Increased levels of thromboxane A2 in peripheral and coronary circulation in patients with angina pectoris

Parathyroid hormone in coronary artery disease--results of a prospective study

Parathyroid hormone (PTH) influences the calcium metabolism of many different mammalian cell types; indeed, hypertension due to changes in muscle tone is a frequent symptom of hypercalcemic hyperparathyroidism. In a blind study of 81 patients with various forms of heart disease undergoing coronary angiography, the plasma concentrations of the midcarboxyl regional PTH immunoreactivity were determined. PTH concentrations were elevated in 26 of the 56 patients exhibiting organic coronary artery disease (CAD). The plasma PTH levels were highest in those patients with CAD affecting three vessels and in patients with evidence of myocardial infarction. PTH levels were not influenced by previous drug treatments, and did not correlate to stress hormone levels. We propose that increased PTH levels may be a marker for initiation or potentiation of calcium-dependent changes in vascular smooth muscle behavior inducing coronary functional and anatomic lesions typical of CAD.

Prostacyclin produced by the pericardium and its influence on coronary vascular tone

To determine the influence of pericardial fluid prostacyclin on coronary blood flow, the latter was measured in the circumflex artery of anesthetized dogs. Intraaortic infusions of angiotensin II (25 ng . kg-1 . min-1) reduced blood flow and released prostacyclin into pericardial fluid. Epicardial and pericardial superfusion with indomethacin (1 micrograms/ml) abolished prostacyclin release and significantly increased the coronary vasoconstrictor effect of angiotensin II; this treatment did not appear to affect vascular synthesis of prostacyclin. Pericardial prostacyclin may modulate the coronary vasoconstrictor effect of angiotensin, but its general role as a regulator of coronary vascular resistance is probably limited. A more important effect of pericardial prostacyclin may be exerted on the large coronary vessels in the epicardial surface. Release of prostacyclin into pericardial fluid represents a potential mechanism for opposing coronary vasospasm, especially if platelet activation is found to be a contributory factor in vasotonic angina pectoris.

Arterial and coronary sinus catecholamines in the course of spontaneous coronary artery spasm

We studied plasma catecholamine levels in 10 patients with frequent spontaneous episodes of coronary artery spasm to evaluate the role of the sympathetic nervous system. Peripheral venous norepinephrine in supine and upright postures, urinary excretion of catecholamines, and functional testing of the sympathetic nervous system did not differ from the same measurements in control subjects. Arterial and coronary sinus levels of norepinephrine and epinephrine drawn early in ischemia were not elevated over baseline; coronary sinus norepinephrine levels were higher than those in arterial samples and rose from 315 +/- 32 (pg/ml +/- SE) at the onset of ST elevation to 490 +/- 49 pg/ml late in ischemia (p less than 0.05). Plasma epinephrine levels, higher in arterial than coronary sinus samples, also rose significantly only late in ischemia, from 44 +/- 14 pg/ml to 148 +/- 35 pg/ml (p less than 0.05) in arterial blood and from 33 +/- 10 pg/ml to 108 +/- 29 pg/ml in coronary sinus samples (p less than 0.05). Generalized sympathetic nervous system activation is not likely to be the sole cause of coronary artery spasm.

Haemodynamic and metabolic effects of dazoxiben at rest and during atrial pacing

1 Thromboxane B2 (TXB2) levels were measured in three sites (coronary sinus, pulmonary artery, and femoral artery) at rest and during atrial pacing in 11 patients with stable angina pectoris. 2 There was a highly significant increase in arterial TXB2 on pacing (by up to 820 pg/ml) but there was no change in the thromboxane levels at the other two sites. 3 Dazoxiben 200 mg orally abolished the increase in arterial TXB2, but had no effect on systemic, pulmonary or coronary haemodynamics, no effect on myocardial metabolism and a variable effect on atrial pacing time to angina.

Platelet release and thromboxane synthesis in symptomatic coronary artery disease

The incidence and significance of platelet activation in myocardial ischemia was evaluated by serial measurement of plasma thromboxane B2 (TXB2) and beta thromboglobulin (beta TG) in plasma and urine in 98 patients admitted to a coronary care unit with chest pain. All measurements were normal in the 26 patients with noncardiac chest pain. Mean plasma TXB2 and beta TG concentration, but not urine beta TG, were elevated in the 25 patients with myocardial infarction and the 47 patients with angina. The beta TG levels remained normal in 61% of the patients with angina or infarction. The TXB2 levels were significantly higher in patients with recurrent episodes of angina at rest than in those without ischemic episodes after admission. There was a weak correlation between plasma TXB2 and plasma beta TG (r = 0.20, p less than 0.01) and between plasma and urine beta TG (r = 0.31, p less than 0.01). Results indicate that platelets are frequently activated with myocardial ischemia or infarction. However, the measurement of beta TG and TXB2 is of limited value in detecting or differentiating myocardial ischemia from infarction and therefore lacks clinical value in the management of patients with ischemic heart disease.

Platelet activation in clinical coronary artery disease and spasm

Current concepts of atherogenesis, based on animal models, suggest a role for platelets in the development of atherosclerotic lesions, possibly through the release of alpha granule constituents. Platelets may also contribute to the development of vascular spasm through thromboxane A2 production. Platelet activation in the coronary circulation in patients with coronary artery disease (CAD) should occur if these hypotheses apply clinically. We measured aortic and coronary sinus plasma levels of the platelet alpha granule constituent beta-thromboglobulin (B-TG) and thromboxane B2 (TX B2) by radioimmunoassay in 15 patients with severe atherosclerotic CAD, seven patients with angiographically normal coronaries, and five patients undergoing evaluation for coronary artery spasm (CAS). Compared with the controls, CAD patients had significantly greater transmyocardial release of B-TG (11.1 +/- 8.1 ng/ml, mean +/- SEM vs 62.5 17.2, p less than 0.05 by rank sum test); TX B2 gradients showed a similar trend but the difference was not statistically significant (-0.08 +/- 0.03 ng/ml vs 0.22 +/- 0.02, 0.05 less than p less than 0.10). Three of the five patients studied developed CAS which was associated with acute elevation in coronary sinus TX B2; the two non-CAS patients with drug provocation had undetectable coronary sinus TX B2. We conclude that abnormal platelet activation takes place in the coronary circulation of CAD patients, and that production of acute myocardial ischemia by CAS occurs with increased coronary sinus TX B2.

Thromboxane A2 in vasotonic angina pectoris: evidence from direct measurements and inhibitor trials

Thromboxane A2 (TxA2), an arachidonic acid metabolite causing vasoconstriction and platelet aggregation, is a putative mediator of coronary-artery vasospasm. To determine whether platelet-released TxA2 causes coronary arterial vasospasm, we measured plasma thromboxane B2 (TxB2, the inactive hydration product of TxA2) in the radial-artery and coronary-sinus blood of seven patients and performed therapeutic trials of antiplatelet agents in nine. Although coronary-sinus TxB2 levels rose from the base line approximately fivefold with spontaneous ischemia, samples drawn early in ischemia showed no rise over base-line values. Although a 150 mg dose of aspirin reduced urinary dinor-TxB2 levels by over 75 per cent, it had no effect on the course of the chronic recurrent form of angina pectoris due to vasospasm ("vasotonic angina"). Similarly, indomethacin had no effect on the frequency or duration of ischemia. TxA2 is unlikely to cause vasotonic angina, but it may be released during coronary vasospasm.