Effect of alpha(1)-adrenoceptor blockade on resting and hyperemic myocardial blood flow in normal humans

In the present study we aimed to assess the effect of alpha(1)-adrenoceptor blockade on resting and hyperemic myocardial blood flow in normal humans. Myocardial blood flow, at baseline and after dipyridamole, was measured with positron emission tomography and O-15-labeled water in 11 normal volunteers at control and during alpha(1)-blockade with doxazosin. Baseline myocardial blood flow during alpha(1)-blockade was not different from control, whereas coronary resistance was significantly lower (73.48 +/- 18.31 vs. 89.84 +/- 27.96 mmHg . min . ml(-1). g(-1); P < 0.05). After dipyridamole, myocardial blood flow during alpha(1)-blockade was significantly higher (3.50 +/- 0.75 vs. 2.58 +/- 0.54 ml . min(-1). g(-1); P < 0.01) and coronary resistance lower (25.30 +/- 7.37 vs. 33.89 +/- 7.04 mmHg . min . ml(-1). g(-1); P < 0.01) compared with control. In conclusion, in normal humans, dipylidamole-induced increase in myocardial blood flow is limited by alpha(1)-mediated coronary vasoconstriction.