AIM To study the influence of CPU 86017 and L thyroxin on vascular smooth muscle(VSM) contractions and the selective effect on α 1A and α 1B subtype. METHODS The contractions of rat thoracic aortic rings in two groups were studied to compare the inhibitory effect of CPU 86017 (30 μmol·L -1 ) on vascular smooth muscle from normal and levothyroxin treated rats and the selective effect on the Ca 2+ entry via receptor operated channel (α 1A ) and intracellular Ca 2+ release (α 1B ) stimulated by norepinephrine. RESULTS The percentage of VSM contraction induced by intracellular calcium release through activation of α 1B receptor in Ca 2+ free medium was 48.8±8.1 and 69.4±9.7 ( P <0.01) respectively in normal and L thyroxin treated groups. On the other hand, the percentage of VSM contraction induced by calcium entry through α 1A receptor was 47.7±5.0 and 22.1±9.4 ( P <0.01) respectively in two groups. While CPU 86017(30 μmol·L\+\{-1\}) was added, the contraction percentage induced by intracellular calcium release was 35.2±10.1 and 35.2±10.2 respectively, the contraction percentage induced by calcium entry was 13.9±7.1 and 20.7±7.5 respectively. CONCLUSION CPU 86017 has significant inhibitory effect on α 1A and α 1B subtype in the normal and L thyroxin treated rats. L thyroxin enhances effects on α 1B receptor and has relatively less effect on α 1A subtype.