2 = 90%:10%). In case of aorta, linear Hofstee plots were obtained. From these results, we conclude that coronary beta-receptors in pigs are predominantly of beta 1-type, while those of aorta are of beta 2-type; regarding the relative population of adrenoceptors, coronary artery is beta-dominant (beta/alpha = 11), while aorta is alpha-dominant (beta/alpha = 0.02); compared with alpha-adrenoceptors, coronary artery has a greater number of [3H]nitrendipine binding sites (nitrendipine/alpha-adrenoceptor = 23) than aorta (nitrendipine/alpha-adrenoceptor = 0.14).

Antianginal and myocardial metabolic properties of verapamil in coronary artery disease

To determine the metabolic cost of administering an experimental calcium antagonist, verapamil, to patients with coronary artery disease, 12 such patients were studied at rest and during stress with atrial pacing before and after intravenous treatment with verapamil (bolus dose of 0.1 mg/kg body weight, followed by infusion at 0.005 mg/kg per min). The mean (+/- standard deviation) aortic pressure at rest (98 +/- 22 mg Hg), coronary sinus blood flow (88 +/- 17 ml/min) and myocardial oxygen consumption (10.7 +/- 2.4 ml O2/min) decreased to 88 +/- 20 mm Hg (p < 0.0004), 77 +/- 14 ml/min (p < 0.03) and 8.8 +/- 2.5 ml O2/min (p < 0.01), respectively, after administration of verapamil. With atrial pacing, these values were 105 +/- 25 mm Hg, 151 +/- 50 ml/min and 18.5 +/- 6.4 ml O2/min, respectively, before infusion of verapamil, and then decreased to 87 +/- 14 mm Hg (p < 0.006), 107 +/- 31 ml/min (p < 0.0002) and 13.3 +/- 4.4 ml O2/min (p < 0.001) during infusion. Angina occurred in all patients with atrial pacing before verapamil (threshold to pain: 93 +/- 67 seconds). After verapamil, the threshold to pain in six patients increased to 191 +/- 183 seconds; and no pain was experienced by the remaining six (p < 0.0005). Before administration of verapamil lactate extraction decreased from 24 +/- 9 to 10 +/- 11 percent (p < 0.0002) during atrial pacing, and 9 (75 percent) of the 12 patients exhibited electrocardiographic S-T segment depressions. After administration of verapamil lactate extraction normalized to 22 +/- 9 percent during atrial pacing, and the electrocardiogram reverted to baseline in all but one patient. These findings indicate that verapamil decreases left ventricular myocardial metabolic demands, and concomitantly greatly increases the threshold to angina.

The effects of diltiazem (CRD-401) on the membrane and mechanical properties of vascular smooth muscles of the rabbit

1 The effects of diltiazem on electrical and mechanical properties of vascular smooth muscles of the rabbit were examined by various experimental procedures. 2 In the pulmonary artery, diltiazem (0.1 to 10 microgram/ml) did not modify the membrane potential (-56 mV), length constant of the tissue (1.47 mm) or rectifying properties of the membrane. Diltiazem (0.1 to 10 microgram/ml) did not modify the membrane potential of the mesenteric artery (-62.5 mV). 3 Diltiazem (1 to 10 microgram/ml) suppressed mechanical responses of pulmonary and mesenteric arteries induced either by direct stimulation of the muscle (1.0 s pulse) or by neural activation (0.5 ms pulse, 30 Hz and 10 s total duration). Diltiazem suppressed the contraction induced by nerve stimulation to a greater extent than that induced by direct muscle stimulation. 4 When the depolarization-contraction relationship of the smooth muscle of the pulmonary artery was observed by voltage clamp technique, diltiazem (1 to 10 microgram/ml) raised the critical membrane potential to evoke contraction from 5 mV to 12 mV, and reduced the amplitude of contraction obtained at any given depolarization level. 5 In the pulmonary artery, diltiazem (10 microgram/ml) suppressed K-induced contraction and raised the mechanical threshold, while K-induced depolarization was not suppressed. Diltiazem (1 to 10 microgram/ml) also suppressed noradrenaline-induced contraction, raised the mechanical threshold and suppressed noradrenaline-induced depolarization. 6 The vasodilator actions of diltiazem on the vascular smooth muscle were compared to vasodilator actions observed with other Ca-antagonists.

Effects of ionophores A23187 and X537A on vascular smooth muscle activity

The ionophore A23187 initiated contractions in both dog coronary artery and rabbit aortic strips in a dose-dependent manner whereas X537A contracted rabbit aortic strips and relaxed KCl-induced contractions in dog coronary artery. Diphenylhydantoin (DPH) and verapamil ccompletely abolished KCl-induced responses in both vascular tissues. DPH (10(-4) M) partially prevented A23187-induced responses in both tissues and verapamil (33 micrometer) partially prevented A23187-induced responses in dog coronary artery but not in rabbit aorta. Phenoxybenzamine (10(-5) M), but not practolol, significantly reduced X537A-induced contractions in rabbit aortic strips but did not affect A23187-induced contractions in either tissue. The inability of DPH and verapamil to completely block the A23187 contractions leads one to conclude that these agents do not completely block calcium influx, or that A23187 does not work solely by increasing the permeability of the cell membrane to calcium. The effect of X537A on rabbit aorta, however, may be mediated at least partially, via release of catecholamines.

Coronary artery spasm as the cause of myocardial infarction during coronary arteriogarphy

Catheter-induced coronary artery spasm has been observed frequently. It is usually transient, reacts to the administration of nitroglycerin, and its distribution is generally confined to an area in proximity ot the intubated catheter. A 43-year-old woman with recurrent chest pain was found to have a rather long segment of tight proximal obstruction of the right coronary artery and experienced a myocardial infarction during coronary catheterization. Because of recurrent attacks of severe chest pain, coronary artery bypass surgery was performed which failed to result in significant improvement of her symptoms. Two repeat coronary cineangiograms seven weeks and three years after surgery revealed the proximal right coronary artery to be free of stenotic lesions or of luminal irregularities. After considering possible mechanisms of myocardial necrosis in the presence of normal coronary arteries it is concluded that myocardial necrosis can result from catheter-induced coronary artery spasm in spite of administration of nitroglycerin.

Reduction of the size of acute, experimental myocardial infarction by Verapamil

The effect of 0.1 mg/kg Verapamil on the extent of the ischemic area following ligation of a branch of the left descending coronary artery was studied in anesthetized open chest dogs. The sum of the ST-segment elevation during the entire period of occlusion in the epicardial ECG was 15 mV in control infarction compared to 9 mV (p smaller than 0.0005) when Verapamil was infused after ligation. Mean flow in the left descending coronary artery was reduced by coronary ligation alone on the average by 23%, but augmented by Verapamil for 5% above pre-occlusion control flow. Corresponding to the rise in the coronary flow and the drop in perfusion pressure under the influence of Verapamil, the increase of left coronary artery resistance induced by coronary occlusion was diminished. The positive effect of Verapamil on the size of myocardial infarction as estimated from the epicardial ST-segment changes is probably not induced by coronary vasodilatation, but by the Ca-antagonizing effect of this drug, as described by other authors.