Myocardial beta-adrenoceptor density and plasma catecholamines in syndrome X

Abstract

Recent research has cast doubt on the ischemic hypothesis of etiology of syndrome X (anginal pain, ischemic-like changes in the stress electrocardiogram, but normal coronary arteriogram). Abnormalities of pain perception have been shown and abnormal sympathetic nervous system activation has also been implicated. The aim of this study was to test the hypothesis that downregulation of myocardial β adrenoceptors is demonstrable in patients with syndrome X. Such downregulation would be consistent with raised myocardial catecholamine concentrations. We performed positron emission tomography with 11C-CGP-12177 to measure β-adrenoceptor density. Plasma catecholamines were sampled simultaneously and assayed using high-performance liquid chromatography. Twenty syndrome X patients (11 female, age 57 ± 9 SD years, range 33 to 69) and 18 matched controls (9 women, age 50 ± 13 years, range 25 to 65; p = NS vs patients) were studied. Myocardial β-adrenoceptor density did not differ between syndrome X patients and controls: 8.0 (1.9) pmol/g for patients versus 8.3 (2.1) pmol/g for controls; p = 0.62. No differences were found between patients and controls for plasma norepinephrine (2.82 [1.07] and 2.76 [1.18] nM, respectively; p = 0.89) or for epinephrine (0.29 [0.14] and 0.30 [0.20] nM, respectively; p = 0.84). In patients with syndrome X, β-adrenoceptor density is normal and, by inference, myocardial catecholamines would also be normal. This weakens the case for a generalized enhancement of sympathetic activation in this disorder, although increased sympathetic reactivity during actual episodes of chest pain remains a possibility.