Effects of atrial pacing on arterial and coronary sinus endothelin-1 levels in syndrome X

Syndrome X may be caused by a coronary microvascular dysfunction, possibly due to abnormalities in coronary endothelial function. Previous studies sug gested that endothelin-l (ET-1) might be involved in the pathogenesis of sy ndrome X. Baseline arterial and coronary sinus ET-I levels were measured in 13 patients with syndrome X (10 women, 52 +/- 7 years) and in 8 control pa tients (5 women, 46 +/- 11 years). ET-I was also measured after atrial paci ng in 12 patients with syndrome X and all controls. To simultaneously asses s the activity of nitric oxide, guanosine 3'-5'-cyclic monophosphate (cGMP) was also measured in 11 patients with syndrome X and 7 controls. Baseline arterial (2.27 +/- 0.46 vs 1.90 +/- 0.22 pg/ml, p < 0.05) and coronary sinu s (2.03 +/- 0.43 vs 1.68 +/- 0.28 pg/ml, p = 0.06) ET-I plasma levels were higher in patients than in controls. After pacing, arterial ET-I levels did not change in either group and coronary sinus ET-1 levels were also unchan ged in controls. In contrast, coronary sinus ET-I increased significantly i n response to atrial pacing in patients with syndrome X (p = 0.023), and di fferences between coronary sinus ET-I levels of patients with syndrome X an d controls after pacing became highly significant (2.22 +/- 0.45 vs 1.69 +/ - 0.20 pg/ml, respectively, p = 0.006). No significant differences in arter ial and coronary sinus cGMP concentrations were found between the 2 groups, both at baseline and after pacing. Our findings suggest that an increased vasoconstrictor activity of microvascular endothelium is present in at leas t some patients with syndrome X and may be involved in the pathogenesis of the syndrome. (C) 1999 by Excerpta Medico, Inc.